Technical Proposal Low Level Windshear Alert System

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TELVENT
Almos
LLWAS
Low Level Windshear Alert System
Technical Proposal
Low Level Windshear Alert System
Title Low Level Windshear Alert System
Version 1
Date 30 November 2006
Ref
TELVENT Low Level Windshear Alert System
Almos
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Low Level Windshear Alert System
Table of Contents
Technical Proposal ................................................................................0
1. Introduction…………………………………………………………………4
1.1 Company Background & LLWAS Experience...................................................4
1.2 LLWAS System Summary................................................................................5
2. System Description..............................................................................6
2.1 System Performance.......................................................................................6
2.1.1 System Performance Overview ..............................................................6
2.1.1 LLWAS Top Level Description ................................................................7
2.1.1.1 System Overview...............................................................................7
2.1.1.2 System Diagram..............................................................................10
2.1.2 Master Station (MS) ............................................................................10
2.1.2.1 Controller Hardware .......................................................................10
2.1.2.2 Master Station Computer Configuration.........................................12
2.1.2.3 Multi-port RS232 ............................................................................12
2.1.2.4 Rack Configuration.........................................................................13
2.1.2.5 LLWAS Software.............................................................................15
2.1.2.6 Master Station LLWAS Displays .......................................................16
2.1.3 Remote Station (RS) ............................................................................18
2.1.3.1 System Description .........................................................................19
2.1.3.2 Wind Sensor Simulator ...................................................................20
2.1.3.3 Reliability Issues ..............................................................................21
2.1.3.4 Remote Station Electrical Power Requirements ...............................21
2.1.3.5 Environmental Conditions...............................................................21
2.1.3.6 Remote Station Obstruction Lights..................................................22
2.1.4 LLWAS Wind Sensors ..........................................................................22
2.1.5 Wind Masts………………………………………………………...……..23
2.1.6 RF and Land Line Data Links................................................................23
2.1.6.1 Detailed Communication Specification............................................23
2.1.7 Display Equipment ..............................................................................24
2.1.7.1 Overview ........................................................................................24
2.1.7.2 Alphanumeric Alarm Display (AAD).................................................25
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2.1.7.3 Graphical Alarm Display Screens (GAD)...........................................31
2.1.8 Interfaces...........................................................................................33
2.1.8.1 External Data Interface....................................................................33
2.1.9 Algorithm Implementation ..................................................................33
2.1.9.1 LLWAS Algorithm Functions............................................................35
2.1.10 Archiving/Playback..........................................................................36
2.1.11 Maintenance………...…………………………………………………38
2.1.11.1 Master Station Maintenance Screens ..............................................39
2.1.11.2 Built–In Test Equipment - BITE ........................................................42
2.1.11.3 Site Performance Evaluation System (SPES) .....................................44
2.1.11.4 Installation and Maintenance Tools.................................................49
2.1.12 System Modes (States) .......................................................................50
2.1.12.1 Real Time Normal ...........................................................................50
2.1.12.2 Real Time Degraded........................................................................50
2.1.12.3 System Support...............................................................................50
2.1.12.4 Initialization ....................................................................................51
2.1.12.5 Off..................................................................................................51
2.2 Configuration File ........................................................................................51
2.2.1 ACF……………………………………………………………………......53
2.2.2 DCF…………………………………………………………………...…...53
2.2.3 MCF, SCF……………………………………………………………….....53
3. Realibility, Maintability, Availability (RMA), and Supportability.............53
3.1 RMA Characteristics .....................................................................................53
3.1.1 Mean Time Between Failure (MTBF) / Mean Time Between Critical
Failures (MTBCF) .................................................................................53
3.1.2 Mean Time Between Corrective Maintenance Action (MTBCMA)........54
3.1.3 Built in Test and Fault Isolation capability ............................................54
3.1.4 Mean Time To Repair (MTTR) ..............................................................55
3.1.5 MTBF Evaluation .................................................................................56
3.1.5.1 Purpose ..........................................................................................56
3.1.5.2 References ......................................................................................56
3.1.5.3 Definitions ......................................................................................56
3.1.5.4 Approach........................................................................................56
3.1.5.5 Reliability Data................................................................................56
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3.1.5.6 Reliability Calculations ....................................................................57
3.1.5.7 Results ............................................................................................58
3.2 Supportability...............................................................................................58
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1. Introduction
1.1 Company Background & LLWAS Experience
Almos Systems is an ISO9001 quality endorsed company with extensive
experience in meteorological system design, development and production.
Almos products and services utilize extensive knowledge and experience in the
application of World Meteorological Organization (WMO) and ICAO codes and
rules.
Almos manufactures Automatic Weather Stations, communication equipment
and specialised computer equipment for control towers. Almos also specialises
in meteorological processing and display software. Almos offers system
design, integration, installation, and training and maintenance services of
meteorological systems.
The software package offered is based on the Almos “MetConsole”, which is
a commercial off-the-shelf product that was developed in partnership with the
Australian Bureau of Meteorology and Air services Australia (formally Civil
Aviation Authority) and has been in operational use in airports in Australia and
internationally for several years. A program to adopt the Almos MetConsole at
approximately 300 Australian sites has recently commenced after two years of
development and operational testing.
Almos Systems received a Federal Government grant to develop a graphics
based Phase III LLWAS software solution, as an extension of the field tested
Almos MetConsole package. This programme culminated in the installation of
the latest MetConsole version 2.3, including a complete LLWAS III NE master
station and display system at Darwin International Airport, which was the first
Phase III system outside USA. The system is owned and operated by the
Bureau of Meteorology but was manufactured, supplied and installed by
Almos Systems.
Systems using Almos MetConsole are in operational use at a number of
international airports around the world. Almos was among the first companies
to standardise on Windows NT technology. Operational MetConsole systems
are still running on the first version of NT and on the latest versions of NT.
The Remote Stations offered are based on the Almos Automatic Weather
Stations, which have been exclusively adopted by the Australian Bureau of
Meteorology. A modernisation program to replace all weather stations at
Australian civil and military airports is almost complete. Hundreds of Almos
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weather stations have been providing aviation and synoptic information for
several years. These systems operate in harsh and remote locations; yet have a
field proven MTBF of more than 35 years.
In 1996, Almos Systems was selected to supply Remote Stations for the FAA
Phase III LLWAS (NE) program. These units were designed and developed to
the point where the FAA project staff witnessed the type and factory testing
and 40 units were delivered.
Ongoing support and maintenance is available from our factories in Australia
and The Netherlands and from technology centres across the world in North
and South America, Spain and China.
Almos is a developer and manufacturer of LLWAS equipment, and has been
manufacturing LLWAS equipment since 1996 as a logical extension of our
commitment to the aviation weather industry. Our experience in both
developing products for aviation weather systems, and managing installations
of these systems ensures that we can provide the most qualified installation
support and services to all of our customers.
1.2 LLWAS System Summary
The Almos LLWAS-III system is a component of Almos’ advanced MetConsole
Aviation/Meteorology display and processing system. The modularity of
Almos’ design ensures that the provided LLWAS will meet and exceed lifetime
requirements while providing a maximum of future expandability options if
required.
The main MetConsole system is a completely configurable software package
designed to operate under Windows environments (95, 98, NT, 2000,
2003,…). A wide variety of communications, display and processing modules
may be included with a MetConsole system to provide the required
functionality.
In addition, dual server operation of the MetConsole package ensures that
system configuration and servicing may take place without interruption of the
LLWAS detection algorithm.
Additional modules may be ordered initially or added later, including ATIS
(computer generated voice, data output, or operator-recorded message),
METAR/SPECI, AFTN integration and a variety of standard WMO messages,
data input/output and observer screens. MetConsole is designed to allow you
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to completely integrate your Aviation computer systems, either now or in the
future.
The MetConsole LLWAS component uses a communications and processing
design that has been installed and tested in a number of different
environments, including Darwin International Airport (Australia), Sungshan
and Chiang Kai Shek Airports (Taiwan), Bilbao and Tenerife Airports (Spain)
and Kuwait International Airport (Kuwait).
Key points in the selection of an Almos MetConsole solution include:
• Cost effective
• User friendly
• Extensive, well written user help & manuals
• High speed Processing
• Extremely Reliable Communications
• Robust Equipment
• Commitment to Quality and Reliability
• Committed to Customer Satisfaction
• COTS processor - No customisation required.
• Experience in design and manufacture of LLWAS equipment
• Worldwide coverage
• UCAR Licensee since 1996
• Easy maintenance makes better use of manpower.
• Expandable software configurable to each customer’s unique
requirements.
• Easy connection to DWR LLWAS Radar.
2. System Description
2.1 System Performance
2.1.1 System Performance Overview
Almos’ LLWAS is implemented using Almos’ MetConsole software system to
provide both a proven, reliable design as well as a system that is easy to use
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and maintain. (MetConsole is the same system software used for AWOS, ATIS,
ASOS and other system products.)
This document describes the proposed implementation of this system to
ensure that the LLWAS detection system meets or exceeds all internationally
recognised requirements.
Almos’ LLWAS system uses the UCAR Phase-III LLWAS algorithm. Coupled
with a fault tolerant communications system that well exceeds the standard
1.05e7 bit error rates, Almos’ probability of detection meets that promised by
the UCAR Phase-III LLWAS algorithm for any given airport configuration.
The Almos LLWAS system provides the detection performance for a standard
airport configuration as included in the following table:
POD 94% The probability that some alert (WSA or MBA) is issued
whenever microburst intensity exceeds 15 knots
POD:MB 97% The probability that some alert (WSA or MBA) is issued
whenever microburst intensity exceeds 30 knots.
PID:MB 92% The probability that an MBA is issued whenever
microburst intensity exceeds 30 knots
PFA:MB 3% The probability that an issued MBA is false; it is not
related to any part of a microburst life cycle.
POW 7% The probability that an issued WSA is an over warning;
the event is a microburst with strength less than 30
knots.
PUW 8% The probability that an issued WSA is an underwarning;
the event is a microburst with strength
greater than 30 knots.
Determining an exact POD at each airport is possible only through operational
use with the installed configuration, as localised meteorological, topographic
and geographic features will affect the resulting performance.
2.1.1 LLWAS Top Level Description
2.1.1.1 System Overview
Remote Station Network:
The system to be installed at the airport consists of a network of eight WAWS
(Wind-only Automatic Weather Station) units. The number of WAWS
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required at a site is dependent on the results of a site survey, which takes into
account the configuration of the runways, the topography of the desired area
of coverage.
Depending on the form of communication used, this network may consist of a
combination of radio (Model 2100-Z-RAD) or landline (Model 2100-Z-LDL)
WAWS units.
To provide master station communications to the landline and radio networks,
two Master Station Communication Set units are to be installed. A landline
MSCS (2100-Z-MSLL) provides a communications hub for the landline WAWS
units, and a radio MSCS (2100-Z-MSRD) provides a communications hub for
all radio WAWS units.
Because the LLWAS Algorithm is configured only to operate on fixed station
addresses, spare WAWS units can be tested by setting them outside of the
range of the ‘operationally in use’ WAWS network. The stations being tested
can then be queried and run as normal but without any data being used by
the LLWAS calculation or displayed on windshear display workstations.
Master Station:
The master station consists of a dual redundant server configuration (primary
server with hot backup). Serial and Parallel Multiplexers provide
communications channels to whichever server is designated the ‘hot’ server
through a failover process. This redundant system ensures that the system
remains operational even in the case of a server failure.
RS232 threshold wind interfaces and MSCS communications are connected to
the Serial multiplexer.
A keyboard/video/mouse extender allows the monitor keyboard and mouse
that form the system console to access both servers and to be located outside
of the rack if desirable.
The Server computers operate Almos LLWAS MetConsole, and provide a
TCP/IP socket for external interface. A multi-port RS232 controller greatly
extends the I/O communications capabilities of each server PC without
providing any significant extra workload on the PC.
LAN
All computers are connected to a central UTP hub. This hub configuration
ensures that any loss of communication or cable damage on any single system
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does not affect any other system. The hub is mounted close to the server pair
for easy maintenance and inspection of the server connection. A description
of the server and hub hardware is provided in the section describing Rack
Configuration.
A third PC, either installed in the equipment room or a more remote location,
processes data archiving and provides an archive replay facility.
Operator Workstations
Meteorological Workstations shall be located in the Meteorological office and
Meteorological observation room.
LLWAS alert displays shall be installed in the Air Traffic Control Tower.
The number of these workstations may be increased without practical limit.
Using a standard PC running a MetConsole client, these systems provide
display and processing functionality. Because of the network hub
configuration, disconnection (or software/hardware/cable fault) on any PC is
isolated from the remainder of the network and ensures that the tower
process carries on using the remaining systems.
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2.1.1.2 System Diagram
2.1.2 Master Station (MS)
The Almos Master Station consists of two main components: A Master Station
Communications Set (MSCS) providing communications to all remote stations,
and a dual-redundant MetConsole Server Pair providing data processing and
storage.
2.1.2.1 Controller Hardware
2.1.2.1.1 Master Station Communications Set
Two models of MSCS unit are used. 2100-Z-MSRD provides radio
communications with up to 16 Radio WAWS units (2100-Z-RAD) on a single
channel. A single RS-232 communications port provides data
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communications to a MetConsole server PC.
Lightning and surge protection are built in.
Mean Time between Failure (MTBF) for the
MSCS electronics is 40,000 hours. 2100-Z-MSLL
is a landline version providing landline
communications with up to 20 Landline WAWS
units (2100-Z-LDL) on a single telephone cable.
Interface to the PC is the same as MSRD, using a single RS-232
communications port. Lightning and surge protection (transformer isolation)
are built in.
2.1.2.1.2 Data Multiplexer / Switch
Almos RS-232 Multiplexer provides automated server data changeover in the
event of a server failover. This device and the MetConsole interface software
ensure that server failover is performed in the minimum amount of time and
without requiring operator intervention.
Multiplexer Overview
MASTER STATION
COMMUNICATION
SET
(LANDLINE)
MASTER STATION
COMMUNICATION
SET
(RADIO)
WIND
REMOTE
STATION LDL
WIND
REMOTE
STATION LDL
LANDLINE REMOTE STATION
O
WIND
REMOTE
STATION RAD
WIND
REMOTE
STATION RAD
RADIO REMOTE STATION
NETWORK
...
TO MASTER STATION PC
TO MASTER STATION PC
ADDITIONAL
STATIONS
ALMOS
MULTIPLEXER
MCS-RADIO
MCS-LANDLINE
EXTERNAL INTERFACE
EXTERNAL INTERFACE
EXTERNAL INTERFACE
REMOTE SITE SUPPORT
EXTERNAL INTERFACE
PRIMARY
SERVER
SECONDARY
SERVER
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2.1.2.2 Master Station Computer Configuration
The Master Station computers, like all computers used in the Almos LLWAS
MetConsole network, are Intel Pentium architecture PCs operating Windows
Server version of Operating System.
A DVD-ROM is provided standard on all PCs, allowing simple software
installation from an Almos LLWAS MetConsole install DVD. The Almos DVD
installation process is an extremely simple process designed to require a
minimum of operator supervision, making better use of valuable maintenance
engineers’ time.
Soundcards are installed on all PCs for the purpose of providing audible
alarms. LCD displays are offered for all display PCs and include integrated
brightness controls for use in a tower environment. Displays include
integrated speakers for simplified alert volume control and muting.
A high capacity Hard Disk is installed on both server PCs for the purpose of
storing data online.
The choice of the Windows Server operating system follows Almos’
commitment to quality by integrating with high quality, proven operating
systems in the critical aviation environment.
2.1.2.3 Multi-port RS232
Standard Personal Computer architecture limits the PC system to 4 RS-232
ports. Standard Airport systems often require many more ports in order to
cope with the large variety of incoming and outgoing data.
The Moxa Multi-port RS232 controller
attaches to the expansion bus of a
Master Station PC (two are supplied;
one for each Master Station) and
extends the number of ports available
on the PC significantly. These
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controllers are commonly used in high-end airport and meteorological
processing systems.
Each module installed supplies 16 additional high-speed ports; an onboard
RISC processor reduces PC workload allowing more efficient CPU utilization.
The Moxa controllers to be installed will interface to Master Station
Controllers, a modem provided for remote support and other RS232 data
input/outputs.
2.1.2.4 Rack Configuration
Proposed Rack Configuration for the ATC equipment room is as shown
below.
Incoming network cables (through the floor) are
connected to the UTP network hub via a patch
panel. The patch panel allows easy access to
network cabling. The hub is connected to both
server PCs, arranged side by side and clearly
marked “Primary” and “Secondary”.
Both Multi-port Moxa controllers are mounted
above the PCs, and ports from the Moxa
controllers and PC Printer ports are connected
directly to adjacent Serial Multiplexer / Parallel
Multiplexer units. These cables are then run
down through the floor to their various devices.
An intelligent Keyboard, Video & Mouse (KVM)
switch allows the user to switch the system
console screen to display either server’s data.
While the keyboard and mouse are being used
on one server, the KVM switch maintains
communications with the other unit, preventing
loss of signal common to simple switching
devices.
A modem provides dial-up support access and is
software secured (modem hangs up on receipt of
a call and automatically dials a dedicated support number, allowing only
access through the support office).
PRINTER
PAPER TRAY
POWER SUPPLY
MODEM
PC SWITCH
M/S
SRV-A
KVM EXTENDER
LAN HUB
PATCH PANEL
M/S
SRV-A
MOXA-A-1
MOXA-A-2
MOXA-B-1
MOXA-B-2
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A 19” CRT monitor, keyboard and mouse are provided external to the rack for
use as a System Console.
Controller Software
The Master Station Communications Set (MSCS) communicates with remote
stations using a selective-retry, multi-drop binary communication protocol.
The efficient design of this system was demonstrated during testing and trials
with the FAA during the commissioning phase of the Almos LLWAS MSCS
design in 1997. For a very detailed discussion on the communication protocol,
please see below the section under RF and Land Line Data Links entitled
Detailed Communication Specification.
The system is designed to provide reliable communications in line with FAA
LLWAS specifications. This reliability has been proven to representatives of
the FAA Phase III LLWAS program.
All communications between the Remote Stations and the Master Station is
performed at 2400 baud. Due to the extremely high efficiency of the protocol
it is not necessary to use a higher baud rate in order to satisfy the data
transfer rate requirements of the system.
Low baud rates like 2400 are considerably more noise immune than high
baud rates like 19,200 baud and therefore are a much better option in noisy
environments, such as radio communications surrounding an airport.
Bit error rate: <10-5
Communications Reliability: > 99.9% (48Hr MER < 10-4, 1Hr MER < 10-3)
The remote station communication
system uses a highly advanced binary
communication protocol. This was
developed specifically for the FAA Phase
III LLWAS programme and has been
proven to exceed the strict
communication efficiency requirements
that were defined for that specification.
The MSCS polls all the remote stations
at the beginning of the system cycle,
which is typically 10 seconds, and then
waits sufficient time for all the units to
respond.
REPOLL
SAMPLE 4 STATION POLL CYCLE
RS3 REPLY
MISSING REPLY
RS2 REPLY
RS1 REPLY
POLL
REPOLL
RS4 REPLY
MISSING REPLY
TIME
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All units for which a response was not received are then selectively repolled
until the end of the data acquisition time. This period is calculated to
leave sufficient time for the data processing, display and archiving functions
of the system.
RC and Linear averaging is performed on board the Remote Station WAWS
unit. This reduces the transmitted packet size and greatly enhances the
reliability of the communications system. This approach was witnessed and
approved by FAA personnel during type testing.
For Centrefield wind gust, the WAWS unit reports ten-second gust
information. This data is then processed by the MetConsole Server and
displayed on Operator Workstations.
2.1.2.5 LLWAS Software
Almos systems’ implementation of the UCAR Phase III Algorithm uses an
efficient implementation based on and tested against the Version 1990.02
Algorithm Specification. The system is designed to allow easy expansion to
accommodate FAA approved enhancements to this algorithm.
2.1.2.5.1 LLWAS Configuration
All MetConsole stations are configured through a single shared configuration
database. This database file contains configuration information pertaining to
the role of each station on the network (primary server, secondary server,
archiving PC, SPES workstation, operator workstations, displays etc). In
addition, the configuration database contains LLWAS parameters contained in
the ACF, SPES thresholds & parameters, DCF configurations and other
configuration data.
Figure 1 - LLWAS System Configuration (Typical)
SYSTEM CONFIGURATION (SCF) and
MAINTENANCE CONFIGURATION
(MCF) (Averaging constants,
Displays, Parameters, etc)
AIRPORT CONFIGURATION FILE
(ACF)
DISPLAY CONFIGURATION FILE
CONFIGURATIO
DATABAS
(METCFG.MDB
AAD DISPLAY
SYSTEM
INPUT DEVICE
ARCHIVE STATION
KEYBOAR
D &
MOUSE
AAD DISPLAY
SYSTEM
INPUT DEVICE
AAD DISPLAY
SYSTEM
INPUT DEVICE
RAW CONFIGURATION FIL ES
& PARAMETER S
SHARED
(BOTH
LLWAS MetConsole
Overvie
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The advantage of this shared configuration database approach is that systemwide
configuration can be achieved through reconfiguration of a single
central source file. The configuration database is centrally stored and changes
to this file are automatically integrated by MetConsole instances operating
across the network.
2.1.2.6 Master Station LLWAS Displays
All MetConsole screens are constructed using a configuration database. This
configuration database defines the names of each
‘screen’, the ‘screen objects’ to be displayed on
each screen, and the data item(s) to be displayed
by each ‘screen object’.
This design is extremely flexible and allows a
maintenance engineer to easily change the LLWAS
screens to reflect new additional sensors and other
equipment.
A number of screen objects are non-LLWAS specific, and will be used on
Maintenance and server displays to display the current status of various
variables such as sensor status, detected wind speed & direction etc. (LLWAS
display objects are described under the section titled Display Equipment.
2.1.2.6.1 System Overview Window
A ‘System Overview’ window provides a tree control containing all configured
remote stations, configuration parameters and statistics, and communications
information (also available in comprehensive form through a separate ‘Ports’
window).
Figure 2 - The system overview window provides comprehensive data views.
CONFIGURATION
DATABASE
(METCFG.MDB)
RAW CONFIGURATION FILES
& PARAMETERS
SHARED DATABASE
(BOTH SERVERS)
LLWAS MetConsole Display Configuration Overview
SCREENS
SCREEN OBJECTS
OBJECT TYPES
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The ‘System Overview’ window will only be accessible by the Maintenance
user and is not required for ATC users.
This window provides information about each LLWAS data variable, overall
communications status, and specific Remote Station diagnostic information.
Variable information may also be queried from all user screens, if the user has
sufficient security access.
Figure 3 - Query data from a user screen.
Variable information includes comprehensive data query options, with all
variables displayed in logical category divisions.
Figure 4 - Remote Station data views – LLWAS remote station statistics
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A System Overview tree display is also provided in the System Overview
window, and displays the current connection status of all remote
components of the LLWAS system in a graphical and easy to read manner.
Figure 5 - System overview (Sungshan airport example)
Having well organized graphical tools to aid in diagnosing faults and
troubleshooting ensures simple system maintenance.
2.1.3 Remote Station (RS)
The Almos Systems Remote Stations (RS) are also called Wind Automatic
Weather Station (WAWS). The function of these devices is to collect and
transmit wind speed and direction information back to a central monitoring
site.
The acquired data is transmitted to a Master Station Communications Set
(MSCS) at the central monitoring facility via a radio network (radio option) or
optional landline network (landline option).
Up to 16 radio or 20 landline WAWS can be connected to one MSCS. With
multiple MSCS, one Low Level Wind Alert System (LLWAS) may have up to
256 WAWS units.
The WAWS may be powered from 120VAC / 60Hz, 220VAC / 60Hz or
240VAC / 50Hz or from a Solar Power Set.
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2.1.3.1 System Description
The WAWS includes the following electrical subassemblies:
• ALMOS 2100-Z CPU Board
• Power Supply System
• Radio Interface and Radio Heater (Radio Option)
• Radio & RF Surge Suppressor (Radio Option)
• Line Isolation Board (Optional Landline Option)
• Solar Power Set (Solar Power Option)
• Stainless enclosure
• Designed for extreme environmental conditions:
• Altitude: 10,000 feet operating, 50,000 feet non-operating.
• Operating temperature: -40C to +70C
• Blowing Rain: Present
• EM interference: FCC class A compliant
• Humidity: <15% to 100% operating.
• MTBF: 272,945 hours (31.2 years)
For the location of the items inside the WAWS, refer to drawing
AS842-01-2 in appendix II of the WAWS Installation and Maintenance
Manual.
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Figure 6 - WAWS Block Diagram
2.1.3.2 Wind Sensor Simulator
Each remote station will include a wind sensor simulator, providing selectable
values for wind speed and direction. The simulator can be remotely operated
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over the radio or cable link or locally operated using the built-in maintenance
port.
2.1.3.3 Reliability Issues
Mean Time Between Failure (MTBF) for the remote station electronics is
40,000 hours.
Preventative maintenance requirements for the remote station (not including
sensor) do not require more than one visit per year to each remote site.
No LRU failure can cause damage or interfere with the operation of any other
LRU. In addition, high voltage suppression is provided using gas discharge
tubes and transorb devices. This is considered superior to the optical isolation
used by many manufacturers. As a result, no Almos weather station has ever
caused damage to other network elements, even during a direct lightning
strike.
Protective devices are provided on all power, sensor and communications
connections in the remote stations. All connections (except RF) utilise gas
discharge tubes and transorb devices, providing two-stage protection.
A coaxial surge protector is provided on the incoming RF connection.
2.1.3.4 Remote Station Electrical Power Requirements
Power may be supplied using a solar panel with a maintenance-free sealed
lead-acid battery set and a built in solar regulator, or commercial mains
power.
Average power requirements for LRUs (including wind sensor and radio) are
approximately 160mA at 12 V.
All remote stations are battery backed with a maintenance free sealed leadacid
battery, providing at least 32 hours of operation.
2.1.3.5 Environmental Conditions
The remote stations offered fully satisfy the military temperature range
requirements. Extremely high temperatures of over 55°C may be endured
without adversely affecting the operating of the system. The design of the
equipment shelter also helps to keep the temperature of the electronics as
low as possible in high ambient temperature conditions.
The enclosure’s protective category corresponds to NEMA-4X.
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• Altitude: 10,000 feet operating, 50,000 feet non-operating.
• Operating temperature: -40C to +70C
• Blowing Rain: Present
• EM interference: FCC class A compliant
• Humidity: <15% to 100% operating.
• MTBF: 272,945 hours (31.2 years)
2.1.3.6 Remote Station Obstruction Lights
Obstruction lights are fitted to all masts supplied. The type of obstruction
light offered is the Obelux 32-12-HTS. This FAA and ICAO compliant
obstruction light offers the following benefits:
• Long maintenance intervals
• Low energy cost (less than 10W)
• Supply power voltage variations do
not affect light output.
• Very low total lifetime costs.
• Low wind load
• ICAO & FAA compliance
• Exceeds temperature requirements –
–55C to +80C operating
2.1.4 LLWAS Wind Sensors
There are several options available for the wind sensor, both cup-and-vane
and ultrasonic types.
Sensors are supplied by selected third party suppliers. Almos do not
manufacture sensors and therefore sensor selection is solely based on
independent, unbiased evaluation of technical performance and sale price.
Several types of wind sensors are supported by the Almos WAWS aleady
however any type can be interfaced should the customer’s preference fall
outside of the sensors for which drivers already exist namely:
Vaisala WAA/WAV151 - Cup and Vane
Vaisala WS425 - Ultrasonic
METEK USA1 - Ultrasonic
Met-One - Ultrasonic
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All ultrasonic sensors are virtually maintenance free. Only annual checks are
required to ensure that the sensing elements are free of debris.
Each sensor is directly connected to the Almos WAWS (Remote Station) unit
using either a serial (RS232 or RS422) link or a digital interface. This allows the
Almos WAWS to perform all data averaging, logging, error correction and
communications functions directly on the measured data.
This architecture allows provision of any range of measurement averages,
from instantaneous to very long average periods. In an LLWAS environment,
the standard measurement period is the 10 second RC average (the System
Cycle).
2.1.5 Wind Masts
Most LLWAS systems are implemented with 10m, 15m or 20m poles. In most
case 10m is sufficient. Higher poles are sometimes installed to avoid
obstructions. While it is best that all poles are the same height, this is rarely
achieved in practice.
Poles need to be strong enough to withstand high winds and also to provide
easy access to equipment for maintenance.
Almos offers both frangible and non-frangible tilting masts.
2.1.6 RF and Land Line Data Links
2.1.6.1 Detailed Communication Specification
The remote station is supplied with facilities for both radio (RF) and landline
(non RF) communications.
2.1.6.1.1 RF communications
RF communications utilises a multi-drop radio protocol that allows up to 16
remote stations to communicate on the same radio channel.
RF communications uses digitally tuned Data Radios. The radio frequency and
other parameters are fully programmable. Assuming that there are no
obstructions and line-of-sight problems, reliable communications is assured
between the master station and any remote station up to a distance of 7
nautical miles. Under ideal conditions, transmission paths of up to 25 nautical
miles are possible.
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9 element 9dB directional yagi antennas are used at the remote stations and
3dB omni-directional antennas are used at the master stations. The yagi
antenna is stainless steel. The omni-directional antenna has a stainless steel
mounting tube with a fibreglass radome.
2.1.6.1.2 Landline communications
Landline communications utilises a multi-drop modem configuration that
allows a number of remote stations to be connected together on a single
landline channel. The recommended maximum number of units on a landline
link is 20.
To prevent faulty remote stations from saturating the communication channel
the remote stations are fitted with a watchdog circuit that disables
transmission in case a remote station is not operating correctly.
The master station configuration may include several Master Station
Communication Sets (MSCS), enabling communications via any combination
of RF and landline links. Multiple RS232 communications ports are required on
the master station PC for communications to the remote stations.
2.1.7 Display Equipment
2.1.7.1 Overview
The Low Level Windshear Alert System (LLWAS) provides two methods of
displaying windshear and microburst alarm data on user workstations.
These are:
• AAD (Alphanumeric Alarm Display) – Text Only
• GAD (Graphical Alarm Display) – Text and Graphics
All display devices use a high resolution, high brightness LCD colour monitor
and may display either display format (graphics or text).
The AAD provides the user with data in a textual display. This screen shows
the current windshear status of the airport in textual form. It gives the status
of a selected number of runway thresholds and a centerfield location.
In order to use the AAD most effectively, the user can select a “runway
threshold configuration” that matches their current frame of reference. The
user can choose to view windshear information for a selected group of
available runway thresholds. This allows Air Traffic Controllers to concentrate
on areas that are within their specific sphere of control.
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The GAD is used to show a map of the airport and the location of wind
sensors. If a windshear or microburst is detected, then the map will show,
using coloured highlights, those areas of the airport affected.
2.1.7.2 Alphanumeric Alarm Display (AAD)
AAD display screens are an integrated screen object displaying a number of
runway threshold winds & windshear reports, status variables and centrefield
information.
While the AAD simply reports the status of single data elements, these
elements can be configured to use backup sensors for centrefield and
threshold winds, providing ATC with constant data.
All parameters on the Almos AAD are completely configurable, including
number of lines per display (8 message + 2 status), colours & highlighting
rules, audible alarms and line formats.
Audible alarms are sounded through the PC sound card when a hazardous
wind shear is detected. The duration, in seconds of this audible alarm is
configurable and default duration is 30 seconds.
2.1.7.2.1 General Description
The AAD is a multi-line read-only display having the following features:
• Threshold wind data can be selected and displayed for each runway
• Displays LLWAS messages in a syntax that is configurable. (This
• allows easy changes to be made to the system's output without changing
the software).
• Displays a database-configurable number of rows and columns per
• display.
• Status information is displayed on the AAD.
• Centrefield & alarm information is displayed on the AAD.
• Audible alarm, which sounds at full volume. (Users can adjust the
• volume using a volume control).
• A configurable flashing/hi-lighting method can be selected for new
messages.
• Can be configured to indicate alarm updates for particular thresholds for a
specified period of time.
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• The system time is displayed on the AAD.
• Auto-scales character size to the selected AAD object size. (The font is
configurable).
• Displays a configurable Communication Failure message if the server is
not found after a timeout period.
• Displays missing wind data as a configurable value.
• Does not display any persisted data. (No LLWAS messages or wind
information is persisted).
• All configurable parameters have a default setting.
While the AAD reports the status of single data elements, these elements can
be configured to use backup sensors for centrefield and threshold winds,
providing ATC with constant data.
2.1.7.2.2 The Screen
All parameters on the AAD are configurable, including the ten available
display lines (8 message + 2 status), colours & highlighting rules, audible alarm
and line formats.
Each message line provides 6 possible items of information:
1. Runway identifier
2. Alert type
3. Wind speed gain or loss
4. Location of windshear or microburst
5. Threshold wind direction and speed
6. Possible alarm outside the network zone
When the system is operating normally, line 9 (second-last line from the
bottom) is blank. If a problem occurs, the text DEGRADED, SUPPORT,
INITIALIZATION or OFF is displayed, to indicate the state of the system.
Line 10 is reserved for LLWAS system messages. When there is active
communication between the server (master station) and AAD, the following
information is displayed:
• Centrefield wind direction and speed
• Centrefield gust speed
• System time (in UTC)
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• Audible alarm state (On or Off)
If no information is received from the server within a configurable time period,
the AAD will blank and display “COMMUNICATION FAILURE” on line 10.
The following identifiers are used in the AAD:
A Approach
D Departure
LA Left approach
LD Left departure
RA Right approach
RD Right departure
CA Centre arrival
CD Centre departure
ALM Alarm
MBA Microburst alarm
WSA Windshear alarm
G Gust
K Knots (wind speed)
+/- Gain or loss (change in windspeed)
CF Centrefield
MF Nautical “Miles Final” (final approach)
MD Nautical “Miles Departure”
(departure corridor)
RWY Location (runway)
* Possible alarm outside the network zone
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Figure 2-7 is a typical example of an AAD.
Figure 2-7 Typical AAD
Referring to the example display above, line 1 provides the following
information:
10A Operational runway “10 Arrival”
WSA Windshear alarm
46K+ Estimated wind speed gain “46 knots”
2MF Location “2 nautical miles from final”
090 Threshold wind direction “90 degrees”
12 Threshold wind speed “12 knots”
No * is shown, therefore a windshear alarm outside the network area is not
indicated.
In the example, line 2 provides the following information:
10D Operational runway “10 Departure”
WSA Windshear alarm
20K- Estimated wind speed loss “20 knots”
RWY Location “Runway 10D”
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090 Threshold wind direction “90 degrees”
12 Threshold wind speed “12 knots”
Since no * is displayed, no windshear alarm outside the network area is
indicated.
Lines 5, 6, 7 and 8 are unused in this example.
As the system is operating normally, line 9 remains blank.
Line 10 displays the following information:
CF Centrefield location
090 Wind direction “90 degrees”
16 Centerfield wind speed “16 knots”
G22 Centerfield wind gusting to “22 knots”
1046 System time 1046 UTC
ALM OFF Audible alarm is switched Off
2.1.7.2.3 Operation
During normal operation (no windshear alarms) the AAD displays Runway
Identification, Wind Direction and Wind Speed for each selected runway.
The bottom line of the display (line 10) shows Centerfield Wind Direction &
Speed, Gust Wind Speed, System Time (UTC) and Audible Alarm Status.
Figure 2-8 An AAD in normal operation, showing no alarms.
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When a wind threshold is reached, the information line associated with the
affected runway(s) will flash red for a predetermined period of time. The
information displayed will now include data relating to the alarm condition, as
described in section 2.1.7.2.2.
Figure 2-9 An AAD highlighting a “Microburst Alert” for runways 10A
and 28D, by flashing red for a predetermined period of time.
When the “highlighting” period has expired, the AAD will stop flashing and
display steady text information relating to the alarm condition.
Figure 2-10 An AAD displaying “Microburst alarm” information after the
highlighting period has expired.
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2.1.7.2.4 Runway Threshold Configuration Display
The Runway Threshold Configuration Display is an object that can be placed
on a screen containing an AAD. A drop-down list allows the user to select and
view any available display configuration.
Figure 2-11 AAD Configuration Drop-down List
Each configuration determines which runway windshear threshold
information is to be displayed on the AAD.
For example, if the user selects a configuration that shows the windshear
information for “Runway 10 Approach and Runway 28 Departure”, then the
AAD will only display windshear information relating to those two zones. The
other display lines will be left blank. This saves the ATC from having to
distinguish between their runway windshear thresholds and the rest of the
airport.
If “All Runways” is selected, then windshear information relating to all the
runways is displayed.
Once a configuration has been selected, this is shown on the Runway
Threshold Configuration Display as illustrated below.
Figure 2-12 Display Configuration Selection
2.1.7.3 Graphical Alarm Display Screens (GAD)
The GAD display consists of two separate screen objects, an AAD screen
object (described above) and a separate map display. Buttons at the bottom
of the screen allow selection of different background bitmaps as appropriate.
Because the map is a screen object, the GAD can be displayed with other data
as well, such as the Supervisor’s AAD Selector (described below).
The Almos Map display (GAD Object) consists of a background bitmap and
numerous graphical objects overlaid upon this background.
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Arrows
Arrows point where the wind is blowing ‘to’ by default. Sensors that are
marked out of scan or in a fault condition appear as a red circle.
Wind Speed Box
Next to each arrow, a floating wind speed box shows the current wind speed.
The box moves with the arrow in such a way so as to not obscure the arrow
itself.
Edge/Triangle Alarm displays
During divergence/convergence detection, a red line (shaded based on
strength) depicts the area in which the wind shear is being detected.
Combined with the AAD object already on screen, this provides an excellent
windshear warning system and situation display.
Figure 2-13 LLWAS Map (Normal Operation)
Triangles are displayed as shaded red areas. The degree of shading reflects the
intensity of windshear within that area.
A typical LLWAS Map showing areas affected by windshear is shown below.
Figure 2-14 LLWAS Map (Showing Windshear)
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2.1.8 Interfaces
The Almos LLWAS system offered supports interfaces of up to 256 remote
stations using the communications methods (radio and landline) described
herein.
Due to the client/server network nature of the Almos LLWAS system, the
number of supported display terminals, system consoles and printers is
practically unlimited. The provided network hub is may be linked to any
number of additional hubs, increasing the supported number of workstations
significantly.
A dedicated port can be set up to send data to an external network such as
the Official Airport System network. Using TCP/IP, the external connection can
access real-time data from the MetConsole server. This may be used for
connection to third party software of for remote diagnostics and data display.
This interface is called the External Data Interface and the default format is
described in detail below.
2.1.8.1 External Data Interface
The Almos LLWAS system gets data in from the wind sensor stations, from
threshold sensor stations and, in some cases, from other sensors around the
airport. This data is distributed to many modules in the system and various
calculations are performed on it.
MetConsole also makes the data from the LLWAS system available to external
users.
2.1.9 Algorithm Implementation
Almos LLWAS MetConsole uses an efficient LLWAS algorithm
implementation designed to perform all required calculations in a minimum
amount of time.
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F
i
g
u
r
e
1
5
-
LLWAS Data Input
Averaging (RC/Linear) is performed on the remote stations. RC and Linear
averaging constants are transmitted to the remote stations based on values
configured on the server. These configuration constants then can be updated
at any point without visiting the remote sites. Processing averaging on the
remote sites also means that only the final averaged values need be
transmitted to the master station, reducing transmission time and increasing
reliability.
Wind Gust computation is also partially computed
on the remote stations. Remote stations report 10
second average information to the master station,
which in turn computes a 10 minute gust using
the UAL Wind Gust Algorithm attached to this
document.
On the master station server, a timer calls various
components of the software every second. As
each component has an associated time period, it
can determine if the current ‘tick’ is appropriate
for executing its associated process.
For example, LLWAS has an associated ten second
time period. Even though LLWAS is called every
second it will only execute on the tenth second –
thus keeping in time with the LLWAS system
cycle.
Timer TICK
Threshold Sensor Interface
Master Station Controller(s)
Process MODULES
Arithmetic (Wind Gust etc)
UCAR LLWAS ALGORITHM
1. Data Preparation
2. Network Statistical Analysis
3. Divergence Analysis
4. Alert Analysis
5. Format Messages
SPES DQA
1. Bin Data per cycle
2. Process Periodic SPES Reports
DATABASE LOGGING
SERVER REPLICATION
DISPLAY
WIND
REMOTE
STATION LDL
MASTER STATION SERVER
KEYBOARD
& MOUSE
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Each process is designed to operate extremely efficiently, taking only a
number of milliseconds to complete. Therefore, all items executed by the
timer are completed well in advance of the next timer ‘tick’.
2.1.9.1 LLWAS Algorithm Functions
2.1.9.1.1 FAA Gust
Parameters
1. Time (seconds) of first variable average
2. Variable name
3. Gust calculation time period (seconds)
4. Gust variable name
5. Calculation intervals (seconds)
6. Peak_Wind_Threshold
7. CF_Threshold
8. Gust_Threshold
9. Calm_Threshold
The gust algorithm uses wind measurements from an LLWAS centrefield
station to determine gust wind speed.
The algorithm determines peak wind speeds over a 10-minute period and
compares these with a 2-minute average wind speed.
This is accomplished in two stages:
1. Wind speeds during the last minute that exceed the 2-minute centerfield
average by 5 knots are recorded, in order to determine a peak wind
speed.
2. Recorded peak winds measured over the past 10 minute period are
compared with the centerfield average wind speed, to determine a
maximum peak wind speed (gust).
The calculated gust wind speed is displayed for 10 minutes, unless the
maximum peak wind measurements fall to within 3 knots of the centerfield
average wind speed.
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2.1.9.1.2 LLWASAAD
Parameters Units
1. Wind direction “D” degrees
2. Wind speed “S” knots
3. Gust knots
This function calculates a gust string that displays centerfield wind data at the
bottom of the AAD.
The string format input determines the order and content of the gust string
output e.g. a string format of the form CF<DIR><SPD><G><GUST> would
produce the following centerfield wind display (<G> adds the character “G” if
a gust is currently valid):
Wind direction – Average wind speed – Wind gust speed
The gust threshold is a value set above the average wind speed. When the
calculated “peak” wind exceeds the average by more than the threshold, then
a gust value is displayed on the AAD.
2.1.10 Archiving / Playback
The Archiver application is used to independently store data from the remote
MetConsole servers. Two optional features are often installed with the
Archiver to provide a full archive & replay system:
• Media backup
• Data replay
One of a number of media backup options is available (i.e. Tape, optical disk,
removable disk drive).
The archiver application normally runs in the Windows task bar, and as such
is usually available from the bottom right of the screen (depending on any
personalised settings that may have been set up).
The displayed icon may change depending on the state of the archiver:
The archiver is connected to the hot server, and idle.
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The archiver is currently receiving data from the hot server.
The archiver is unable to connect to the hot server, and is retrying.
To access the archiver application, right-click on the icon (whichever icon is
displayed) to display a menu.
Click on Open Main Window to open the archiver application screen. Click
on Close to close the archiver, or click on About to view the archiver copyright
and version information.
Each operation may be configured to use a password, and displays a security
login box such as the following:
Enter your username and password to access the software.
The Main Window, once opened, is displayed similar to the following:
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In addition to the action buttons in the main window, four additional status
fields are given:
1. Archiver Status: This indicates the current state of the archiver application.
2. Instructions Pane: This provides information on the current state, and
available options, if appropriate.
3. Connection State & Progress Type: This provides a text message indicating
the state of the connection. If the archiver is performing a lengthy
operation, this changes to indicate the type of operation being displayed in
the Progress Bar (4).
4. Progress Bar: When performing a lengthy operation, this changes to
indicate the current state of the operation.
The action buttons present are:
Archive: Click this button to resume archiving online data from
MetConsole. Stop pauses the online data archive.
Reload: Reloads (restores) data from removable media storage. See
Reloading Data below.
Re-Play: Replays the currently available data. See Replaying Data
below.
Backup: Manually Backs up data to the removable media storage.
The archiver goes idle during this process.
Report: Reports on the most recent media operations. This is a
third party report provided by the media software vendor.
About: Displays the copyright message and version information.
Stop: Stops the action currently being carried out. Not
available when Idle.
2.1.11 Maintenance
NOTE: Comprehensive Maintenance sections exist in both the WAWS
Hardware Manual and the MetConsole Reference Manual.
Described below is an overview of the type of maintenance tools that are
available to the technical staff.
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2.1.11.1 Master Station Maintenance Screens
A comprehensive set of maintenance and diagnostic screens are available to
the user. These features are fully described in the BITE section of this
document
The ‘Maintenance’ windows will only be accessible by the Maintenance user
and is not required for ATC users.
2.1.11.1.1 Help
Extensive use of Tool Tips is made throughout the system. Positioning the
mouse pointer over most controls will display a label with information about
the control or the item of data being displayed.
Example of tool tips
Pressing F1 will bring a context sensitive Windows Help file with help, tips,
and guidance and specific tasks.
Extensive on-line help is available
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Right clicking on any variable brings up more information about the point
including details about any fault status.
2.1.11.1.2 Alarms and Events
The system monitors all incoming weather variables and can detect a variety
of faults in the data stream. Data faults include:
• Primary/Secondary Server Failure.
• Communications faults.
• Sensor faults.
• Missing data.
• Value too high or too low.
• Value higher or lower than airport operating maxima.
• Value jumping too rapidly from value to value
• Value “frozen” within a small range of value.
Acceptable ranges can be set arbitrarily on any point. And any test can be
omitted. As alarms occur they are printed on the system printer, stored in the
Windows NT event log, stored in a database file, and if the alarm or event
requires acknowledgment is placed in an alarm list in a toolbar the server.
The current alarm list is displayed in a toolbar.
2.1.11.1.3 Technicians functions
There are a number of trouble shooting screens built in to the system to
assist technicians. The “Technical Reference Manual” provides
descriptions of how to use these screens.
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Terminal data for sensor interface
2.1.11.1.4 GPS Time Sync
Our time synchronisation system reads the external time messages and
compares the time to the server’s clock. If the time is inaccurate then the
software will:
1. Remove or insert milliseconds off each tick of the clock until the PC time
matches the external clock, and the server becomes in sync.
2. Compute the exact inaccuracy of the PC clock compared to the reference,
and then remove or insert milliseconds from each clock tick to proactively
ensure that the time remains in sync.
Because we are always making minor changes to the time there cannot be
“jumps” in the data set caused by the time changing rapidly. The unique
proactive correction of the PC clock ensures that accuracy is maintained even
if the time source is lost for an extended period of time.
The time setting functions provide a facility for entering the time in the
absence of an external time source. These allow the user to enter the time
on the primary server; the time is simultaneously broadcast across the
network, with each PC updating its time as required.
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All system functions are timed relative to the server’s PC clock, and all other
PCs time is set to match the server’s time. Each master station computer is
fitted with a removable, rechargeable battery backup on the internal clock,
ensuring maximized lifetime on the real-time clock components.
2.1.11.1.5 Watchdog
Almos supplies watchdog hardware that monitors all system operations. An
independent hardware card installed in the machine monitors the MetConsole
software. In the event of any failure of hardware, operating system, or the
application program, (which prevents normal operation) the PC is completely
reset. This substantially reduces the number of fault callouts and significantly
improves the MTTR.
2.1.11.1.6 Remote Access
We provide a remote dial in server utilising Microsoft Remote Access Service
(RAS). This facility permits access to monitoring and diagnostics of the system
by Almos. This port can also be used for centralised monitoring of the system.
This can also be used to remotely upgrade or reconfigure the system. Of
course this feature is password protected and can be enabled and disabled as
required.
2.1.11.2 Built–In Test Equipment - BITE
In an airport environment, due to the requirements to keep repair and
downtime to the absolute minimum, an automatic failure detection and
isolation system referred to as built-in-test equipment (BITE) is implemented
on all equipment. BITE functions are primarily performed by software
resources.
The primary objective of BITE is to correctly detect system malfunctions and
accurately fault-isolate to a single replaceable unit so that maintenance staff
with a minimum of training are able to perform this function. Failures
undetected by BITE will be kept to a minimum. The BITE will be capable of
isolating faults down to LRU level in most fault cases.
2.1.11.2.1 BITE Requirements
BITE functionality is integrated into the different equipment in order to avoid
external test equipment for stimuli and measuring purposes. BITE functions
do not interfere with the operational of the system.
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2.1.11.2.2 BITE Functions include:
• Intelligent wind sensor is offered with BITE functions. Results are
continuously received and checked by the Remote Station in the form
of Status messages.
• *Sensor data is checked both for data format errors and for data quality
errors. Error checks include sampling the status information provided
by the sensors.
• Remote station serial interface to Wind Sensor can be tested by
executing a loop-back command that results in receiving characters
transmitted on the Tx line. This way serial interface errors can be
differentiated from sensor errors.
• *Remote station basic operational parameters, such as availability of
mains supply, internal enclosure temperature, battery status, EPROM
CRC etc are monitored and the results are reported back
• Full Remote Station testing facilities, including built-in software and
hardware diagnostic functions, are available through a Maintenance
Interface Port. Operational status, current sensor data and raw sensor
data can be displayed.
• Radio BITE features are available through a serial interface.
• *Remote Station radio communication quality can be tested using a
built-in Bit Error Rate Mode. This mode can be activated by a remote
command.
• Communication ports are tested by heart beat packets sent between
computers
• Analog signals are tested to cross acceptable low and high levels
• Watchdog cards in all PCs and Remote Stations test fatal system
errors. Automatic restarts are generated after error detection.
• RAM memory is tested in PCs and the Remote Stations at system
reset.
• All memory components in the Remote Stations are checksum tested at
system reset.
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• Software execution integrity is tested and fault information including
Detailed CPU instruction information) logged prior to watchdog
intervention.
Note: BITE functions marked * are sufficient to satisfy the latest FAA
LLWAS Remote Station BITE requirements. Additional BITE was added by
Almos to further simplify installation and maintenance.
2.1.11.2.3 Features:
Unit Fault
detectio
n
Isolation False
Alarm
Sensor Yes Automatic No
Remote
Station
Yes Automatic Communication link
fault can be isolated by
communication LEDs
No
Server
computer
Yes Automatic. Communication
link fault can be isolated by
communication LEDs on
modems and network hub.
No
Workstation Yes As above No
Printer Yes Semi-automatic, as provided by
manufacturer (Status display
indicates LRU fault).
No
2.1.11.3 Site Performance Evaluation System (SPES)
A very attractive module is the Site Performance Evaluation System (SPES). This
software module runs a Data Quality Analysis algorithm developed by MIT’s
Lincoln Laboratories to analyse the performance of the wind sensors in real
time. The algorithm compares the raw values of all sensors to the network
mean and then makes judgments about possible siting problems or accuracy
problems with each sensor.
Provided as a standard item with Almos LLWAS systems, is an additional PC
for the purpose of running and displaying SPES Data Quality Analysis.
The additional SPES workstation provides technical monitoring facilities for
network data quality analysis. An additional MetConsole component
(Module) is installed and configured on the server pair for processing of SPES
data.
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2.1.11.3.1 Introduction
The integrity of wind data received from each remote weather station is
evaluated by the SPES. This is achieved by constantly comparing the wind
speed and direction information received from each station with the overall
network mean values.
Note
For a data poll to be valid for SPES, there must not be a
windshear or microburst indicated on the LLWAS system.
Also, the wind speed must be greater than 3 metres per
second (6 knots) at the time of the poll.
2.1.11.3.2 Integrity Evaluation
The SPES wind data evaluation is based upon two separate, but related, tests.
These are:
• Wind speed
• Wind direction
2.1.11.3.2.1 Wind Speed Test
Wind speed data is collected from all the weather station sensors and a mean
value calculated. The ratio of variation with the mean value is then calculated
for each individual weather station.
The calculated variation ratios are stored in groups, based upon wind
direction. This enables the system to determine whether the variations in wind
speeds for a particular station are related to a few directions only, or all
directions.
Sensor status in relation to wind speed data is given by the following SPES
messages:
• Sheltering
• Frictional drag or sensor situated too low
• Wind channelling.
• Sensor situated too high
2.1.11.3.2.2 Wind Direction Test
Wind direction data is collected from all the weather station sensors and a
mean value calculated, similarly to wind speed. Wind directions are compared
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to the mean wind direction for the network and the mean variation is stored.
The variations are stored in groups of similar variations for each station.
If the percentage of ratio differences is greater than a predetermined figure
over a certain time, it may be determined that there is a problem with the
sensor, or that the orientation of the station is not correct.
Sensor status in relation to wind direction data is given by the following SPES
messages:
• Sensor orientation incorrect
• Electrical grounding fault
• Loose mounting or sticky wind-vane bearings
2.1.11.3.3 SPES Screens
The SPES has two types of screen:
• A” Site Performance Evaluation System” screen
• (Shows the general status of all weather stations)
• A “Station Analysis” screen for each individual weather station in
• The LLWAS system
• (Provides more detailed information about each weather station)
2.1.11.3.3.1 “Site Performance Evaluation System” Screen
This screen shows the wind speed and wind direction status of each weather
station on the system.
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2.1.11.3.3.2 “Station Analysis” Screen
By clicking on a Details button on the “Site Performance Evaluation System”
screen, specific information about a particular station can be viewed on its
Analysis screen. A typical Station Analysis screen is shown below.
Figure 2-16 SPES “Station Analysis” Screen
A station’s Analysis screen displays data integrity information about its wind
sensors on 3 graphs and a wind gauge. Each graph provides the user with a
different perspective on the data received from the weather station.
Each Analysis screen also has a Windrun gauge and Wind Rose display related
to that station. Although not actually part of the SPES, they provide useful
wind related information to the user.
The Windrun gauge plots the amount of wind in meters per second,
measured by the sensor, on a rotating time axis. The axis is configurable, but
set to 24 hours for Chaing Kai Shek airport.
The Wind Rose provides a real-time graphical indication of wind direction and
speed in accordance with the LLWAS system 10-second wind data.
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Speed Ratio over Direction Graph
This graph shows the sensor performance as a ratio to the network mean
value, over the last large sample of polls. This ratio is represented on the bar
graph horizontal axis for every direction with a vertical incremental scale of
0.00 to 2.00.
In a “perfect” system a weather station would return a value that is the same
as the network mean, thus registering a ratio of unity. The graph would then
plot a value of 1.00 for all directions.
Difference from Mean (Wind Gauge)
The wind gauge displays the ratio shown on the “Speed Ratio over Direction
Graph” on a rotating axis. The gauge axis is the same as the graph, i.e. 0.00
to 2.00.
For the “perfect” system referred to above, the sensor would display a ratio of
1.00 in all directions and plot a circle halfway into the gauge. If a calculated
ratio is low, then the gauge plot will be nearer the centre for that direction. If
the ratio is high then the plot will be nearer the outside of the gauge for that
direction.
In practise, wind speed ratios can differ from 1.00 for various reasons. For
example, if all the ratios are low his may indicate a wind speed sensor bearing
problem causing it to rotate slowly.
Both the “Speed Ratio over Direction Graph” and the “Difference from
Mean” wind gauge indicate to a user if there is an obvious problem with a
station sensor and whither the problem is directional or not.
Speed Ratio Frequency Graph
This graph shows the ratio of the weather station wind speed sensor data
average against the network wind speed average, for all directions.
A “perfect” system would register a ratio of 1.00 in all directions.
Direction Difference Frequency Graph
This graph shows the percentage difference between the weather station’s
sensor direction average against the network direction average. A difference
of ±5º is considered acceptable.
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2.1.11.4 Installation and Maintenance Tools
2.1.11.4.1 Communications Testing Tools
Due to the fact that the entire communication system is based on digital
radios and a digital protocol, all communication analysis is done in software.
Other devices are not needed to isolate faults and monitor the
communications however the IFR 1600 is quoted as an option.
2.1.11.4.1.1 Communication Service Monitor
The equivalent of the Communication Service Monitor is a software package
that is delivered with the digital radios. Please see the Maintenance section in
the WAWS Installation and Maintenance Manual.
2.1.11.4.1.2 Serial Communication Analyser
The Technicians Screens in the MetConsole software running on the Master
Station Servers may be used to analyse the digital communication traffic.
These screens are described in the Maintenance Section of the MetConsole
Reference Manual.
2.1.11.4.2 Installation Tools
The following is a list of the tools which will be provided for the installation
and servicing of the LLWAS equipment :
1) Adjustable Spanners-
• 6"
• 10"
2) Crimp Tools-
• Suitable for Bootlace Ferrules
• Suitable for crimp lugs used
• Suitable network RJ45 plugs (8 way 8 contact)
• Suitable for RF connectors used
3) Drill Bit Set -
4) Drill – Battery type
5) Hexagon Key Set - Imperial Sizes
6) Pliers -
• Long Nose
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• Linesman’s
• Sidecutters
7) Knife with snap-off blades
8) Scissors
9) Screwdrivers -
• 3.5mm Flat Blade
• 5mm Flat Blade
• No.0 Posidriv
• No.1 Posidriv
• No.2 Posidriv
10) Weller Soldering Iron & Solder
11) Wire Strippers
12) 60mm Mini Bench Vice
2.1.12 System Modes (States)
The LLWAS software runs in a number of states based on the availability of
remote stations in the network, and the presence of maintenance activities
being carried out on the system. These states are described in detail below.
2.1.12.1 Real Time Normal
All remote stations and text displays (AADs) are fully operational.
2.1.12.2 Real Time Degraded
At least one remote station is not operational and at least a specified number
of remote stations are operational. This specified number is a parameter
defined in the CAA furnished configuration files. The system is also in the
Real Time Degraded state when fewer than all of the text displays (AADs) are
operational.
2.1.12.3 System Support
Fewer than a specified number of remote stations have been operational for a
period of time. The specified number of remote stations is a parameter
defined in the CAA furnished configuration files. The period of time is
defined by the algorithm's ability to fill data gaps. (Refer to the algorithm
specification in Appendix A)
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The system is also in the System Support state whenever the system
determines that at least one of the configuration files is invalid or whenever
other serious unexpected system problems are encountered.
2.1.12.4 Initialization
The system state during the period of time required for the system to start up
from the powered off condition until it is processing adequate data to start
displaying wind data, wind shear and microburst alerts (as defined in the
algorithm specification).
The system shall complete its initialization procedures and restore itself to real
time operational capability within five (5) minutes (MAXINIT) after the
restoration of the facility power sources.
During initialization wind and windshear alert information is not displayed on
the Text Displays (AAD).
2.1.12.5 Off
No power is being provided to the master station controller.
The Text Displays shall indicate that they are no longer receiving data from the
LLWAS master station.
2.2 Configuration File
All MetConsole stations are configured through a single shared configuration
database. This database file contains configuration information pertaining to
the role of each station on the network (primary server, secondary server,
archiving PC, SPES workstation, operator workstations, displays etc). In
addition, the configuration database contains LLWAS parameters contained in
the ACF, SPES thresholds & parameters, DCF configurations and other
configuration data.
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Figure 17 - LLWAS System Configuration (Typical)
The advantage of this shared configuration database approach is that systemwide
configuration can be achieved through reconfiguration of a single
central source file. The configuration database is centrally stored and changes
to this file are automatically integrated by MetConsole instances operating
across the network.
MetConsole operates through ODBC, Microsoft’s Open Database Connectivity
technology. ODBC makes the choice of database dependant only on system
requirements. Microsoft Access can be used; likewise Oracle 8, SQL Server 7
and other technologies can be used. The configuration database is accessible
using common tools (i.e. Microsoft Access) and providing a simple and easy to
learn interface for all users.
This open architecture does not limit the MetConsole system to any single
database technology. This advantage allows Almos MetConsole users to
operate a database that best suits their unique individual requirements, rather
than a single database that is not perfectly suited to their situation.
The final database format is yet to be determined; the final database format
will be chosen based on the overall performance of the system and will be
formally tested and approved at the Factory Acceptance Test.
Changes to ACF (Airport Configuration File) and DCF (Display Configuration
File) are implemented directly in the configuration database, which is in turn
secured via Windows NT security (only accessible from the master station to
authorized users). Facilities are provided for the import of these files, allowing
easy implementation of future siting changes.
SYSTEM CONFIGURATION (SCF) and
MAINTENANCE CONFIGURATION
(MCF) (Averaging constants,
Displays, Parameters, etc)
AIRPORT CONFIGURATION FILE
(ACF)
DISPLAY CONFIGURATION FILE
CONFIGURATIO
DATABAS
(METCFG.MDB
AAD DISPLAY
SYSTEM
INPUT DEVICE
ARCHIVE STATION
KEYBOAR
D &
MOUSE
AAD DISPLAY
SYSTEM
INPUT DEVICE
AAD DISPLAY
SYSTEM
INPUT DEVICE
RAW CONFIGURATION FIL ES
& PARAMETER S
SHARED
(BOTH
LLWAS MetConsole
Overvie
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2.2.1 ACF
The Airport Configuration File (ACF) shall be created by Almos Systems based
on the results of the Site Survey and expertise and software from NCAR. This
procedure has already been successfully performed at two Phase III LLWAS
Installations.
2.2.2 DCF
A standard Display Configuration File (DCF) shall be created by Almos
Systems. This may be altered to suit the customers individual needs.
2.2.3 MCF, SCF
The MCF (Maintenance Configuration File) and SCF (System Configuration
File) are standard parts of the LLWAS Configuration database. They may be
altered but there is generally no need to do so.
3. Reliability, Maintability, Availability (RMA), and
Supportability
3.1 RMA Characteristics
This section describes Almos RMA performance, including but not limited to
Mean Time Between Failure(MTBF), Mean Time Between Corrective
Maintenance Action(MTBCMA), Mean Time Between Critical Failures(MTBCF),
Built in Test and Fault Isolation capability, Mean Time To Repair(MTTR), and
inherent availability.
3.1.1 Mean Time Between Failure (MTBF) / Mean Time Between Critical Failures
(MTBCF)
The equipment offered, including computer software, have been proven in a
number of airport installations. They are of high quality, off-the-shelf and
commercially available, and are capable of operating continuously with a high
degree of reliability. Particulars of existing installations using the type of
equipment offered are attached.
The most critical component in the system is the central computer. The
solution offered is based on a Hot Standby solution, which has been used in a
number of AWOS systems.
The failure rates of all components were considered. Note that neither
Compaq nor IBM would publish MTBF figures for their workstations or servers
(even though we are a Compaq distributor). Consequently we have used
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estimates based on our experience with this equipment. Assuming that the
MTBF of the PC is as low as 5,000 hours (about half a year) and assuming that
the MTTR for the PC is one hour (swapping with spares). In this case
duplicating the server will increase the MTBF beyond the lifetime (20 years) of
the system.
The sensor interface units offered are identical with the ones used in the
Almos Automatic Weather Stations. These stations are currently used by the
Australian Bureau of Meteorology. Almos has been the exclusive supplier of
Automatic Weather Stations to the Australian National Weather Network
since 1993. Based on official service records MTBF calculations are shown
below (Error! Reference source not found. MTBF Evaluation), which show
MTBF better than 30 years.
On the basis of above considerations the Mean Time Between Critical Failures
(MTBCF), which would stop operation of the Central Computer or one of the
Remote Stations is larger than 20 years. Mean Time Between Failures (MTBF),
which includes wind sensor errors and potential display errors is estimated to
be 10,000 hours.
3.1.2 Mean Time Between Corrective Maintenance Action (MTBCMA)
The only component that requires regular maintenance in the proposed
system is the wind sensor. MTBCMA = 1 year
3.1.3 Built in Test and Fault Isolation capability
Due to the requirements to keep repair to the absolute minimum, the impact
on operational readiness and the maintenance concept adopted, automatic
failure detection and isolation, referred to as built-in-test equipment (BITE) will
be implemented on all equipment and monitored. BITE functions are mostly
performed by software resources. The primary objective of BITE is to correctly
detect system malfunctions and accurately fault-isolate to a single replaceable
unit so that maintenance staff with a minimum of training is able to perform
this function. Failures undetected by BITE will be kept to a minimum. The
BITE will be capable of isolating faults down to LRU (SRU) level in at least 80%
of fault cases.
BITE function will be integrated into the different equipment in order to avoid
external test equipment for stimuli and measuring purposes. BIT functions will
not interfere with the operational of the system.
BITE functions include:
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• Sensor data is checked both for data format errors and for data quality
errors. Error checks include sampling the status information provided by
intelligent sensors.
• Communication ports are tested by heart beat packets sent between
computers
• Fatal system errors are tested by Watchdog cards in all PCs and Remote
Stations. Automatic restarts are generated after error detection.
• RAM memory is tested in PCs and the Automatic Weather Stations at
system reset.
• All memory components in the Remote Stations are checksum tested at
system reset.
3.1.4 Mean Time To Repair (MTTR)
The computer equipment will be repaired by swapping complete units with
spare, which will take average 15 minutes.
Remote Stations will be repaired by swapping cards. Using the advanced
Almos Diagnostic Tools faults can be diagnosed and cards swapped within 30
minutes plus traveling time.
Sensors will be repaired by swapping them with spares. Due to the fact that
access to some sensors is cumbersome the repair time would take one hour
average.
Unit Fault
detection
Isolation False Alarm
Sensor yes The system will detect most
sensor faults
no
Remote
Station
yes As above. Communication link
fault can be isolated by
communication LEDs
no
Server
computer
yes Automatic. Communication link
fault can be isolated by
communication LEDs on modems
no
Display
Workstation
yes As above no
Printer yes Automatic no
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3.1.5 MTBF Evaluation
3.1.5.1 Purpose
The purpose of this evaluation is to calculate the reliability of the Almos
supplied hardware.
3.1.5.2 References
Collection of reliability, availability and maintainability data for electronics and
similar engineering use - AS2529, 1982
Presentation of reliability data on electronic and similar components (or parts)
AS2530, 1982
Reliability and maintainability - Introductory guide - AS3930, 1992
Reliability Prediction Procedure For Electronic Equipment - Bellcore TR-NWT-
000332, Issue 4, September, 1992.
3.1.5.3 Definitions
MTBF - (Mean Time Between Failure) - Average time (expressed in hours) that
a component works without failure. It is calculated by dividing the total
number of failures into the total number of operating hours observed. Also,
the length of time a user may reasonably expect a device or system to work
before an incapacitating fault occurs.
MTTF - Related acronym (Mean Time To Failure) which is frequently used
interchangeably with MTBF.
3.1.5.4 Approach
Almos established via test data obtained under the operating environment
required for the REMOTE STATION hardware and by analysis of existing data,
that the supplied hardware will meet the mean-time-between failure (MTBF)
of 30,000 hours.
3.1.5.5 Reliability Data
The data used in this analysis was extracted from the population of equipment
installed for the Australian Bureau of Meteorology and relates to similar
hardware operating under similar conditions to those proposed for the
REMOTE STATION.
Upon request, a spreadsheet is available which provides the raw data used to
obtain the figure shown below as Total Hours.
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Data Item Value Used in Calculations
Oldest Unit (Years) 3.6 Yes
Machine Population 222 Yes
Total Hours 3,162,240 Yes
Failures 11 Yes
NFF 0 No
User Caused 3 No
Table 1 - Field Failure Data
3.1.5.6 Reliability Calculations
MTBF is Mean Time Between Failure and is typically expressed in hours. The
hours are calculated by dividing the total number of failures into the total
number of operating hours observed. For Almos, MTBF represents the average
number of hours a field population will work before a failure occurs.
3.1.5.6.1 General Assumptions
3.1.5.6.1.1 User caused failures
Any failure that was directly attributed to user negligence or abuse has been
shown in Table 1 but has not been included in the MTBF calculation.
3.1.5.6.1.2 No fault found
Units returned are subjected to extensive testing before release back to the
customer. Units with “No Fault Found” have been shown in Table 1 but have
not been included in the MTBF calculation.
3.1.5.6.2 Method 1
3.1.5.6.2.1 Basis of Calculation
Age of units - The population of equipment used in this analysis was supplied
over a period of time. It is assumed that the rate of supply of equipment is a
constant and the average age of all units is therefore half the age of the
oldest unit.
Operating Hours - The equipment is assumed to be in service for 100% of the
time. (24x7x365)
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3.1.5.6.2.2 Calculation
MTBF =
MTBF = = 318,227 hours = 36.3 years
3.1.5.6.3 Method 2
3.1.5.6.3.1 Basis of Calculation
Actual Operating Hours - The population of equipment used in this analysis
was supplied over a period of time. The actual year and month of supply for
each individual unit was used to obtain the age of the equipment. This was
used to calculate the total hours since supplied. (Refer to attached
Spreadsheet)
Operating Hours - It was assumed that each item was not installed for one
month after being supplied and thereafter has been in service for 100% of
the time. (24x7x365)
3.1.5.6.3.2 Calculation
MTBF =
MTBF = = 272,945 hours = 31.2 years
3.1.5.7 Results
The lowest figure provided by the two methods used has been selected as the
more accurate, being based on actual dates rather than an assumption about
the linearity of supply.
MTBF = 31.2 Years.
3.2 Supportability
The system has many built in test (BITE) and diagnostic features, which make
the maintenance of the system very efficient for trained personal.
Remote diagnostics means that engineers from Almos Systems headquarters
may dial into the system and analyse any faults that are being reported.
The Site Performance Evaluation Subsystem which is offered as a standard
tool, aids in the long-term accuracy of the LLWAS system.
Local support and warranty service is usually provided through appointed
subcontractors