Airbus A321-231, G-MIDJ 事故分析

航空

游客，如果您要查看本帖隐藏内容请回复

航空

1
Airbus A321-231, G-MIDJ
Contents
Report Information ........................................................................................................2
Synopsis ...........................................................................................................................2
History of the flight ........................................................................................................3
Meteorology ....................................................................................................................5
Satellite information................................................................................................................. 6
The radar picture ...................................................................................................................... 8
Flight Recorders...................................................................................................................... 8
Passenger cabin activity`........................................................................................................ 13
Aircraft damage............................................................................................................14
Weather radar system..................................................................................................15
Weather radar system tests..................................................................................................... 15
Operation and limitations of the weather radar equipment.................................................... 15
Weather radar training ........................................................................................................... 16
Recent developments....................................................................................................17
Flight Management Guidance System (FMGS) ........................................................17
Discussion.....................................................................................................................18
Conclusions ...................................................................................................................20
Follow-up actions................................................................................................................... 20
Recommendation..........................................................................................................21
Safety Recommendation 2004-47.......................................................................................... 21
Airbus A321-231, G-MIDJ
2
Report Information
AAIB Bulletin No: 6/2004 Ref: EW/C2003/05/03 Category: 1.1
INCIDENT
Aircraft Type and
Registration:
Airbus A321-231, G-MIDJ
No & Type of Engines: 2 V2533-A5 International Aero
turbofan engines
Year of Manufacture: 1999
Date & Time (UTC): 26 May 2003 at 1543 hrs
Location: In the cruise at FL340, 70 nm
south-east of Vienna
Type of Flight: Public Transport
Persons on Board: Crew - 8 Passengers - 213
Injuries: Crew - None Passengers - None
Nature of Damage: Significant damage to radome,
flight deck windows, stabiliser
leading edges and engine
nacelles
Commander's Licence: Airline Transport Pilot's
Licence
Commander's Age: 42 years
Commander's Flying
Experience:
11,457 hours
(of which 262 were on type)
Last 90 days - 184 hours
Last 28 days - 49 hours
Information Source: AAIB Field Investigation
Synopsis
The aircraft was in the cruise at FL340 approximately 70 nm south-east of Vienna when it
encountered an area of severe turbulence and hail. Some of the flight deck windows became crazed
and other areas of the airframe suffered extensive damage although this was not apparent to the crew.
The aircraft made a precautionary descent to FL230, in accordance with the required abnormal
procedures, and continued the flight to its destination of Manchester. The crew had no indication or
warning that the aircraft was about to enter an area of severe turbulence, associated with the upper
levels of a Cumulo-nimbus cloud. When they had been using the weather radar to check the route
ahead of the aircraft, sometime before the encounter, the radar returns appeared benign.
Airbus A321-231, G-MIDJ
3
History of the flight
The crew reported for duty at Manchester at 0555 hrs to operate a return flight to Larnaca in Cyprus.
The only weather of note on the 'Sigmet' chart for the outbound sector was Cumulo-nimbus (Cb)
cloud activity over the Italian Alps. During the outbound flight no turbulence was experienced and
the only Cb activity observed by the crew was over Turkey, to the north of their route. Towering
Cumulus (Cu), however, was seen to be building over the northern part of Cyprus. This activity and
the Cbs were monitored by the crew on the aircraft's weather radar display. The radar appeared to be
functioning correctly and displayed the type of returns the crew would have expected from such
weather. The aircraft landed at Larnaca at 1135 hrs after an uneventful flight.
The aircraft was refuelled to full tanks and, after a one hour 'turn-round', departed Cyprus for
Manchester with the First Officer (FO) as the Pilot Flying (PF). The commander's duties, as the Pilot
Not Flying (PNF), were the management of the navigation and RT communications. The Standard
Instrument Departure (SID) and climb to cruising altitude routed the aircraft to the west of the cloud
building up on the north side of the island. The intensity and extent of this cloud was monitored by
the crew on the weather radar.
The aircraft was initially cleared to 8,000 feet but before reaching that altitude, a further clearance to a
cruising level of FL340 was issued and the climb continued. The cabin crew were cleared to
commence the cabin service and the aircraft levelled at FL340. The pilots had been monitoring Cb
activity, on the weather radar, to the east of their track and approximately two hours into the flight
they noted some isolated Cb activity ahead of the aircraft to the right and left of their track. The Cb
activity to the right of track was minor and isolated. Cb activity to the left of track was less intense.
The radar was set to a scale of 160 nm and with no significant returns ahead and no thunderstorm
activity forecast the radar was switched OFF. The aircraft had been in clear skies above towering Cu
for most of the flight and, in accordance with normal procedures, the radar had only been turned on
when required.
As the flight progressed the aircraft entered some high Cirrus cloud. The FO, anticipating the
possibility of turbulence, switched on the 'seat belt' signs and made a short public address (PA)
informing the passengers and cabin crew that this was a precautionary measure. Shortly after the
announcement the aircraft entered what the crew described as an area of 'light innocuous turbulence'.
Approximately 20 seconds later however, the turbulence increased through moderate to become
severe. The autopilot (AP), which was selected ON in the 'Navigation Mode' at a speed of Mach 0.78
(M0.78), disconnected and the aircraft climbed rapidly above its assigned level. Intense hail then
began to impact the aircraft. Both flight crew noted the master warning light illuminate as the
autopilot disconnected but neither pilot heard the associated audio warning due to the noise of the
hail. The FO flew the aircraft manually, selected engine ignition ON, set the speed to M.076 for the
turbulence and turned on the cockpit dome light. The commander changed the range selector on
Navigation Display (ND) to 40 nm to check for conflicting traffic on the Traffic Collision Avoidance
System (TCAS), monitored the aircraft's speed on his Primary Flight Display (PFD), monitored the
first officer's side stick inputs and cancelled the master caution light. Throughout, the PF attempted to
regain FL340 and maintain track. The aircraft however, deviated 1,300 feet above to 300 feet below
its assigned cruising level, rolling to angles of bank not exceeding 18°. Indications on the Vertical
Speed Indicator (VSI) confirmed that on at least one occasion the rates of climb or descent exceeded
5,900 feet per minute.
A Boeing 757 was approximately 25 nm behind G-MIDJ on the same track. The commander of the
757 had his radar selected ON and he could not only see the weather radar returns on his ND but also
G-MIDJ displayed by his TCAS. He thought that G-MIDJ had been heading for the gap between two
lines of thunderstorms displayed on his radar but realised the gap was closing as the storms were
building. He continued using his radar and noted the rapid increase in altitude of G-MIDJ on TCAS
as it entered the storm. Initially, in the absence of any radio traffic he initially assumed that G-MIDJ
Airbus A321-231, G-MIDJ
4
was attempting to climb over the storm. He requested a turn to the right to avoid the weather, which
was approved and passed safely clear of the storm activity.
Moments later the commander of G-MIDJ transmitted to Budapest ATC informing them that they
were unable to maintain FL340 due to severe turbulence. He was unable to hear the reply because of
the hail. This also prevented the pilots from hearing each other for, although they were wearing
headsets, it is normal practice for the intercom to be selected OFF and cross-cockpit conversation to be
conducted without the use of intercom.
After the aircraft cleared the area of turbulence and hail associated with the storm cell the pilots
noticed that the left front (commander's) windscreen and the right (first officer's) Direct Vision (DV)
window had sustained severe hail damage. The commander felt his windscreen and noted that,
although there were visible signs of damage to the outer layers and an increase in airflow noise, the
inside layer was undamaged but the heating had failed. The only caption displayed on the Electronic
Central Aircraft Monitoring (ECAM) system indicated that the aircraft's ILS status had been
downgraded to Category (CAT) III single only. The commander therefore referred to the Quick
Reference Handbook (QRH) for the procedure to deal with a 'cracked windshield'. This required a
descent to FL230 or below and a maximum cabin differential pressure of 5 psi. Budapest ATC
instructed the crew to contact Austrian Radar for their descent clearance and although only 'even'
levels (FL240, FL220) are normally available for westbound flights on this route, the aircraft was
cleared to the requested level of FL230. The aircraft descended gently at 1,500 feet per minute and, in
accordance with the QRH procedure, the pressurisation was controlled manually. During the descent
the Cabin Service Director (CSD) reported to the commander that everyone in the cabin was secure
and that there were no injuries. The commander explained that the situation was still being assessed
and an appropriate course of action considered.
The flight crew interrogated the system pages of the ECAM and noted that the engines appeared
undamaged as individual engine vibration levels had not been affected as a result of the incident. The
aircraft's fuel state had been checked approximately 20 minutes prior to the incident and at that time
there had been an excess of 900 kg over the flight requirements. The aircraft appeared to have
suffered only windscreen damage and the crew confirmed that at the lower cruising level of FL230
there was still sufficient fuel available to complete the flight. With sufficient fuel and no indication of
the aircraft being unsafe the crew elected to continue to Manchester and informed ATC that they had
damaged windscreens and would maintain FL230. Frequent monitoring of the fuel available against
that required by the flight plan and the Flight Management Guidance System (FMGS) confirmed that
sufficient fuel was available to land at Manchester with more than the minimum fuel required.
When the crew contacted London ATCC they re-confirmed that the aircraft had damaged
windscreens. They were radar vectored for a CAT I ILS approach to Runway 24R at Manchester
where the PF was able to carry out a normal manual landing, having disconnected the AP at
approximately 800 feet on finals. The commander was able to monitor the approach even though his
windscreen was significantly crazed. The FO taxied the aircraft to the stand where, as was normal
procedure for that stand, the commander was able to park the aircraft under the guidance of a
marshaller. The passengers exited the aircraft normally using steps positioned at doors L2 and L4.
It was not until the crew vacated the aircraft that they were aware of the extent and severity of the
damage to other areas of the airframe. Even though the manufacturer later confirmed that the aircraft
was in a safe condition to continue to its destination the commander stated that had he known the full
extent of the damage he would have diverted after the incident to the nearest suitable airfield.
Airbus A321-231, G-MIDJ
5
Meteorology
The synoptic situation at 1500 hrs on 26 May 2003 showed a frontal system lying from Poland to
Switzerland with a potentially very unstable airmass to the east of the frontal boundary. Isolated
Cumulo-nimbus clouds, with tops up to approximately FL400, were over the area around eastern
Austria, Hungary, Czech Republic and Slovakia with associated hail, icing and turbulence. A ridge of
high pressure was situated over the southern half of the British Isles with a weak warm front
approaching England and Wales from the west.
The original written weather forecast, obtained by the crew prior to the flight, was not required to be
retained after landing and was not available for scrutiny. A copy of the relevant Significant Weather
chart, obtained from the Meteorological Office, however, is shown at Figure 1. This indicates isolated
(ISOL) embedded (EMBD) Cb cloud with tops up to approximately FL300 over the Alps. It should
be noted that the International Civil Aviation Organisation (ICAO) standard specifies that only
EMBD Cb and occasional (OCNL) Cb or more, but not isolated ISOL Cb, should be depicted on the
chart.
Figure 1: Significant Weather Chart
Airbus A321-231, G-MIDJ
6
Satellite information
Airbus A321-231, G-MIDJ
7
Satellite images of the cold front showing the weather and Cb activity are shown at Figure 2 with the
approximate aircraft track indicated.
Figure 2: Satellite images
Airbus A321-231, G-MIDJ
8
The radar picture
The actual weather radar picture seen by the crew is not recorded and therefore cannot be reproduced.
A representative drawing from the crew of G-MIDJ, illustrating the radar returns they remembered
seeing on their display some time before the incident, is shown on the left below. (Note: the crew
reported that they thought the tilt was set between 2º and 3º down at this time).
Figure 3: Representative drawing from the crew of G-MIDJ
The commander of the 757, who had his weather radar and TCAS selected ON and was using the tilt
function of the scanner, saw on his display the TCAS return from the aircraft ahead and the weather
radar returns. He was able to recollect the display at the time and an illustration of that display is
shown on the right above.
Flight Recorders
The Digital Flight Data Recorder (DFDR) and Cockpit Voice Recorder (CVR) were removed from
the aircraft and replayed at the AAIB.
Cockpit voice recorder
The CVR (2 hour duration) contained only a 30 minute recording of the incident flight as electrical
ground power continued to be supplied to the unit after landing, over-writing some of the pertinent
recording. The CVR however, confirmed that the first officer was the PF and that the hail damage
had rendered the commander's windscreen crazed. The only other matter of note on the recording was
an increase in cockpit ambient noise level after the hail encounter.
Digital flight data recorder
The DFDR contained a time history of the entire flight and showed that the aircraft took off at
1300 hrs and climbed steadily towards its cruising altitude. Two hours and twelve minutes into the
cruise the DFDR recorded a severe turbulence encounter (see Figure 3) that lasted in excess of
3 minutes causing disturbances in all aircraft axes. The most severe disturbances were in the 'pitch'
and in the 'normal' axes. Recordings during the encounter showed a maximum nose down pitch
attitude of -15o and a normal acceleration ranging between +1.5 g and -0.3 g. The aircraft descended
to FL230 six minutes after the encounter and remained at this flight level until its descent into
Manchester. The aircraft landed normally, with the first officer at the controls, at 1803 hrs.
Airbus A321-231, G-MIDJ
9
Figure 4: DFDR Trace for G-MIDJ
Airbus A321-231, G-MIDJ
10
Airbus A321-231, G-MIDJ
11
Weather radar data
Recorded data concerning the use of the weather radar (see Figure 4) showed that it was switched on
and displayed to the first officer for approximately 12 minutes as the aircraft climbed from 4,700 feet
through 23,600 feet. The DFDR did not record any use of the weather radar during the remainder of
the flight.
Figure 5: DFDR Trace for G-MIDJ
Airbus A321-231, G-MIDJ
12
Airbus A321-231, G-MIDJ
13
After the aircraft had been repaired AAIB inspectors, with the assistance of the operator's engineers,
carried out a full operational check of the weather radar and its recording on the DFDR. The DFDR
data was downloaded after the check and analysis confirmed that the DFDR faithfully recorded the
use of the weather radar. It should be noted however that the data recording was not confirmed post
incident before major repair work had been undertaken and some radar components had
been replaced.
Passenger cabin activity`
In the aircraft cabin, which was in a 'Charter' configuration, were 213 passengers and 6 cabin crew,
including a Cabin Service Director (CSD), working with two crew in the forward cabin and three in
the aft cabin area. Although the outbound flight had been uneventful the aircraft commander had
warned the cabin crew, at their initial briefing, that they could experience some turbulence during the
outbound sector of the flight.
The incident
Immediately prior to the incident, the cabin crew were positioned with three in the forward galley,
two in the aft galley and one who had just commenced moving forward through the cabin. The meal
service had been completed and all the passenger food trolleys had been stowed and secured. All
were aware that the seat belt sign had been switched ON and heard the PF's PA announcement
warning of possible turbulence. The PF contacted the CSD on the interphone after making the PA
announcement to confirm it had been heard and was being responded to.
Several passengers and cabin crew members were not seated and secure when the turbulence rapidly
increased from slight, through moderate to severe causing the aircraft to enter a sudden and rapid
descent. The cabin crew member and three passengers moving forward along the aisle to return to
their seats fell to the floor and remained there. One passenger, seated but not secure, rose out of her
seat and struck her head on the overhead Passenger Service Unit (PSU). A cabin crew member,
unsuccessfully attempting to stow the crew meals trolley in the rear galley, was lifted from the floor,
along with the trolley. A cabin crew colleague, seated and secure in an adjacent cabin crew seat,
however, attempted to hold onto her to prevent her from falling. Two cabin crew members, along
with the CSD, positioned in the forward galley, had not had time to make themselves secure. They
also rose clear of the floor momentarily. The CSD was able to make a short PA for everyone standing
to sit down on the floor. Those passengers who ended up on the floor were restrained, as much as was
possible, by the crew.
Post incident
When the noise had abated and the turbulence ceased those passengers and crew on the floor got up
and the passengers returned to their seats. The CSD contacted the flight deck on the interphone and
was instructed by the commander to keep the passengers seated. He also reassured him that the flight
crew were in full control of the aircraft and would call back shortly. The CSD used the PA to check if
any of the passengers were injured but none were. He then walked to the rear galley to ensure that
none of the rear cabin crew was injured. As passengers remained in their seats, two passengers, who
had been occupying the front and rear toilets at the time of the incident, emerged shaken but uninjured
to return to their seats. The cabin crew cleared up the galley areas and a senior stewardess moved
through the cabin talking to each passenger and reassuring those that were distressed. The CSD
visited the flight deck to inform the commander that the passenger cabin was safe and that no one had
been injured. He was briefed by the commander that the windscreen was damaged but all other
aircraft systems were normal and, subject to fuel considerations, the aircraft would continue on to
Manchester. This information was relayed to the other cabin crew members. Once order had been
restored the commander authorised the commencement of a bar service to enhance an atmosphere of
normality and approximately one hour later, at the request of the senior stewardess who had spoken to
the passengers, a further PA was made to reassure the passengers.
Airbus A321-231, G-MIDJ
14
Aircraft damage
The aircraft sustained damage to most of the leading edge surfaces of the airframe. The outer layer of
the radome surface had been damaged by the hail although it was not punctured. Airflow impinging
on the damaged outer layer then caused the inner honeycomb layer to implode onto the flat plate
antenna of the weather radar, rendering it unusable. Post incident inspection of the radome, by the
aircraft manufacturer, showed that it was not at risk of detaching from the aircraft.
The captain's windscreen suffered a cracked outer layer, as had the FO's DV window. The damage to
the captain's windscreen was to the extent that the windscreen heater element, which ran through the
outer layer, was rendered inoperative. The first officer's main (front) windscreen remained intact.
Both were subsequently subjected to a detailed examination by the manufacturer. The windscreen
and DV window, which are constructed of several plys, consist of an outer ply of glass that is nonstructural,
and internal plys, also of glass, providing the structural element. Both the cracked
windscreen and DV window showed evidence of several impact damage points from the hail,
resulting in the fracture of the glass. This was limited to the outer ply and did not cause a reduction in
the structural integrity of either of them. Inspection of the captain's main (front) windscreen showed a
single fracture origin in the lower third of the glass and in excess of 85 other impact points. The first
officer's DV window showed two fracture origins in the glass and approximately 8 additional impact
points.
Other areas of the aircraft structure also sustained extensive damage from the hail. The crown skin
above the flight deck suffered several dents some to a depth of approximately 0.05 inches with a
diameter of 1 inch. There was also denting to the aircraft skin below the first officer's DV window.
The leading edges of the wings, the engine intake lips, the engine saddle fairings and the horizontal
stabiliser all had dents along their leading edges. The horizontal stabiliser tips exhibited the worst
damage, with the left tip being holed.
The composite structure of the aircraft, the wing to body fairings, pylon to wing attachment fairings
and the leading edge of the vertical fin, were also exposed to hail damage. This damage, however,
resulted only in paint erosion.
Engine damage was limited to the engine intake lips. The fan blades were intact and showed no signs
of impact with the hail. Furthermore, internal boroscope examination did not show any other damage
within the engines.
The Airbus A321 has a system that produces a post flight report on defects recorded by the computer
systems during flight. Faults were recorded for the captain's windscreen heater, the standby pitot
probe heater and due to autopilot disengagement. All these faults were recorded at 1543 hrs and are
directly related to the hail encounter.
Airbus A321-231, G-MIDJ
15
Weather radar system
The weather radar system fitted to the aircraft works on the principle of radio echoing. The radar
operates in the x-band producing energy at very high frequency in the form of electromagnetic pulses.
These pulses are emitted from a flat plate antenna mounted in the radome at the front of the aircraft.
The antenna scans left to right over an angle of 180° with the pulses being emitted at regular intervals
during the scan. When the electromagnetic pulses come in contact with weather they are reflected
back to the scanner. The direction, distance and intensity is then calculated by a transceiver/receiver
unit and displayed to the crew.
A control panel for the weather radar is provided on the cockpit centre console. This incorporates the
ON/OFF selector of the entire weather radar system. In addition there are controls for gain, tilt, mode
and ground clutter suppression. When the weather radar is switched ON the weather information can
be displayed on the captain's and first officer's ND. Each pilot has a separate control panel on the
glareshield where he can not only control his respective ND but also the range of the weather display
up to a maximum distance of 320 nm. Weather is not displayed if the ND selection is to the 'plan'
mode. An additional system allows for the display of terrain data on the ND rather than weather.
Normal practise is for the PNF to have his ND selected to display terrain data and the PF to have his
ND selected to show weather.
The tilt of the weather radar antenna beam, stabilised automatically in pitch and roll to compensate for
the aircraft's attitude, can be controlled manually to point above and below the horizon up to ±15°.
This allows the antenna beam to be moved upwards to reduce the radar returns from the ground or to
scan different levels of the atmosphere ahead. If the tilt is selected to too high or too low an angle
however, some weather activity, that might affect the aircraft on the track ahead, may be missed.
Weather radar system tests
Following the accident the weather radar transmitter/receiver, control panel and the scanner pedestal
were tested by the manufacturer. During the test of the transmitter/receiver there was a single test
failure on the input/output card, however, despite subsequent repeated tests the fault could not be
reproduced and it was thus concluded that the single failure was a 'test glitch'. The remaining
equipment operated without fault.
Operation and limitations of the weather radar equipment
The operating procedures and limitations of the weather radar are comprehensively covered in the
company's Operations Manual (OM). The Supplementary Techniques in the OM, for the operation of
the weather radar, have been reproduced from the manufacturer's instructions.
The capabilities and limitations of the equipment, detailed in the beginning of the instructions, are
summarised below:
GENERAL
The radar is nothing more than a precipitation detector. How much weather it detects
depends upon the raindrops, their size, composition and number.
The radar does not detect:
Clouds, fog or wind (too small droplets or no precipitation at all)
Clear air turbulence (no precipitation)
Wind shear (no precipitation except in microburst)
Lightning.
Airbus A321-231, G-MIDJ
16
The radar does detect:
Rainfall
Wet hail and wet turbulence
Ice crystals, dry hail and dry snow (above 30,000 feet) will only give small reflections.
The technique for operating the weather radar effectively utilises a combination of range and beam
depression or elevation referred to as tilt. Guidance on the range setting that should be set on the ND
for each pilot for avoiding thunderstorms recommends that the PF selects his ND to 80 nm and the
PNF to 160 nm. The ND should be set to a range of 40 nm when in 'Turbulence Mode' and the
antenna tilted to avoid ground returns. The importance of readjusting the tilt frequently in order to
monitor storm development and to get the best cell echo is emphasised. Failure to tilt the antenna
down periodically may cause a target to disappear.
As the 0° tilt angle is slaved to the horizon, a formula is provided for calculating the vertical distance
between the top of the weather cell and the aircraft flight level. The tilt angle element of the formula
is based on adjusting the tilt until the echo begins to disappear and then noting the tilt angle.
The company provide operating procedures, titled 'Encountering Adverse and Potentially Hazardous
Atmospheric Conditions' covering the situation where thunderstorm activity is detected either visually
or by using the weather radar. The information includes 'Techniques for Flying Through Areas of
Thunderstorm Activity' and the advice given is that above 30,000 feet, 'avoid all echoes by 20 miles'.
Advice also states that 'the pilot should not attempt to penetrate a cell or clear its top by less than
5,000 feet vertically, because otherwise the aircraft may encounter severe turbulence. If the top of the
cell is at or above 25,000 feet, overflying should be avoided due to the possibility of encountering
turbulence stronger than expected'.
A formula for calculating the vertical distance between the top of the weather cell detected on the
radar and the aircraft flight level is provided as:
Vertical distance (feet) = range of cell (nm) x radar depression angle (°) x 100.
Weather radar training
Crew training in the use of the weather radar is carried out during the aircraft type conversion course
and initial line training. Procedures, set out in the 'supplementary techniques' for the use of the
weather radar mentioned previously, and training videos, covering the use of the weather radar and
adverse weather operations, are also provided by the operator.
Airbus A321-231, G-MIDJ
17
Recent developments
The latest weather radar equipment, called a 'multi-scan system', incorporates an antenna that not only
automatically scans left to right but also up and down. This system also incorporates automatic
ground clutter suppression allowing only weather to be displayed. By scanning the whole atmosphere
precipitation at the bottom of the thunderstorm cell, that is normally hidden within ground clutter, can
be detected. Thus thunderstorms can be displayed more clearly and sooner. The present in-service
systems' detection level is poorer in that when set to scan only the top of a thunderstorm cell they will
only be targeting levels of the atmosphere where only dry ice is present. This newer equipment thus
encourages aircraft track adjustments around thunderstorm cells that may contain areas of severe
turbulence present at levels undetected by the present radar equipment.
Flight Management Guidance System (FMGS)
Having checked that the aircraft systems were in a safe condition, the crew used the FMGS to
determine whether the aircraft had sufficient fuel remaining to continue the flight to Manchester.
They decided that an en-route diversion was not required and by remaining on their planned route the
fuel required on the flight plan at each way-point could easily be checked against the fuel available.
The FMGS 'fuel page' provided a calculation of the fuel required to continue to Manchester, at the
lower level of FL230, as well as any extra fuel that was available. The extra fuel available just before
the aircraft entered the hail had been 900 kg. The fuel calculations made by the FMGS, however, are
based on aircraft performance data stored in the computer. This data (also available to the crew in
hard copy), calculated on the assumption that the aircraft is aerodynamically undamaged, and not on
fuel actually being consumed, is used to establish the fuel required. The extra fuel figure is
continually re-calculated by the FMGS by subtracting the fuel required from the fuel available.
The radome and aerodynamically significant airframe surfaces of G-MIDJ were damaged by hail and
the total drag coefficient of the airframe, and thus its performance were, to some unknown extent,
affected. The FMGS fuel calculations did not take account of this change and thus the fuel required to
destination, displayed to the crew, was somewhat unrepresentative. In the event the resultant increase
in drag was subsequently found to be insignificant and constant monitoring of the fuel state by the
crew ensured that the aircraft arrived at its destination with more than the minimum fuel prescribed.
It is interesting to note that, according to the manufacturer, if the radome had become detached from
the aircraft, the fuel burn, resulting from the increased drag, could have been increased by as much as
27%. This would clearly have caused a major difference between the computed fuel required and the
actual fuel required and would have manifested itself as a rapid reduction in the extra fuel available or
the estimated fuel at destination.
Airbus A321-231, G-MIDJ
18
Discussion
Thunderstorm activity was only depicted on the forecast Significant Weather charts for the route to
Cyprus as 'ISOL EMBD CB' over the Alps. This was noted by the flight crew and at the pre-flight
briefing the commander warned the cabin crew of the possibility of turbulence occurring during that
part of the flight. The line of CB activity associated with the cold front lying across Hungary was not
depicted on the chart as its intensity was forecast as not meeting the 'EMBD' or 'OCNL CB' criteria.
The departure from Cyprus was flown in clear conditions where the weather radar was only used to
monitor the cloud building up over the northern part of the island and over the Turkish mainland to
the right of the intended track. This weather was clearly depicted on the chart and the commander
visually assessed the tops of the clouds to be at approximately FL280. Thereafter the flight was
generally conducted in clear conditions above some ISOL CU with the flight crew being able to
visually assess the weather ahead of the aircraft. The weather radar, when selected, was displayed on
the ND being used by the PF and was visible to the commander.
As the flight progressed neither pilot adjusted the radar tilt leaving it selected 2º to 3º down. They
were satisfied that the weather returns to the right and minor returns to the left of track posed no
significant threat to the aircraft and thus the radar was selected OFF.
The weather radar has the limitation that ice crystals, dry hail and dry snow above 30,000 feet will
only give small reflections. A pilot must therefore rely on vertical scanning of a storm cell, using the
tilt facility to direct the radar beam, in order to detect adverse weather. This was not the technique
being used when the crew observed what they interpreted as minor returns before they deselected the
radar. They thus entered an area of significant turbulence and hail without warning.
As a result the aircraft suffered significant damage to the airframe and some of the flight deck
windows. The only damage visible to the crew however was that evident on the flight deck. Neither
the commander nor the FO left the flight deck to examine the wings or engine intakes from the
passenger cabin windows. Had they done so it is unlikely that they would have been able to
appreciate the level of damage to the aircraft as the small but numerous indentations left by the hail
stones were not visible from the cabin. Furthermore, the areas where the hail had penetrated the
aircraft skin were not visible from within the aircraft.
The manufacturer's opinion was sought regarding whether or not a diversion should have been carried
out given the level of damage caused to the aircraft. They believed that the design of the structure,
based on certification requirements and design specifications, was such that it absorbed the damage
and the aircraft remained in a safe condition.
The FMGS provided information on the fuel estimated to be on board when the aircraft arrived at its'
destination and any extra fuel available. When the aircraft descended and levelled at FL230 these
amounts were recalculated by the FMGS computer and should have remained constant for the
remainder of the flight. Any unexplained reduction of these amounts could have indicated
degradation in the aircraft's performance brought about by an increase in airframe drag caused by the
damage. This would have been of greater potential significance if the aircraft had been carrying out
an Extended Range Twinjet Operation (ETOPs).
The windscreen in front of the commander and the DV window on the FO's side were both damaged.
In the event, although the first officer carried out the landing and taxi to the stand, the commander still
had enough vision to park the aircraft. It is worthy of note that if the damage had been more
significant and the visibility through both front windscreens had been degraded the crew would still
have been able to have landed the aircraft using the autoland facility.
Finally, testing of the FDR showed that it correctly recorded when the weather radar was selected ON
or OFF. This recorded evidence however, is at variance with the recollection by the crew of when the
radar was being operated. It is of note that the FDR discreet, recording the status of the weather radar,
was only tested after significant disruption to, and reconnection of the aircraft avionics system.
Airbus A321-231, G-MIDJ
19
Therefore because the reliability of the recorded evidence could be questioned the investigation
accepted the account of the events provided by the crew.
Airbus A321-231, G-MIDJ
20
Conclusions
This serious incident occurred when the aircraft, initially cruising in VMC, entered an area of cirrus
cloud and penetrated an area of severe turbulence and hail. The weather radar, when used by the
crew, did not show the severity of the weather ahead of the aircraft. This weather however, was
observed by the crew of the B757 on their weather radar display. The apparent lack of significant
weather returns resulted in the crew of the G-MIGJ turning off their weather radar. Having entered
the area of turbulence and hail associated with a storm cell, the PF made measured control inputs,
monitored by the commander, which reduced the excursions of the aircraft without imposing large
load factors on the airframe or those onboard. The absence of injuries sustained by the passengers
and crew was solely attributable to the timely illumination of the fasten seat belt signs and the fact
that most passengers were seated with their seat belts secure. The actions by the cabin crew, in not
attempting to move about the cabin but remaining on the floor during the worst of the turbulence,
probably assisted in avoiding injury. The maintenance of communication between the flight deck and
cabin crew throughout the flight meant that all crew were fully aware of the resulting course of action
decided upon by the commander. Having made an assessment of the damage to the aircraft caused by
the hail and the serviceability of the aircraft systems the flight deck crew continued to the planned
destination of Manchester, monitoring the fuel situation to ensure adequate fuel was available to
safely complete the flight.
It was not until the crew vacated the aircraft that they were aware of the extent and severity of the
damage to other areas of the airframe. Even though the manufacturer later confirmed that the aircraft
was in a safe condition to continue to its destination the commander stated that had he known the full
extent of the damage he would have diverted after the incident to the nearest suitable airfield.
Follow-up actions
The operator has since issued a Flying Staff Instruction to all flight crews reminding them of the
correct use of the weather radar.
Airbus A321-231, G-MIDJ
21
Recommendation
Present guidance material not only suggests that, in areas of thunderstorm activity, readjusting the
radar tilt frequently is the only way to monitor storm development but also that when the upper limit
of the storm cell is determined it should be avoided vertically by at least 5,000 feet. The inability of
weather radar to detect certain types of precipitation, associated with storm cells, in the upper levels of
the atmosphere above 30,000 feet however make it impossible to determine with any accuracy the
upper limit of a cell when its vertical development exceeds 30,000 feet. Calculations to determine the
aircraft's clearance above the upper limit of a cell can therefore be inaccurate resulting in an aircraft
entering the active element of a storm cell whilst attempting to safety over-fly it. It is therefore
recommended that:
Safety Recommendation 2004-47
The Civil Aviation Authority should consider reviewing their guidance material concerning the use
and interpretation of airborne weather radar, with a view to highlighting the potential for displayed
data to be unreliable when used for calculating the safe vertical clearance for overflight of active
storm cells.

f214216709

看看的 谢谢楼主

kmlihe

thank you very much