Boeing Quiet Climb

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航空

26 AERO First-Quarter 2003—January
Boeing has developed the Quiet Climb System, an automated avionics feature
for quiet procedures that involve thrust cutback after takeoff. By reducing
and restoring thrust automatically, the system lessens crew workload and
results in a consistently quiet footprint, which helps airlines comply with
restrictions and may allow for an increase in takeoff payload.
Quiet Climb
First-Quarter 2003—January AERO 27
JERRY FRIEDRICH
AVIONICS DESIGN ENGINEER
NAVIGATION/GUIDANCE/THRUST MANAGEMENT
BOEING COMMERCIAL AIRPLANES
DANIEL MCGREGOR
AIRPORT AND COMMUNITY NOISE ENGINEER
COMMUNITY NOISE
BOEING COMMERCIAL AIRPLANES
DOUGLAS WEIGOLD
AERODYNAMIC PERFORMANCE ENGINEER
AIRPLANE PERFORMANCE & PROPULSION
BOEING COMMERCIAL AIRPLANES
ADVANCED
AVIONICS
FOR
QUIET
OPERATIONS
T E C H N O L O G Y / P R O D U C T D E V E L O P M E N T
System
28 AERO First-Quarter 2003—January
ith higher density populations
surrounding airports
throughout the world,
the sound of airplanes has become
an issue of increasing importance in
recent years. Noise-abatement requirements
and procedures imposed by
local airport authorities have affected
airline operations in many ways,
resulting in restricted hours of
operation, required weight offloads,
fines, and surcharges.
Airplane and engine manufacturers
have been successful in producing
quieter airplanes, but more stringent
noise-abatement requirements and
the high cost of engine modification
have prompted the industry to consider
additional ways to decrease
airplane sound in communities.
One alternative is a maneuver in
which the flight crew takes off with
full takeoff power, climbs rapidly,
and then cuts the thrust manually to
a predetermined value at a specified
cutback altitude. The airplane continues
to climb, albeit at a much
slower rate, until it is high enough
that sound in the community is not
an issue. The crew then adds more
power to continue flight.
One potential problem with this
maneuver is that the pilot must cut
back and restore engine thrust manually
at the correct altitudes. The Boeing
Quiet Climb System (QCS), which is
selected during the takeoff procedure,
automatically reduces and restores
engine thrust at the specified altitudes,
thereby reducing pilot workload.
In an effort to standardize noiseabatement
procedures, the Federal
Aviation Administration (FAA)
has issued advisory guidelines that
define departure profiles, including
the minimum thrust required and
the cutback altitude. This article
discusses
1. FAA advisory guidelines.
2. The Boeing QCS.
3. Basics of sound measurements.
4. Effect of the Boeing QCS on
sound in communities.
FAA ADVISORY GUIDELINES
In 1993, the FAA issued advisory
circular AC91-53A, “Noise Abatement
Departure Profiles,” which standardizes
procedures by defining acceptable
criteria for speed and minimums for
thrust cutback settings and altitudes for
various airplane takeoff configurations.
Minimum thrust cutback.
The minimum thrust cutback represents
the minimum level of thrust that would
ensure a sufficient climb gradient if an
engine were to fail. This thrust value is
determined by the number of engines
on the airplane. On a two-engine
airplane, the minimum thrust cutback
ensures an engine-inoperative climb
gradient of 1.2 percent. If one engine
fails after cutback, the thrust from the
operating engine must maintain a climb
gradient of at least 1.2 percent. On
three-engine and four-engine airplanes,
the minimum thrust cutbacks are
engine-inoperative climb gradients of
1.5 percent and 1.7 percent, respectively.
Zero percent gradient cutback.
Under certain conditions, the advisory
circular also allows a thrust cutback
that maintains a zero percent engineinoperative
climb gradient. This type
of cutback is permitted for airplanes
with avionics systems that can detect
engine failure and automatically
increase the thrust on the remaining
engine or engines to a value that
maintains the minimum climb gradient.
These minimum climb gradients are
1.2 percent on a two-engine airplane,
1.5 percent on a three-engine airplane,
and 1.7 percent on a four-engine airplane.
Cutback altitude.
The advisory circular also specifies
that the minimum altitude at which the
thrust can be reduced, or cut back, is
800 ft above ground level (AGL).
THE BOEING QCS
Boeing developed the QCS, an
advanced avionics feature, to directly
assist flight crews in flying the quiet
departure profiles defined in the
advisory circular. The QCS controls
thrust reduction and restoration
automatically, thereby eliminating
the need for manual control and
ensuring consistency.
During the takeoff checklist procedure,
the pilot selects the QCS and
enters the altitudes at which thrust
should be reduced (≥800 ft AGL) and
restored. With the autothrottle system
engaged, the QCS reduces engine
thrust when the cutback altitude is
reached to maintain the optimal climb
angle and airspeed. When the airplane
reaches the chosen thrust restoration
altitude (typically 3,000 ft AGL), the
QCS restores full climb thrust automatically.
As such, QCS reduces pilot
workload during a phase of flight that
already is task intensive.
QCS incorporates multiple safety
features and will continue to operate
even with system failures. If a system
failure does occur, there are several
methods for exiting QCS. In the most
common method, the pilot selects
the takeoff/go-around switches on the
throttle control stand. The pilot can take
control of the throttles easily by disconnecting
the autothrottle and controlling
the thrust manually, as appropriate.
QCS availability.
The QCS is available on all 737-600/
-700/-800/-900 airplanes and provides
an automatic thrust cutback
engine-inoperative climb gradient of
1.2 percent. The zero percent climb
gradient QCS is scheduled to become
available in first-quarter 2003 on
the 737-600/-700/-800/-900. Boeing
also is considering the QCS for the
747-400, which would have an
2
1
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First-Quarter 2003—January AERO 29
automatic thrust cutback engineinoperative
climb gradient of 1.7 percent.
Other Boeing systems.
A system similar to the QCS is available
on the MD-90 series. That system,
however, requires that the pilot calculate
the necessary thrust and then enter
it manually for automatic thrust cutback
during takeoff. The 757 also has an
option similar to QCS that provides
an engine-inoperative climb gradient
of 1.2 percent. To be activated, the
crew must select the system manually
at the cutback altitude.
BASICS OF SOUND
MEASUREMENTS
Airplane sound is measured along
the flight path using monitors located
near the ground. The level measured
by each monitor is a function of the
airplane, engine type, altitude, and
thrust. An airplane event consists
of a single flyover with incremental
measurements recorded by the
monitors (fig. 1). A time history,
which is a composite of the individual
measurements, shows changes in
the sound level over time. The history
provides information on the maximum
(peak) level and the duration
of the event.
Three common ways
of representing sound.
One common way to represent airplane
sound uses peak A-weighted decibels
(typically referred to as peak dBA),
which are decibels adjusted for how
the human ear hears sound (fig. 1).
Another way to represent sound is
time-integrated measurement (fig. 2).
With this method, individual measurements
of energy taken over time are
summed.
A third way to represent airplane
sound uses a contour, or footprint. A
footprint shows the impact of sound
on communities near the airport and
provides information about how variables
such as airplane configuration,
flight procedures, and new airplane
technology (e.g., QCS) affect the size
and shape of the footprint (fig. 3).
London Heathrow Airport.
London Heathrow Airport, in the
United Kingdom, is one of the world’s
most heavily regulated airports. It has
four departure runways for commercial
airplanes and 10 sound monitors. To
regulate airplane noise and its impact
on local communities, the airport has
established peak dBA noise limits for
daytime, shoulder period, and nighttime
operations. The daytime (7 a.m. to
11 p.m.) limit is 94 dBA; the shoulder
period (11 p.m. to 11:30 p.m. and
6 a.m. to 7 a.m.) limit is 89 dBA; the
nighttime (11:30 p.m. to 7 a.m.) limit
is 87 dBA. For long-haul carriers with
3
heavy fuel and passenger payloads, the
lower two limits are difficult to meet.
John Wayne Airport.
John Wayne Airport, in Orange
County, California, is another of the
most heavily regulated airports. The
airport has one departure runway for
commercial airplanes and seven monitors.
Airplane sound is measured using
a single-event noise-exposure level
(SENEL), which is a type of timeintegrated
measurement. The SENEL
also uses dBA time history, but rather
than reporting only the peak dBA, the
energy of all sound levels >65 dBA
is added to produce a single value.
Time
Sound level, dBA
Thrust cutback
Peak dBA
Monitor
Incremental
noise measurements
Airplane approaching monitor
Airplane flying over monitor
Airplane leaving monitor
Time
65 dBA
Sound level, dBA
Thrust cutback
Monitor
Sum of total energy
(single-event noise-exposure level)
Airplane approaching monitor
Airplane flying over monitor
Airplane leaving monitor
FLYOVER SOUND IN A-WEIGHTED DECIBELS
FIGURE
1
FLYOVER SOUND IN TIME-INTEGRATED MEASUREMENT
FIGURE
2
First-Quarter 2003—January
75 dBA sound contour levels
QCS with thrust cutback to maintain
engine-inoperative climb gradient of 0%.
Footprint area reduced by 21%.
QCS with thrust cutback to
maintain engine-inoperative
climb gradient of 1.2%.
Footprint area reduced by 14%.
Without QCS.
Thrust cutback to
maximum climb power.
Baseline footprint.
-5,000 ft Source: The Boeing Company
4,400 ft 5,000 ft
10,000 ft
15,000 ft
Distance from brake release
20,000 ft
25,000 ft
0 ft
30 AERO
EFFECT OF THE BOEING QCS
ON SOUND IN COMMUNITIES
The QCS reduces takeoff sound by
reducing thrust, which helps airlines
comply with noise restrictions that carry
increasingly severe economic penalties
for violations. At John Wayne Airport,
for instance, fines can be as much as
$500,000. To avoid such penalties, airlines
that use a manual procedure to cut
back and restore thrust during takeoff
often reduce takeoff weight to ensure
that sound levels stay within designated
limits. Because the QCS standardizes
the noise-abatement maneuver, the
system minimizes the need to reduce
takeoff weight. This, in turn, provides
airlines with the added economic
benefit of allowing airplanes to carry
more passengers, cargo, or fuel.
The Quiet 737-800.
On current-production 737-800s with
CFM International CFM56-7B26
engines, the QCS reduces the acoustic
footprint by 14 percent. On these
airplanes, the zero percent climb gradient
QCS is expected to reduce the
acoustic footprint by 21 percent. At
John Wayne Airport monitor three (the
most critical monitor for the 737-800),
a typical departure with the 1.2 percent
climb gradient QCS would lower the
SENEL by ~3.2 dB. This improvement
would permit an ~5,500-lb increase
in payload with the same sound level
registered at takeoff as on similar
airplanes without QCS. The zero percent
climb gradient QCS would lower
the SENEL by an additional 1 dB at
the same payload.
A Quieter 747-400.
Approximately 90 percent of the
747-400s operating out of London
Heathrow Airport could be quieter by
slightly more than 1 dBA if they were
equipped with the 1.7 percent QCS.
The reduction would be even more
significant for airplanes with lower
takeoff weights. Alternatively, with the
QCS, 75 percent of the 747-400s departing
from Heathrow could increase
their takeoff weight by an additional
25,000 lb and be as quiet at the monitors
as similar airplanes without QCS.
4
THE BOEING QCS
FIGURE
3
First-Quarter 2003—January AERO 31
SUMMARY
In response to increasingly stringent
noise regulations and customer need,
Boeing has developed the QCS, an
advanced avionics systems feature
that reduces pilot workload during the
labor-intensive period of takeoff while
helping airlines meet requirements
without incurring penalties. The QCS
automatically moves the throttle
controls and retards engine thrust to
maintain an optimal climb angle and
airspeed, thereby reducing sound in
the community and minimizing the
impact on communities near an airport.
An airplane equipped with the
QCS may be able to carry more cargo,
fuel, or passengers and still be quiet.
The QCS currently is available on
737-600/-700/-800/-900 airplanes
and is being considered for use on
747-400s. Some other Boeing models
have systems similar to QCS.
Jerry Friedrich
has been with Boeing for
15 years and is an avionics
design engineer and a
Designated Engineering
Representative in the thrust
management/autothrottle
group that supports 737, 757,
767, and 777 airframes.
Daniel McGregor
has been with Boeing since
1985 and has extensive experience
developing prediction applications
that support airplane certification,
community noise research, and
interior noise. He is a lead engineer
in Noise and Emissions and
develops operational procedures
to reduce the impact of airplanes
in communities. He also is leader
of the Boeing John Wayne Airport
Air Carrier support team, which
has streamlined airport review
and qualification requirements
resulting in cost savings for
airlines and John Wayne Airport.
Douglas Weigold
is a 14-year veteran of the
aerospace industry and has
worked on airplane programs
that include Longer Range
777, 717, MD-11, and High
Speed Civil Transport. As part
of the Production and Fleet
Support Aerodynamics group,
he currently works on narrowbody
performance issues and
is group noise focal for all
airplane models.
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