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members, cargo, and the airplane. Therefore, any procedure introduced to taxi or idle an aircraft
with less than the full complement of engines is at the discretion of the pilot. If back blast
endangers persons or property, it is a violation of the FAR for which the pilot would be subject to
FAA disciplinary action.
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6.1.2 Derate Takeoff Power
Aircraft are designed to have adequate power to takeoff under extreme conditions such as very
hot days when they are fully loaded with passengers, cargo, and fuel. When the conditions do not
require full power, a derated takeoff procedure can be used to limit the engine thrust to the
minimum necessary. By operating the engines at a lower power setting, the NOx emissions can be
reduced.
From a safety standpoint, a derated takeoff is feasible for most aircraft. Reduced power takeoffs
currently are being used by most air carriers to enhance engine life and to increase fuel
conservation and engine reliability time. A number of large airlines currently rely on the Central
Air Data Computer’s (CADC’s) computations to determine takeoff throttle settings. This
computed value depends on various aircraft, runway, meteorological, and regulatory variables.
This computed throttle setting is often in the range 0.75 to 0.90, but still well below 1.0 (or
100%). The lower throttle setting limit is often established by the FAA regulatory requirements
to ensure an aircraft’s minimal climb out angle maintains a safety margin that accounts for
engine failure. Thus, takeoff throttle settings almost always exceed climb out values independent
of the length of the runway. Certain FAA procedures are already in place to deal with derated
takeoffs. FAA Advisory Circular (AC) No. 25-13, Reduced and Derated Takeoff Thrust (Power)
Procedures, describes the requirements when using reduced power for takeoff. AC No. 91-53a,
Noise Abatement Departure Profiles, is applicable to operators of large turbojet airplanes.
Within the provisions of this AC, each airport can define the departure procedures that best
serves their community from a noise impact perspective.
Site-specific factors such as wind, weather conditions, aircraft type, and aircraft weight are
critical considerations to plan for when performing a derated takeoff. They influence a pilot’s
decision as to when a derated takeoff may be safely implemented. In addition, noise abatement
procedures and length of the runway at some airports require full power for all takeoffs. If
derated takeoff is used, it should remain within the discretion of the pilot in command.
6.1.3 Reduce Use of Reverse Thrust
After aircraft land, they often rely on engine thrust reversal to slow the aircraft to taxi speed.
Reverse thrust normally is used to reduce the time on the active runway after landing and to
reduce maintenance costs incurred with brake repair and replacement. On long runways, it is
possible to eliminate reverse thrust and slow the aircraft using only the wheel brakes. Reverse
thrust is a high power operation for engines and a source of NOx emissions. Eliminating the use
of reverse thrust reduces NOx emissions. In some cases, this may occur at the expense of slightly
higher HC emissions if taxi time is increased because a runway turnoff is missed or more time is
needed for the landing aircraft to exit the runway. If the time needed for the landing aircraft to
exit the runway is increased, it also may increase the taxi/idle time (and emissions) of aircraft
awaiting takeoff and landing.
Use of reverse thrust is a matter of safety. It is used at the discretion of the pilot in command of
the aircraft. Many factors are involved in the decision to use reverse thrust including runway
length and width, runway surface conditions, weather conditions, aircraft type, the pilot’s desire
for a smooth landing, location of intersections for turning off of the runway, taxi way condition
and congestion (i.e., other traffic), and proximity of aircraft following on final approach.
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6.2 Auxiliary Power Units
Emissions from APUs can be reduced by turning off the APU while an aircraft is docked at the
gate. Turning off the APU reduces fuel combustion. When available at the gate, a 400 Hz ground
power system and ventilation air source often provide a reasonable alternative to using an APU
to support normal aircraft operations. These fixed systems operate at a greater energy efficiency
than an APU and substantially reduce pollutant emissions. In addition, the emissions attributable
to the generation of electricity for use by the fixed systems usually are generated at an off-airport
electric power plant. The emissions generated at the power plant are lower due to higher
efficiency and emission controls. Often the cost of the fuel saved is greater than the cost of
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Air Quality Handbook航空质量手册(34)
