Federal Aviation Regulation (FAR) Takeoff Field Length
The FAR takeoff field length is the longest of the following:
.
the distance required to accelerate with all engines, experience an engine
failure 1 second prior to V1, continue the takeoff and reach a point 35 feet
above the runway at V2 speed. (Accelerate-Go Distance).
.
the distance required to accelerate with all engines, experience an event 1
second prior to V1, recognize the event, initiate the stopping maneuver
and stop within the confines of the runway (Accelerate-Stop Distance).
.
1.15 times the all engine takeoff distance required to reach a point 35 feet
above the runway.
Stopping distance includes the distance traveled while initiating the stop and is based on the measured stopping capability as demonstrated during certification flight test.
During certification maximum manual braking and speedbrakes are used. Thrust reversers are not used. Although reverse thrust and autobrakes are not used in determining the FAR accelerate-stop distance, thrust reversers and RTO autobrakes should be used during any operational rejected takeoff.
Calculating a V1 speed that equates accelerate-go and accelerate-stop distances allows the maximum takeoff weight for dispatch from a given runway length. This is known as a “balanced field length.” The associated V1 speed is called the “balanced V1” and is the V1 speed listed in the QRH and the Flight Management Computer. The V1 speeds depicted for derated takeoffs are also “balanced V1” speeds.
When using reduced thrust for takeoff, the “assumed temperature” for a given runway (either the field limit weight or climb limit weight) dictates the maximum weight or assumed temperature to be used. When using derated thrust for takeoff, the derate must also take performance calculations into account. The resulting assumed temperature V1 is the equivalent “balanced V1” for that particular takeoff.
Takeoff gross weight must not exceed the climb limit weight, field limit weight, obstacle limit weight, tire speed limit, or brake energy limit.
FAR Takeoff
757-300
Note: The graphic above refers to dry runway conditions only. Refer to the AFM for detailed wet runway performance information.
Rejected Takeoff Decision
The total energy that must be dissipated during an RTO is proportional to the square of the airplane velocity. At low speeds (up to approximately 80 knots), the energy level is low. Therefore, the airplane should be stopped if an event occurs that would be considered undesirable for continued takeoff roll or flight. Examples include Master Caution, unusual vibrations or tire failure.
Note: Refer to the Rejected Takeoff NNM in the QRH for guidance concerning the decision to reject a takeoff below and above 80 knots.
As the airspeed approaches V1 during a balanced field length takeoff, the effort required to stop can approach the airplane maximum stopping capability. Therefore, the decision to stop must be made prior to V1.
Historically, rejecting a takeoff near V1 has often resulted in the airplane stopping beyond the end of the runway. Common causes include initiating the RTO after V1 and failure to use maximum stopping capability (improper procedures/techniques). Effects of improper RTO execution are shown in the diagrams located in the RTO Execution Operational Margins section, this chapter. The maximum braking effort associated with an RTO is a more severe level of braking than most pilots experience in normal service.
Rejecting the takeoff after V1 is not recommended unless the captain judges the airplane incapable of flight. Even if excess runway remains after V1, there is no assurance that the brakes have the capacity to stop the airplane prior to the end of the runway.
Rejected Takeoff Maneuver
The rejected takeoff (RTO) maneuver is initiated during the takeoff roll to expeditiously stop the airplane on the runway. The pilot not flying should closely monitor essential instruments throughout the takeoff roll and immediately announce abnormalities, such as “ENGINE FIRE”, “ENGINE FAILURE”, or any adverse condition significantly affecting safety of flight. The decision to reject the takeoff is the responsibility of the captain, and must be made prior to V1 speed. If the captain is the pilot not flying, he should initiate the RTO and announce the abnormality simultaneously.
Note: If the decision is made to reject, the flight crew should accomplish the procedure in the NNM chapter of the QRH.
During the rejected takeoff, the first officer calls “60 KNOTS” during deceleration. If the takeoff is rejected prior to the THR HOLD annunciation, the autothrottle should be disengaged as the thrust levers are moved to idle. If the autothrottle is not disengaged, the thrust levers advance to the selected takeoff thrust position when released. After THR HOLD is annunciated, the thrust levers, when retarded, remain in idle. For procedural consistency, disengage the autothrottles for all rejected takeoffs.
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本文链接地址：757 Flight Crew Training Manual 机组训练手册(29)
