This mode protects against thrust lever movement if a system fault occurs. Lack of the THR HOLD annunciation means the protective feature may not be active. If THR HOLD annunciation does not appear, no crew action is required unless a subsequent system fault causes unwanted thrust lever movement. As with any autothrottle malfunction, the autothrottles should then be disconnected and desired thrust set manually.
The THR HOLD mode remains engaged until another thrust mode is selected.
If full thrust is desired when THR HOLD mode is displayed, the thrust levers must be manually advanced. When making a V1(MCG)-limited takeoff, do not exceed the fixed derate thrust limit except in an emergency.
After the airplane is in the air, pushing a GA switch advances the thrust to maximum available thrust and GA is annunciated.
Typical Takeoff Tail Clearance
The following diagram and table show the effect of flap position on liftoff pitch attitude and aft fuselage clearance during takeoff. Additionally, the last column shows the pitch attitude for aft fuselage contact with wheels on runway and landing gear struts extended. For a discussion of tail strike procedures see chapter 8 and the Operations Manual.
Note: Use of flap 1 as a takeoff flap setting is restricted to airplanes delivered with this capability or to airplanes having flap 1 installed as a takeoff flap setting.
Model Flap Liftoff Attitude Minimum Tail Tail Strike Pitch
(degrees) Clearance Attitude
inches (cm) (degrees)
757-200 1 5 10.3 10.0 30 (76) 33 (84) 12.3
15 9.5 38 (97)
20 8.5 47 (119)
757-300 5, 15, 20 7.5 26 (66) 9.5
Note: Flaps 1 (-200) takeoffs have the least clearance. Consider using a larger flap setting for takeoffs at light gross weights.
Effect of Rotation Speed and Pitch Rate on Liftoff
Takeoff and initial climb performance depend on rotating at the correct airspeed and proper rate to the rotation target attitude. Early or rapid rotation may cause a tail strike. Late, slow, or under-rotation increases takeoff ground roll. Any improper rotation decreases initial climb flight path.
An improper rotation can have an effect on the command speed after liftoff. If the rotation is delayed beyond V2 + 15, the speed commanded by the flight director is rotation speed up to a maximum of V2 + 25. An earlier liftoff does not affect the commanded initial climb speed, however, either case degrades overall takeoff performance.
Slow or Under Rotation (Typical)
Center-Of-Gravity (C.G.) Effects
When taking off at light weight and with an aft C.G., the combination of full thrust, rapid thrust application, and sudden brake release may tend to pitch the nose up, reducing nosewheel steering effectiveness. With C.G. at or near the aft limit, maintain forward pressure on the control column until 80 knots to increase nosewheel steering effectiveness. Above 80 knots, relax the forward control column pressure to the neutral position. At light weight and aft C.G., use of reduced thrust and rolling takeoff technique is recommended whenever possible. The rudder becomes effective between 40 and 60 knots.
Crosswind Takeoff
The crosswind guidelines shown below were derived through flight test data and engineering analysis.
Note: Engine surge can occur with a strong crosswind component if takeoff thrust is set prior to brake release. Therefore, the rolling takeoff procedure is strongly advised when crosswind exceeds 20 knots.
Takeoff Crosswind Guidelines
Crosswind guidelines are not considered limitations. Crosswind guidelines are
provided to assist operators in establishing their own crosswind policies. Takeoff crosswind guidelines are based upon the most adverse airplane loading (light weight and aft center of gravity) and assume an engine out RTO. On slippery runways, crosswind guidelines are a function of runway surface condition, and assume proper pilot technique.
中國航空網 www.k6050.com
航空翻譯 www.aviation.cn
本文鏈接地址：757 Flight Crew Training Manual 機組訓練手冊(26)
