B757_Autothrottle_Use_With_Autopilot_Off
<P>B757_Autothrottle_Use_With_Autopilot_Off</P><P> </P>
<P>**** Hidden Message *****</P> 757.1<BR>Autothrottle Use<BR>with Autopilot Off<BR>Bill McKenzie<BR>Flight Crew Operations<BR>Boeing Commercial Airplanes<BR>May 2004<BR>The Boeing Company 757.2<BR>Autothrottle Use W/Autopilot Off<BR>What Is Pitch Coupling<BR>• The thrust vector for engines mounted under the wing will<BR>cause the airplane to pitch up with increasing thrust and<BR>pitch down with a reduction in thrust. When an autothrottle<BR>makes changes in gusty conditions it causes unwanted<BR>pitch changes.<BR>• Example: Imagine you are in level flight with autothrottle on,<BR>autopilot off, and a brief wind change causes a reduction in<BR>airspeed. The autothrottle will slightly advance the throttles to<BR>maintain commanded speed. This in turn will cause a slight<BR>aircraft pitch change upwards. The autothrottle will respond to<BR>the subsequent speed loss by increasing thrust further, resulting<BR>in further pitch up. The pilot will then correct by decreasing pitch<BR>attitude to descend back to the assigned altitude. As airspeed<BR>increases, thrust will decrease causing a further pitch down<BR>resulting in a descent through the desired altitude. The end<BR>result is a pitch “PIO” above and below the desired altitude.<BR>The Boeing Company 757.3<BR>Autothrottle Use W/Autopilot Off<BR>Some Advantages<BR>• Stabilized speed during approach<BR>• Speed floor protection<BR>• Allows pilot focus on visual maneuvering<BR>• Reduces necessity of wind additives (assumes autoland)<BR>for shorter landing distances<BR>Note: With a headwind additive, the actual landing distance would<BR>still be less than a planned 0 wind distance.<BR>The Boeing Company 757.4<BR>Autothrottle Use W/Autopilot Off<BR>Some Disadvantages<BR>• Excessive airspeed landing in gusts and turbulence<BR>• Potential pitch coupling close to the ground<BR>• Additional MCP coordination<BR>• Excessive unexpected throttle movement<BR>• Less thrust awareness (out of loop)<BR>• Airspeed crosscheck skills not exercised<BR>The Boeing Company 757.5<BR>Autothrottle Use W/Autopilot Off<BR>Flight Crew Training Manual<BR>• Landing (Previous Words)<BR>• When using autothrottle, position command speed to<BR>VREF + 5 knots. Sufficient wind and gust protection is<BR>available with autothrottle engaged because the<BR>autothrottle adjusts the approach speed upward to<BR>account for the wind gusts actually encountered during the<BR>approach.<BR>The Boeing Company 757.6<BR>Autothrottle Use W/Autopilot Off<BR>Flight Crew Training Manual<BR>Landing (New words)<BR>• When using autothrottle, position command speed to<BR>VREF + 5 knots. Sufficient wind and gust protection is<BR>available with autothrottle engaged because the<BR>autothrottle adjusts thrust rapidly when the airspeed<BR>drops below command speed while reducing thrust<BR>slowly when the airspeed exceeds command speed.<BR>In turbulence, the result is that average thrust is<BR>higher than necessary to maintain command speed.<BR>This results in an average speed exceeding command<BR>speed.<BR>The Boeing Company 757.7<BR>Autothrottle Use W/Autopilot Off<BR>Incidents<BR>• Boeing training pilots have repeatedly observed pitch<BR>coupling cause destabilized manual approaches on short<BR>final.<BR>• While infrequent, it is particularly hazardous when it<BR>occurs in unstable air, close to the ground.<BR>• Several hard landing incidents have been reported over<BR>the years.<BR>The Boeing Company 757.8<BR>Autothrottle Use W/Autopilot Off<BR>737 NG Incident<BR>• The gusts, turbulence and autothrottle engagement<BR>contributed to an unstabilized manual final approach.<BR>• At 0.6 miles and 14.4 seconds to touchdown, the<BR>“glideslope” warning sounded.<BR>• Over control of pitch attitude started after a high rate of<BR>descent occurred at 100 ft at 0.25 miles and 5.4 seconds<BR>from touchdown, causing a “sink rate” warning.<BR>• Over control continued throughout the flare. Nose landing<BR>gear collapsed.<BR>The Boeing Company 757.9<BR>Picture collapsed Nosegear<BR>Flight Operations Safety 􀀋<BR>737 Nosegear Collapsed on Landing<BR>The Boeing Company 757.10<BR>Autothrottle Use W/Autopilot Off<BR>737 NG Incident<BR>cont’d<BR>• 3.1.8 The autothrottle remained engaged after manual<BR>control was initiated on the approach, and remained<BR>engaged until after the touchdown, when it disconnected.<BR>• The gusts and turbulence contributed to over control of<BR>the pitch attitude during the flare resulting in a hard<BR>touchdown. The aircraft pitched down. This caused the<BR>aircraft to contact the ground nose gear first, with a<BR>longitudinal deceleration of 0.4 G. Shortly thereafter, the<BR>main gear contacted the ground coincident with a vertical<BR>load factor of 3.8 G.<BR>The Boeing Company 757.11<BR>Autothrottle Use W/Autopilot Off<BR>747 Incident (Canada)<BR>• Hard landing. Lost all the primary flight displays plus<BR>significant other damage.<BR>• Cause: 15kt HW gust just prior to flare, throttles went to<BR>idle with consequent pitch down.<BR><BR>The Boeing Company 757.12<BR>Autothrottle Use W/Autopilot Off<BR>Recommendation<BR>• Use manual thrust control when in manual flight due to<BR>potential “pitch coupling”<BR>• Unable to provide NTOs due to accident & incident history<BR>The Boeing Company 757.13<BR>Autothrottle Use W/Autopilot Off<BR>Risk Mitigation<BR>• Autothrottle disconnect altitude no lower than (300?) feet<BR>• Not with gusty winds or turbulence<BR>• Establish a procedure in case of sudden thrust increases<BR>and the landing becomes unstabilized<BR>• Provide training on pitch coupling<BR>• Establish Clear policy<BR>The Boeing Company 757.14<BR>Questions<BR>The Boeing Company 757.15<BR>Autothrottle Use W/Autopilot Off<BR>Boeing Flight Crew Training Manual<BR>• If the autothrottle is disengaged, or is planned to be<BR>disengaged prior to landing, the recommended method for<BR>approach speed correction is to add one half of the<BR>reported steady headwind component plus the full gust<BR>increment above the steady wind to the reference speed.<BR>One half of the reported headwind component can be<BR>estimated by using 50% for a direct headwind, 35% for a<BR>45° crosswind, zero for a direct crosswind and<BR>interpolation in between.<BR>The Boeing Company 757.16<BR>Autothrottle Use W/Autopilot Off<BR>737 NG Accident<BR>• 3.1.7 An ILS approach was flown to Rwy XX. DFDR data show that pitch attitude<BR>averaged near 0º during the initial coupled approach, which was appropriate for the<BR>airspeed, gross weight and flap setting. The glide slope and localizer were tracked to<BR>within tolerances until the final approach segment. At 3.5 miles from touchdown the<BR>autopilot was disengaged. Pitch excursions from –3.3º to 3.5º were present throughout<BR>the final approach. A crosswind heading correction of approximately 5ºnose left was<BR>maintained at touchdown.<BR>• 3.1.8 The autothrottle remained engaged after manual control was initiated on the<BR>approach, and remained engaged until after the touchdown, when it disconnected.<BR>• 3.1.9 The 737 Flight Crew Training Manual (FCTM), Reference C, page 2.8, states:<BR>“when in manual flight, manual thrust control is recommended”. The approach was<BR>flown using autothrottle while in manual flight, contrary to the FCTM recommendation.<BR>• 3.1.10 The gusts, turbulence and autothrottle engagement contributed to an unstabilized<BR>final approach under manual control. At 0.6 miles and 14.4 seconds to go to touchdown<BR>the “glideslope” warning sounded. Overcontrol of the pitch attitude started after a<BR>high rate of descent occurred at 100 ft at 0.25 miles and 5.4 seconds from<BR>touchdown, causing a “sink rate” warning. Overcontrol continued throughout the<BR>flare.<BR>• 3.1.11 This led to a hard first ground contact and rebound, followed by a large forward<BR>pilot control input to a negative pitch angle of – 3.5º. A go-around was apparently<BR>attempted but this was quickly discontinued. 谢谢楼主~~顶一个~~
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