B757_Autothrottle_Use_With_Autopilot_Off

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B757_Autothrottle_Use_With_Autopilot_Off

 

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

hehe1019

谢谢楼主~~顶一个~~

漫步007

THX。。。。。。