MD-11 Flight Crew Operations Manual
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Flight Controls -
Description and Operation
Flt.10.10
4. Manual trim, using the LONG TRIM handles. Override of the electrical trim
systems is accomplished with a pair of LONG TRIM suitcase style handles
on the Captain's side of the forward pedestal. The LONG TRIM handles
remain stationary when the control wheel switches operate trim. Use of these
handles disconnects the autopilot from any engaged mode (except DUAL or
SINGLE LAND).
Longitudinal Stability Augmentation System (LSAS)
The Longitudinal Stability Augmentation System (LSAS) enhances longitudinal
stability and provides:
• Pitch attitude hold.
• Pitch attitude limiting.
• Pitch rate damping.
• Pitch attitude protection.
• Positive nose lowering.
• Speed limiting.
• Stall protection.
Each FCC contains two LSAS control channels. This provides four redundant
channels of control. LSAS operates through series control of the elevators (no
movement of control column), and is inhibited when autopilot is engaged.
With less than 2 pounds of force applied on the control column, LSAS holds pitch
attitude by deflecting the elevators up to +/-5°. LSAS provides automatic
horizontal stabilizer trim to off load steady-state elevator displacement, restoring
a full 5° of elevator authority. Whenever there is more than 2 pounds of force on
the control column, pitch attitude hold function is inhibited and the aircraft rotates
in proportion to the applied force. When force is then removed from the column,
the aircraft holds the new pitch attitude. Pitch attitude hold is inhibited at bank
angles exceeding 30° or below 100 feet RA.
Pitch Attitude Limiting (PAL) ensures that LSAS will only hold a pitch attitude
between 30° ANU and 10° AND.
Pitch Rate Damping (PRD) increases the apparent static stability to reduce the
chance of overcontrol in pitch, especially at high altitudes. It is active throughout
the flight envelope, below 16,500 feet at 30% of the maximum damping
(FCC-908) increasing linearly to 100% above 20,000 feet.
Pitch Attitude Protection (PAP)(FCC-908) reduces the chance of a tail strike
during take-off and landing by adding nose down elevator if the aircraft is at
serious risk of tail contact with the ground. PAP is a direct function of pitch
attitude, radio altitude and pitch rate and is enabled below 100 feet RA. The pitch
attitude limit will vary linearly from 30° at 40 feet RA to 9.5° at 0 feet RA.
October 02, 2006
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