MD-11 Flight Crew Operations Manual
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Automatic Flight -
Description and Operation
Auto.10.27
This typical mode sequencing for the two speed protection modes is affected by
specific flight conditions and by throttle position. If the throttles are already
positioned at an appropriate thrust limit for the speed limit being violated, the FCC
will not wait until Vmin-10 (or Vmax+10) to engage SOP speed protection. The
following example is provided to clarify this operation.
1. Aircraft is in a Vmax-5 knot descent. Autopilot is on, autothrottles are off,
and throttles are at idle.
2. Aircraft begins to exceed Vmax.
3. Since throttles are already at idle, SOP speed protection comes on not later
than Vmax+5. Throttles remain at idle, elevator motion pitches the nose up,
and the aircraft decelerates.
Longitudinal Stability Augmentation System (LSAS)
Changes provide enhanced commonality between trijet-model approach/landing
handling characteristics and control column force deterrent as the aircraft is
rotated to near tail-strike pitch attitudes during takeoff and landing. These
changes, referred to as Low Altitude Stability Enhancement (LASE), are as
follows:
1. Modified Pitch Rate Damper (PRD) - The existing high-altitude PRD
operates throughout the entire flight envelope. The PRD will continue to
provide 30% of its high altitude pitch rate damping from 16,500 feet down
to field elevations.
2. New Pitch Attitude Protection (PAP) Subfunction - The LSAS control law
will implement a pitch attitude limiting function that will be enabled below
100 feet radio altitude. As with all LSAS elevator commands, the PAP will
be limited to a total of 5 degrees of elevator authority. The PAP subfunction
will be further limited to only command nose-down elevator displacements.
If the aircraft approaches a tail strike pitch altitude, the pilot-flying will
perceive the effect of PAP as an increase in the control column force
required to maintain the pitch attitude. The pitch attitude limit used by PAP
will vary linearly from 30 degrees at 40 feet radio altitude down to a
minimum of 9.5 degrees at 0 feet radio altitude. The PAP subfunction will
be active for both takeoff and landing.
3. New Positive Nose Lowering (PNL) Subfunction - This new subfunction
will only be applied during landing phase, and will not affect AUTOLAND
operations or Auto Flight System (AFS) autoland performance. The PNL
subfunction will apply approximately 3 degrees of nose-down elevator
command at main wheel spinup, at the same time that the FCC commands
the Auto Ground Spoilers (AGS) to extend. As the spoilers extend beyond
10 degrees, the second phase of PNL will increase the nose-down elevator
command to approximately 4 degrees. This subfunction, in combination
with the enhanced PRD, will control the elevator to avoid aircraft nose-rise
after touchdown, and to assist in de-rotation.
October 02, 2006
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