744 maneuvre margin question

[Spanner Turner]

The description below is for the Stall Warning Management Computer on a 747-400. Speedbird716, you are correct - the IRS does input into the computation for minimum manouvering speed and it does exist in a textual form. (I found some old stone tablets out the back of the hangar with this info chiseled into them) The IRS provides a pitch acceleration value for the min manouv margin. The generation of the yellow pitch limit indicator on PFD is described in the paragraph on Arinc 429 outputs. It also drives the speed tape limits (max/min manouver speeds) I shall try and dig out a better description of this. Hope this helps.

Stall Warning Management Computer Inputs
The Stall Warning Management Computer (SWMC) cards gather
information from many sources to evaluate and determine stall onset.
These sources include information derived both directly and
indirectly through other units.
Input sources include:
• Proximity Switch Electronic Unit (PSEU) information:
− Nose gear position.
• Flap Control Units (FCU) information:
− Flap position.
• Master Monitor cards information:
− Gear and flap, position from PSEU and FCUs, the cards control
power-up BITE.
• Spoiler position information:
− Spoiler deployment.
• Inertial Reference Units (IRU) information:
− Pitch acceleration.
• Air Data Computer (ADC) information:
− Angle of attack, speed/mach.
• CMC test:
− BITE test initiated by use of the CDU.


Stall Warning Management Computer Outputs
The SWMCs directly control the operation of the control column
stick shakers. They also provide information to:
1. The EFIS/EICAS Interface Units (EIUs),
2. Flight Management Computers (FMC) and Central Maintenance
Computers (CMC) via the EIUs.
3. The Ground Proximity Warning Computer (GPWC).


ARINC 429 Output
In addition to generating the alpha-max value for stick shaker
operation, the SWMC computes two types of parameters for ARINC
429 outputs. They are:

• Pitch limit parameters:
− SWMC calculation of pitch limit parameters are used to
indicate the maneuver margins available for the airplane to
recover from windshear condition without encountering stick
shaker warnings. This information is transmitted to the Ground
Proximity Warning Computer.
The same information will also be transmitted first to the
[]EFIS/EICAS Interface Units (EIUs) and then on to Flight
[]Management Computers (FMCs) for display of the Pitch Limit
Indicator (PLI) symbol on the Primary Flight Displays (PFDs).

• Speed Tape Parameters:
− The SWMC also generates various speed tape parameters such
as Vmo and Vss(stick shaker speed). This information is
transmitted to the FMCs via the EIUs.