HORIZONTAL STABILIZER CONTROL -FUNCTIONAL DESCRIPTION -STABILIZER ELECTRICAL CONTROL
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HORIZONTAL STABILIZER CONTROL -TRIM LIMITS
General
Structural stops and the travel limiter limit stabilizer movement mechanically. Electrical limit switches and the stabilizer position limit function in the PFCs limit stabilizer movement electrically.
Structural Stops
On the upper and lower portions of the stabilizer ball screw are structural stops that limit stabilizer travel to +4 degrees airplane nose down trim and -11 degrees airplane nose up trim.
Travel Limiter
Within the aft stabilizer quadrant assembly of the alternate stabilizer trim mechanism there are hammer and stops that keep stabilizer travel to a limit.
The mechanism forces the control lever of the alternate pitch trim levers back to the null position when the stabilizer reaches its travel limits.
The travel limits for operation with the alternate pitch trim levers are: +3.88 degrees airplane nose down trim and -10.88 degrees airplane nose up trim.
Limit Switches
In each of the three stabilizer position modules are two limit switches. One switch opens to stop stabilizer movement in the airplane nose up trim direction and the other stops stabilizer movement in the airplane nose down trim direction.
In the normal mode of operation, the limit switches restrict nose down trim if the flaps are not retracted. The PFCs control airplane nose down trim when the flaps are retracted.
The limit switch trim limits are +3.75 degrees nose down and -
10.75 degrees nose up.
PFC Limits
In the normal and secondary mode the PFCs supply limits to stabilizer movement.
With flaps retracted the PFCs limit stabilizer travel to +2.25 degrees airplane nose down to -10.25 degrees airplane nose up.
If the flaps are not retracted, the nose up PFC limitation remains at -10.25 degrees. The limit switches control the nose down limit at +3.75 degrees.
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HORIZONTAL STABILIZER CONTROL -TRIM LIMITS
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777 AIRCRAFT MAINTENANCE MANUAL
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BOEING PROPRIETARY -Copyright # -Unpublished Work -See title page for details.
HORIZONTAL STABILIZER POSITION INDICATION -GENERAL DESCRIPTION
Purpose The stabilizer position indicating system operates in normal,
secondary, and direct modes. The stabilizer position indication system measures the position of the stabilizer and sends this information to the ACEs. The ACEs send the information to the PFCs for stabilizer position calculation and control. The PFCs send the stabilizer position signals to the AIMS which controls the position indicators.
Stabilizer Position Indication
The three stabilizer position modules send signals to three ACEs. The ACEs change the signals from analog to digital and send them to the PFCs.
The PFCs use the position module signals to control the stabilizer position. The PFCs then send the stabilizer position signals to the AIMS. The AIMS sends them through the ARINC 429 bus to the stabilizer position indicators.
The AIMS also sets the green band display on each position indicator. The WEUs calculate which of the three green band segments to show on the position indicators. The WEUs use airplane weight, center of gravity position and engine thrust rating to calculate the green band display. The WEUs use a discrete signal from the nose gear pressure switch to verify the green band calculation. The calculated signals then go from the WEUs to the AIMS which selects and shows the green band on the stabilizer position indicators.
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HORIZONTAL STABILIZER POSITION INDICATION -GENERAL DESCRIPTION
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HORIZONTAL STABILIZER POSITION INDICATION -STABILIZER POSITION MODULE AND INDICATOR
Purpose
The stabilizer position modules send stabilizer position signals to the ACEs. From the ACEs, the digital signals then go to the PFCs. The PFCs use this data for two functions, stabilizer position indication and stabilizer control. The PFCs then send the stabilizer position indication to the AIMS.
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