Center AP 767 ?
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Join Date: Oct 2010
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Center AP 767 ?
Hye all
With some friends we were wondering if on the 767 we only use the center AP on flight and no one time the right one or left one , and if yes why ?
Does the 2 others Ap's are only used in the autoland procedure ?
Thanks for informations
Regards
With some friends we were wondering if on the 767 we only use the center AP on flight and no one time the right one or left one , and if yes why ?
Does the 2 others Ap's are only used in the autoland procedure ?
Thanks for informations
Regards
Join Date: Jun 2006
Location: Canada
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Read this. This is actually from a B757 AMM but fairly applicable to the B767.
Automatic Stabilizer Trim
The purpose of the Flight Control Computers (FCCs) in the stabilizer trim system is to provide trim commands when at least one channel of the autopilot is engaged. All three FCCs may be used; any one when in the cruise mode, or two or more when in the autoland mode. The left and right FCCs provide inputs to their respective SAMs. The center FCC provides inputs to both SAMs. Only one SAM is engaged at any time, with the first FCC engaged selected as the autotrim source. Priority for simultaneous FCC engagement is left, center, right.
The FCCs generate trim commands in response to an elevator deflection exceeding a preset authority threshold. Trim commands applied to the SAM cause the stabilizer to assume the elevator trim load. Stabilizer position signals are fed back to the FCCs from the associated Stabilizer Position Modules (SPM). Trim commands stop when the elevator is within the elevator authority threshold limits.
The FCC generates a digital trim engage discrete and a separate analog autotrim discrete. These cause the SAM to select the FCC as the active trim source. With any one FCC controlling, a single STCM hydraulic output drives the stabilizer motor at half-rate speed (0.1 degrees/sec to 0.25 degrees/sec). The elevator feel computer determines the pressure applied at the STCM, which determines stabilizer rate.
The three FCCS communicate with the SAM via ARINC 429 buses. Protocol logic within each FCC determines which computer trims the stabilizer. The FCCS monitor each other. In the autotrim mode, the command response monitor in FCC performs loop monitoring to detect autotrim failures. Autotrim failure occurs when stabilizer does not respond to computed commands, stabilizer movement is inconsistent with computed commands or when analog AUTOTRIM VALID from SAM becomes invalid. When a single autopilot is engaged, a detected autotrim failure which cannot be cleared by internal autosequencing (center FCC only) disables the active trim control path by disengaging the appropriate SAM. Since the center FCC interfaces with both SAMs, sequencing to another trim channel following a trim failure can occur only if the center FCC is engaged. When the center autopilot is engaged, the left SAM is always selected. A subsequent trim failure requires the FCC to inititate sequencing to the right SAM. When more than one autopilot is engaged, sequencing to another trim channel is attempted when the current SAM-driving autopilot disconnects, or the active trim control path fails as detected by the local command-response monitor. The FCC autosequencing cycle is left - Right - Center - Left.
The C A/P can automatically switch to the other SAM in case of a Stab trim issue. There is no need for the pilot to disengage an A/P and then reengage another to continue flying.
It is the prefered method of operating the B757, B767, and B747
Automatic Stabilizer Trim
The purpose of the Flight Control Computers (FCCs) in the stabilizer trim system is to provide trim commands when at least one channel of the autopilot is engaged. All three FCCs may be used; any one when in the cruise mode, or two or more when in the autoland mode. The left and right FCCs provide inputs to their respective SAMs. The center FCC provides inputs to both SAMs. Only one SAM is engaged at any time, with the first FCC engaged selected as the autotrim source. Priority for simultaneous FCC engagement is left, center, right.
The FCCs generate trim commands in response to an elevator deflection exceeding a preset authority threshold. Trim commands applied to the SAM cause the stabilizer to assume the elevator trim load. Stabilizer position signals are fed back to the FCCs from the associated Stabilizer Position Modules (SPM). Trim commands stop when the elevator is within the elevator authority threshold limits.
The FCC generates a digital trim engage discrete and a separate analog autotrim discrete. These cause the SAM to select the FCC as the active trim source. With any one FCC controlling, a single STCM hydraulic output drives the stabilizer motor at half-rate speed (0.1 degrees/sec to 0.25 degrees/sec). The elevator feel computer determines the pressure applied at the STCM, which determines stabilizer rate.
The three FCCS communicate with the SAM via ARINC 429 buses. Protocol logic within each FCC determines which computer trims the stabilizer. The FCCS monitor each other. In the autotrim mode, the command response monitor in FCC performs loop monitoring to detect autotrim failures. Autotrim failure occurs when stabilizer does not respond to computed commands, stabilizer movement is inconsistent with computed commands or when analog AUTOTRIM VALID from SAM becomes invalid. When a single autopilot is engaged, a detected autotrim failure which cannot be cleared by internal autosequencing (center FCC only) disables the active trim control path by disengaging the appropriate SAM. Since the center FCC interfaces with both SAMs, sequencing to another trim channel following a trim failure can occur only if the center FCC is engaged. When the center autopilot is engaged, the left SAM is always selected. A subsequent trim failure requires the FCC to inititate sequencing to the right SAM. When more than one autopilot is engaged, sequencing to another trim channel is attempted when the current SAM-driving autopilot disconnects, or the active trim control path fails as detected by the local command-response monitor. The FCC autosequencing cycle is left - Right - Center - Left.
The C A/P can automatically switch to the other SAM in case of a Stab trim issue. There is no need for the pilot to disengage an A/P and then reengage another to continue flying.
It is the prefered method of operating the B757, B767, and B747
