Final answer:
Elevator thrust compensation (ETC) is part of FADEC and adjusts the elevator deflection in response to thrust setting changes, using N1, Mach Number, and Pressure Altitude as inputs. A 'ELEV THR COMP FAIL' message indicates a system failure due to unavailable inputs.
Step-by-step explanation:
FADEC (Full Authority Digital Engine Control) includes a feature called elevator thrust compensation (ETC), which adjusts the elevator deflection based on the thrust lever angle (TLA) to help maintain pitch control during varying power settings. This adjustment is limited to a range of +/- 5 degrees. The Flight Control Module (FCM) calculates ETC based on three critical inputs: engine N1 (the low-pressure compressor speed), Mach Number, and Pressure Altitude. If any of these inputs are unavailable, a 'ELEV THR COMP FAIL' message will alert the pilot to the system failure. Understanding these systems is essential for the safe and efficient operation of modern aircraft.