What is the maximum allowable altimeter difference between PFDs on the ground?

The maximum allowable altimeter difference between the Primary Flight Displays (PFDs) on the ground is 75 feet. This specification is important for ensuring that both pilots have a consistent reference for altitude during ground operations. A difference within this limit indicates that both altimeters are functioning correctly and are calibrated similarly, which is crucial for maintaining safety and situational awareness, particularly during taxi and takeoff procedures. An altimeter discrepancy exceeding 75 feet could indicate a malfunction or miscalibration, which may lead to incorrect altitude references and potentially hazardous situations during flight. Therefore, the 75-feet limit serves as a critical threshold that pilots must be aware of before proceeding with their flight preparations.