Max in-flight difference between pilot and copilot altitude displays

• A. 100 feet
• B. 200 feet
• C. 300 feet
• D. 400 feet

Answer: (B)

In flight, both pilots rely on their primary altitude displays to stay aligned with the aircraft’s true altitude. The limit is set so that any difference between the pilot’s and copilot’s altitude readouts is small enough to ensure they both have a consistent altitude reference, reducing the risk of incorrect altitude decisions.

A discrepancy up to two hundred feet is considered acceptable because it accounts for normal instrument tolerances and display update timing, while still being tight enough to catch meaningful instrument or setting errors. If the difference grows beyond this limit, it signals a potential instrument fault, pressure-setting mismatch, or data source issue, and crews are expected to cross-check with standby sources and follow abnormal procedures to restore agreement.

Why not smaller or larger limits: a one hundred foot gap is often too restrictive given routine cockpit variances and transient reading differences, while gaps of three hundred or four hundred feet could allow substantial altitude disagreement that jeopardizes safe separation and approach performance.