FAA Instrument Rating Airplane (IRA)Flight Instruments and SystemsHard
On a glass cockpit aircraft, the primary Air Data Computer (ADC) fails, causing loss of airspeed, altitude, and vertical speed data on the pilot's Primary Flight Display (PFD). According to typical glass cockpit system design, what is the appropriate pilot action?
- ASelect the reversionary display mode to present standby or copilot-side ADC data on the PFD
- BRecognize that no backup exists and initiate an immediate diversion
- CRely solely on GPS groundspeed readouts as a permanent substitute for airspeed
- DDisengage the autopilot and revert entirely to magnetic compass navigation
Show answer & explanationAnswer & explanation
Correct answer: A. Select the reversionary display mode to present standby or copilot-side ADC data on the PFD
Modern glass cockpit avionics suites include reversionary modes that allow the pilot to display data from a standby air data computer or the other side's ADC/PFD onto the affected display, restoring critical flight instrument information after a single ADC failure.
Why the other options are wrong
- B. Most glass cockpit aircraft have redundant air data sources, making immediate diversion unnecessary if reversion succeeds.
- C. GPS groundspeed is not a substitute for calibrated airspeed and doesn't restore altitude/VSI data.
- D. Autopilot disengagement is not automatically required, and compass-only navigation is unrelated to restoring air data.
Reversionary Display Mode
A glass cockpit feature allowing display of data from a standby or alternate air data/attitude source onto an affected PFD after failure of the primary source, restoring critical flight instruments.
- Typically activated via a reversionary panel switch or button
- Common in integrated avionics suites (e.g., G1000-type systems)
- Does not require diversion if the reversion successfully restores needed data
Memory trick: When one screen goes dark, 'flip the switch' to borrow the other side's data.