Instrument System Failure Recognition and Pilot Response
Recognition
Failures present as abnormal indications, flagged or blank displays, disagreement between instruments, or aural/visual warnings. The core technique is cross-checking independent sources: standby instruments, the other pilot's displays, GPS, and outside visual references. A single instrument failure should never be acted on until confirmed by a second source.
Common scenarios and responses
- Pitot-static failure: identify which source is blocked (see domain 2), use standby and attitude/power, notify ATC.
- Gyro failure: the attitude indicator may tumble or show a slow drift; cross-check with the turn coordinator, standby attitude and visual horizon. Do not chase a failed instrument.
- Display failure: select reversionary mode, use standby instruments, follow QRH.
- Electrical failure: standby instruments on battery; shed load as required.
- Engine instrument anomaly: cross-check with performance and other parameters; a single sender failure is common.
Pilot response principles
- Fly the aircraft - maintain attitude, power and configuration.
- Analyse - use the QRH and cross-check.
- Decide and act - follow the checklist, inform ATC, and plan the approach.
Worked example
In IMC, the attitude indicator shows a slowly increasing bank while the turn coordinator is centred and the standby attitude shows wings level. The most likely cause is a drifting or partially failed primary attitude gyro. Correct action: disconnect the autopilot if it is following the faulty source, fly on the standby attitude and turn coordinator, and advise ATC.
Traps
Questions often present a plausible but wrong response, such as "immediately follow the failing instrument" or "assume the standby is wrong". Always prioritise attitude, power and cross-check.