AAIB Links ATR 42-500 Display Failure to Faulty Contactor

The UK's Air Accidents Investigation Branch (AAIB) has published its final report on a serious incident involving an ATR 42-500, identifying a faulty electrical contactor as a key contributing factor to a momentary flight deck display failure. The investigation into the flight deck display failure has prompted new safety actions from the aircraft manufacturer and the European Union Aviation Safety Agency (EASA) to address the potential ATR 42-500 electrical fault.

The incident, which occurred on August 27, 2022, involved aircraft G-LMRC, a turboprop operated by Loganair. The flight was in its initial climb out of Aberdeen Airport with 25 passengers and 3 crew members on board when the event took place. The AAIB's findings highlight the critical interdependencies within modern avionics and aircraft electrical systems, where a single component issue can have significant operational consequences.

Incident Details

According to the official AAIB report, the aircraft was passing through 10,000 feet (Flight Level 100) when the flight crew experienced a near-total loss of primary flight displays. Both the captain's and first officer's Electronic Attitude Director Indicator (EADI) and Electronic Horizontal Situation Indicator (EHSI) screens went blank. The cockpit display blackout, which also affected other systems, lasted for approximately 3 seconds before power was restored and the displays returned to normal functionality.

The flight crew declared a PAN-PAN, discontinued the climb, and returned to Aberdeen Airport without further incident. No injuries were reported among the passengers or crew. The prompt and professional actions of the flight crew were commended in managing the unexpected and critical loss of instrumentation.

Investigation Findings

Following the event, the AAIB launched a comprehensive aviation safety investigation. While investigators were unable to determine the definitive root cause of the transient electrical interruption, their analysis pointed to a critical component failure. The investigation found a fault in the 1PA contactor, a device responsible for switching to a backup electrical source in the event of a primary power failure.

Testing revealed the contactor was stuck and therefore unable to supply backup power from the Direct Current Bus 2 (DC BUS 2) when the primary supply was momentarily lost. The report notes that the source of the initial power interruption remains undetermined, but the failure of the backup system to engage was a direct contributor to the loss of the flight displays. The AAIB's analysis of the aircraft's systems and historical data suggests a vulnerability within the aircraft electrical systems architecture.

Regulatory and Manufacturer Response

In response to the G-LMRC incident report, both the aircraft manufacturer, ATR, and the regulatory body, EASA, have taken action. The AAIB issued one Safety Recommendation to ATR to continue its investigation into the possible causes of the electrical failure to prevent future occurrences.

Concurrently, EASA and ATR have implemented safety actions that mandate the testing and, if necessary, replacement of 1PA contactors that have failed operational checks. This issue has been previously addressed by EASA through Emergency Airworthiness Directive AD 2021-0120-E, which required tests of the 1PA contactor on certain ATR models. The AAIB inquiry also referenced three similar, though not formally investigated, electrical-failure events on ATR -500 variants that occurred in 2018 and 2019, indicating a potential pattern of avionics vulnerability.

A spokesperson for Loganair acknowledged the report's findings, stating: “We acknowledge the report published this morning concerning an event from 2022. While the recommended actions are with the aircraft manufacturer, we will continue to work with all parties involved to support as is appropriate. We thank our pilots and cabin crew who acted in an exemplary manner. As always, the safety of our customers and crew remains our highest priority.”

Why This Matters

This incident and the subsequent AAIB report on the ATR 42-500 underscore the critical reliance of modern glass cockpits on stable and redundant electrical power. The failure of a single, relatively simple component like a contactor demonstrated its potential to disable multiple primary flight instruments simultaneously. The resulting EASA safety action serves as a reminder of the continuous feedback loop required between accident investigators, manufacturers, and regulators to identify and mitigate systemic risks in regional aircraft safety.

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