UK regional carrier Flybe has urged pilots to record faults promptly and in writing after incomplete reporting of a defect played a role in a De Havilland Canada Dash 8-400 not pressurizing because the aircraft was not configured correctly, a UK Air Accidents Investigation Branch (AAIB) report revealed.

The incident flight, from Belfast to Edinburgh, took place Sept. 21, 2018. The crew departed normally and leveled off at 17,000 ft. Shortly after entering cruise, the aircraft’s cabin-pressure warning light and aural chime activated, indicating the cabin was not pressurized. The crew followed the appropriate checklist and began an emergency descent. They soon realized both air conditioning packs were set to “off,” and turned them on. The aircraft began to pressurize. 

After consulting with the cabin crew—the Dash 8-400 is not required to have drop-down oxygen masks, and flight attendants reported that passengers were not aware of an issue—and airline personnel on the ground, the crew decided to continue to Edinburgh.

Investigators found the incident aircraft had an issue with the automatic cabin temperature control that had been deferred for repair, per the aircraft’s minimum equipment list. The crew did not know about the problem, however, because it was not noted in the aircraft’s onboard log—it only appeared in Flybe’s electronic maintenance system. While the report does not explain why, it suggests that the pilots who discovered the issue discussed it with mechanics but did not note it in the aircraft log.

The incident-flight pilots realized they had an issue with the cabin temperature during the previous segment. But because they were unaware of the deferred item, they did not know the specifics. 

During preparation for the Edinburgh departure, the captain—alone on the flight deck—decided to follow the manufacturer’s procedure to re-set the air conditioning system. But he had to leave the flight deck during the procedure to deal with a catering issue. A flight-plan change added to the crew’s pre-departure workload.

“When both pilots returned to the flight deck they were keen to try and make an on-time departure despite the issues that had affected the turnaround,” the AAIB wrote. “Their workload was now significantly above the norm and while they believed they had completed all the relevant checklist actions correctly, it became apparent later that both air conditioning systems had been left selected off.”

While the AAIB noted that a thorough pre-flight check could have detected the mis-configuration, it underscored that several factors helped set the stage for the mishap. 

“The effectiveness of the crew’s actions was reduced by the high workload resulting from operational factors and by their attempts to deal with the symptoms of a technical issue with the aircraft, which had not been communicated to them,” the report said.

Flybe used an internal newsletter to emphasize the need to follow the defect-reporting procedure.

“It’s really important that all cabin defects are recorded as and when they are noticed,” the airline said. “It’s not enough to pass things on to the line engineers verbally—a formal record is the only reliable method of ensuring that the issue will be dealt with.”

Sean Broderick, sean.broderick@aviationweek.com