Flybe DH8D enroute on Sep 21st 2018, loss of cabin pressure

Last Update: July 11, 2019 / 14:20:52 GMT/Zulu time

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Photo of Flybe G-PRPC, De Havilland Dash 8 (400) — Flybe G-PRPC, De Havilland Dash 8 (400) (Photo credit: Riik@mctr / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Sep 21, 2018

Classification
Incident

Cause
Loss of cabin pressure

Airline
Flybe

Flight number
BE-694

Departure
Belfast City, United Kingdom

Destination
Edinburgh, United Kingdom

Aircraft Registration
G-PRPC

Aircraft Type
De Havilland Dash 8 (400)

ICAO Type Designator
DH8D

A Flybe de Havilland Dash 8-400, registration G-PRPC performing flight BE-694 from Belfast City,NI to Edinburgh,SC (UK) with 70 passengers and 4 crew, had just levelled off a cruise level 170 when the crew received a tripple chime warning and the cabin pressure indication illuminated. The crew initiated a rapid descent to FL100 declaring Mayday, during the descent the crew noticed that the switches for both the air conditioning systems were set to OFF. The crew activated both packs, the cabin began to pressurize. After levelling off at FL100 the crew consulted with dispatch and cabin, cabin crew advising the passenger were unaware of the occurrence. The crew decided to continue the flight to Edinburgh at FL100 and landed safely at the destination.

The UK AAIB released their bulletin concluding the probable cause of the serious incident was:

The aircraft departed Belfast with both air conditioning systems off and therefore did not pressurise. The fact that the systems were off was not detected during routine checks before departure. 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 AAIB described the sequence of events:

During the previous sector the crew had difficulty in controlling the flight deck and cabin temperature, causing passenger and crew discomfort. During a busy turnaround, the commander therefore undertook a reset of the air conditioning packs using the Q400 ‘Supplemental Procedure Ground Reset Guide’. The crew completed their procedures and departed from Belfast City Airport at 1805 hrs.

The departure was routine and the aircraft climbed to its planned cruise level of FL170. Shortly after reaching cruise level, at 1825 hrs the flight deck triple chime audio warning sounded and the cabin pressure warning illuminated. The flight crew immediately checked the cabin altitude and, when they confirmed that it was above 10,000 ft, they actioned the ‘Rapid Depressurisation and Emergency Descent’ checklist from the QRH. A MAYDAY was declared.

During the descent the crew reviewed their actions and noticed that both air conditioning pack switches were selected to off. They selected both packs on and the aircraft began to pressurise. The aircraft levelled at FL100 just to the south of Glasgow. The cabin crew were informed of the situation but they told the flight crew that the passengers were unaware of the event (the Q400 has no passenger oxygen masks to drop down in front of passengers).

Via the handling agent in Edinburgh, the crew asked their operations department if they should continue to Edinburgh or return to Belfast. The company wanted them to continue to Edinburgh, and the flight arrived there at 1855 hrs.

The AAIB analysed:

During the turnaround preceding the incident sector the crew workload was influenced by numerous factors including a change in planned destination and issues with catering. These factors led to both flight crew members being absent from the flight deck for periods of time during the turnaround. As a consequence, their ability to work effectively as a team and trap each other’s errors was significantly diminished.

The temperature control problem which the crew encountered in the preceding sector caused issues with both crew and passenger comfort. Due to the discrepancy in the maintenance system, however, the crew were unaware of the relevant technical issue. In an effort to resolve the problem during the turnaround, the commander undertook the reset procedure from the Q400 ‘Supplemental Procedure Ground Reset Guide’, but the conduct of the procedure added to the already elevated workload of the crew, and the commander was interrupted and it was not completed correctly.

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. 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. The aircraft did not, therefore, pressurise and the Cabin Altitude warning sounded shortly after reaching the cruise flight level.