Swedish regional carrier Malmo Aviation has amended its BAE Systems Avro RJ100 checklists after one of its crews continued a climb towards cruise altitude without realising the jet was not pressurised.

Both air conditioning packs were off, but this was missed during the climb checklist. A cockpit indicator also showed that the avionics fan was off – an alert which can be triggered by low air pressure – but the abnormal checklist procedure for such warnings did not specify any actions.

The RJ100, en route from Stockholm Bromma to Gothenburg, was climbing towards its cruising altitude of 28,000ft at the time. It had reached about 18,000ft when flight attendants told the pilots that oxygen masks had deployed in the passenger cabin.

In response the pilots put on oxygen masks and, with the aircraft at about 19,000ft, initiated a descent. The aircraft continued to Gothenburg; there were no injuries among the 42 passengers and five crew members.

Swedish accident investigation agency SHK, which describes the incident as “serious”, is unable to confirm whether the air conditioning packs which pressurise the aircraft were switched on during take-off.

But SHK says RJ100 pilots sometimes need to adjust the air-supply configuration in order to gain maximum efficiency from the engines under certain conditions. It adds that the crew switched the jet’s engine de-icing systems on and off several times during the climb, owing to changing weather, and says: “It is possible, even though not probable, that confusion could have taken place at some moment.”

Whatever the reason, the switches for the air conditioning packs were left in the ‘off’ position. While the packs are supposed to be checked as part of the climb checklist, the checklist at the time only contained a summary entry regarding the air supply – the full details featured only in the expanded checklist.

“We are of the opinion that the checklist was not clear enough to prevent continued climbing without the cabin being pressurised,” says SHK. Although the checklist is supposed to prevent a climb in such circumstances, the agency says: “In this particular flight this barrier did not work.”

Nearly half of the 43 oxygen-mask hatches installed on the aircraft, 20 in all, failed to open during the event. They had deployed properly during a C-check about three weeks before but the masks had subsequently been repacked incorrectly.

The investigators also found that, during the incident, cabin crew could not find the small tool designed to open stuck hatches.

SHK adds that a damaged cabin pressure sensor contributed to the event and is recommending that European regulators reduce the inspection interval for such components.

Source: flightglobal.com's sister premium news site Air Transport Intelligence news

Source: FlightGlobal.com