On 9 May 2010, Boeing 737-800 being operated by Swedish operator Viking Airlines on a public transport charter flight from Sharm el Sheikh, Egypt to Manchester UK and which had earlier suffered a malfunction which affected the level of redundancy in the aircraft pressurisation system, experienced a failure of the single air conditioning pack in use when over southern Austria and an emergency descent and en route diversion to Vienna were made. There were no injuries to any of the 196 occupants.
An Investigation was carried out by the UK AAIB. It was established that the flight was a line training detail for the Captain occupying the left hand seat who had been designated as PF for the flight with the Line Training Captain occupying the co pilots seat.
It was eventually found that a left WING-BODY OVERHEAT annunciation which had occurred at 6500ft in the climb had been false. However, this was not known to the crew who had carried out the applicable Quick Reference Handbook (QRH) drill which required that the left hand air conditioning pack be shut down. Since there were no restrictions on continued flight with just a single pack, it was decided to continue the flight as planned.
Then, approximately 3.5 hours into the flight, in the cruise at FL360, the right air conditioning pack failed and cabin pressurisation was lost. The flight crew donned their oxygen masks, declared a MAYDAY and performed an emergency descent. An uneventful diversion to Vienna followed.
Following a ferry flight unpressurised to a UK maintenance base, a full engine engineering investigation was carried out during which various individually minor faults were found with the air conditioning and pressurisation system. It was concluded that the initial annunciation of an overheat had occurred because of a fault in the related firewire and that the subsequent pack failure which precipitated complete loss of pressurisation had resulted from the sudden failure of a flexible air hose for reasons which it was not possible to determine.
The Final Report of the Investigation was published on 9 September 2010 and may be seen at SKYbrary bookshelf: AAIB Bulletin: 9/2010 EW/C2010/05/01
No Safety Recommendations were made.