Malev B738 near Budapest on Nov 23rd 2011, oxygen masks released

A Malev Hungarian Airlines Boeing 737-800, registration HA-LOK performing flight MA-102 from Budapest (Hungary) to Moscow Sheremetyevo (Russia), was climbing through FL160 out of Budapest when the passenger oxygen masks were released although all air conditioning indications remained normal. The crew descended the aircraft to FL100 and returned to Budapest's runway 31R for a safe landing.

A replacement Boeing 737-800 registration HA-LOM reached Moscow with a delay of 105 minutes.

The Hungarian Transportation Safety Board (KBSZ) reported on Feb 2nd 2012, that both air conditioning systems were not working because the switches had not been turned on. When the aircraft reached FL170 the cabin pressure horn activated with the cabin altitude climbing through 10,000 feet. The crew however still did not turn the air conditioning systems on nor did they initiate an emergency descent, so that the cabin altitude climbed through 14,000 feet causing the passenger oxygen masks to be automatically released. At that point the crew decided to turn around and returned to Budapest.

The KBSZ released their final report concluding the probable causes of the incident were:

The technical investigation of the IC concluded that the incident happened due to the following provable reasons:

– After engine start, the crew failed to turn the “Pack” switches of the air conditioning system from the “OFF” position to the “AUTO” position.

– The failure to turn on air conditioning was also not recognized while reading out the checklists.

– When the horn indicating dangerously low cabin pressure went off, the crew did not recognize and eliminate the cause of pressure loss.

– The checklist applicable in case of the horn indicating dangerously low cabin pressure going off, does not include checking the air conditioning switches, and turning them on, if necessary.

– In spite of not having been able to eliminate the cause of the loss in pressure in the 3 minutes after the sound warning, the crew did not follow the procedure laid down in the emergency checklist applicable in case of the sound warning going off.

– The Final Report investigating the serious aviation incident of some years ago established that the activities of the crew led by the same commander swerved at several points from the relevant specifications.

– Following the earlier serious aviation incident, the commander did not undergo an unscheduled medical examination, thus his possible medical inadequacies which might have contributed to the occurrence may have remained hidden.