BA2011-272-4P-1 In the course of the investigation, the IC has found, that when the cabin altitude horn went off, the crew started reading out the checklist only after a very extensive (several minutes long) delay, an even then it was not carried out in adherence to the requirements. According to the information provided to the IC, in simulations, the cases of pressure drop are presented to the pilots frequently under identical, conventional conditions, which only helps indirectly in recognizing and coping with real-life cases.

TSB recommends the Directorate for Air Transport of the National Transport Authority that it pay special attention to present, practice and test cases of cabin pressure loss under real-life conditions during the training and testing of commercial pilots.

As a result of the acceptance and execution of the recommendation the IC expects that in possible similar situations in the future the crew of the aircraft will handle the situation less belatedly, and in line with the requirements.

BA2011-272-4P-2 In the course of the investigation, the IC has been provided with information stating that in the recent years the pilots of the Boeing 737 aircrafts several times failed to turn the “Pack” switches of air conditioning from the “OFF” to the “AUTO” position after the engine start, and they did not recognize this failure even during reading out the checklists. On several airplane types a neutrally coloured light (e.g. white) is used to indicate conditions not in line with the usual status.

TSB recommends the Federal Aviation Administration and the European Aviation Safety Agency to consider using an alerting annunciation on the Boeing 737 aircraft, which would indicate to the pilots that air conditioning is not on.

As a result of accepting the recommendation, and applying the warning light, the IC believes that a decrease in the number of irregularities and serious incidents due to the inaccurate operation of air conditioning switches can be expected.

BA2011-272-4P-3 The investigation would have been greatly facilitated, if the momentary value of the cabin pressure/cabin altitude had been known in the course of the event.

TSB recommends the International Civil Aviation Organization to consider extending the data obligatorily recorded by the accident data recorder of the aircrafts to include the momentary value of cabin pressure.

As a result of accepting the recommendation, the IC expects that the occurrences related to cabin pressure can be investigated in a more efficient and effective way in the future, which will indirectly have a positive effect on flight safety as well.

BA2011-272-4P-4 The IC has found, that the procedure to be followed in case of the warning sound indicating a drop in the cabin pressure going off on the Boeing 737 type does not give an opportunity to check whether air conditioning is turned on, and to switch it on, if necessary.

TSB recommends the Federal Aviation Administration and the European Aviation Safety Agency to consider altering the flight manual of the Boeing 737 aircrafts in such a way, that in case of the warning sound indicating a drop in the cabin pressure going off, it becomes possible to check whether air conditioning is turned on, and to switch it on, if necessary.

As a result of accepting the recommendation and by changing the required procedure, the IC believes that emergency descents to be carried out by pilots could be avoided in those cases, when the problem can be quickly and safely solved by switching on the air conditioning.