About Pressurization and Air Conditioning System
Basic concepts (more are given during analysis):
Air conditioning system and pressurization system can be taken as one system. Pressurization system takes bleed air from the engine to pressurize the cabin. When the airplane is at high altitude with thin air outside, the cabin is pressurized by adjusting the outflow valve in the rear fuselage to keep a comfortable pressure level for people on board. The Air conditioning system conditions bleed air to a comfortable temperature level. Problems with the air conditioning system does not necessarily affect pressurization in the cabin, whereas when pressurization goes wrong, air conditioning system would always have problems. Reported certain air conditioning system problem does not necessarily imply depressurization, unless the pressurization system failed before the air conditioning system and, very unlikely, this was not noticed by the pilots.
Since depressurization is a nuisance case requiring immediate action, it is considered even more dangerous than engine failures. In some airlines, pilots are required to keep an eye on pressurization system during entire flight, especially on those with previous malfunction report. Pressurization problem is noticed by instrument readings on pressurization panel in cockpit. When cabin pressure reaches 10,000 feet, there is a horn warning pilots of the potential danger. Pilots must take actions based on memory items on checklist.
1. There are procedures and checklists that help pilots deal with most of the technical problems on the airplane. Checklists are composed of memory items and read-and-do items by its emergency level. Situations on the plane requiring immediate action without going to the hard copy checklist are made to be memory items. This kind of situations is indicated by aural, visual, or textile warning which is very unlikely being not noticed. Cabin Depressurization is one of these situations that triggers alert and immediate action.
This specific procedure, during training, is included in both fix base and flight simulator tests which is supposed to be error-free, though not necessarily solve the depressurization problem itself, but surely the items in the procedure have to be carried out ended with emergency descend to a safe altitude, mostly 10,000 feet.
2. According to the fighter jets reports, the airplane was at 34,000 feet, which corresponds to an outside temperature of about -50oC;