Abnormal and Emergency: Pressurization Failure and Emergency Descent
You are pilot-in-command of a twin-engine turboprop (MTOW 5,700 kg) at FL250 en route from Brunei to Singapore. The cabin altitude warning sounds, and you see the cabin altitude climbing through 10,000 ft. You and your co-pilot are on oxygen masks. The passenger oxygen masks have deployed. You must decide whether to perform an emergency descent and what communications are required.
1. What is the correct emergency descent procedure and what ATC communication is required?
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You must immediately don oxygen masks, establish communication with ATC, and initiate an emergency descent. The standard procedure: announce 'Mayday, Mayday, Mayday, [callsign], emergency descent, FL250 to 10,000 ft, [position].' Then set power to idle, extend speed brakes, and descend at maximum rate or as appropriate. Turn off the autopilot if needed, and maintain directional control. You must descend to 10,000 ft or the minimum safe altitude, whichever is higher. ATC will clear the airspace. You should also consider the terrain; if terrain is a factor, you may need to level off at a higher altitude. The key is to act quickly; hypoxia can impair judgment. After descending, assess the situation and decide whether to divert or continue. If the cabin altitude cannot be controlled, you must land as soon as possible.
2. What are the considerations for diverting to the nearest suitable airport?
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You must consider the nearest suitable airport with adequate weather, runway length, and emergency services. If the pressurization failure is uncontrollable, you must land as soon as practicable. Check the weather at Brunei and other nearby airports; if Brunei is suitable, return. Consider fuel: you may need to dump fuel if above maximum landing weight, but in an emergency, you can land overweight if necessary. Communicate with ATC to request priority and emergency services. After landing, evacuate if there is a fire risk, but in this case, a normal landing may be sufficient. The key is to prioritize safety and land as soon as possible.