 a descent during air travel is any portion where an aircraft decreases altitude, and is the opposite of an ascent or climb. descents are part of normal procedures, but also occur during emergencies, such as rapid or explosive decompression, forcing an emergency descent to below  and preferably below , respectively the maximum temporary safe altitude for an unpressurized aircraft and the maximum safe altitude for extended duration. the table lists above 10,000 to be limited to six minutes.see loss of pressurization: the maximum sustained cabin pressure altitude is . to counter potential passenger and crew decompression sickness, hypoxia, edemas, and rewarm the cabin, pilots descend to minimum safe altitude which avoids terrain. an example of explosive decompression is aloha airlines flight 243. involuntary descent might occur from a decrease in power, decreased lift (wing icing), an increase in drag, or flying in an air mass moving downward, such as a terrain induced downdraft, near a thunderstorm, in a downburst, or microburst. ==normal descents== intentional descents might be undertaken to land, avoid other air traffic or poor flight conditions (turbulence, icing conditions, or bad weather), clouds (particularly under visual flight rules), to see something lower, to enter warmer air (see adiabatic lapse rate), or to take advantage of wind direction of a different altitude, particularly with balloons. normal descents take place at a constant airspeed and constant angle of descent (3 degree final approach at most airports). the pilot controls the angle of descent by varying engine power and pitch angle (lowering the nose) to keep the airspeed constant. unpowered descents (such as engine failure) are steeper than powered descents 
Flight_phases