What percentage of a commercial aircraft's service life is spent airbourne?

Answer 1

All of it! A commercial aircraft is considered "In Service" when it is in flight. Time spent sitting on the ground is usually not counted for service life for airframe or for most components.

Of course, there are exceptions to every rule... small piston engined airplanes sometimes have an hour-meter connected to the engine's oil pressure gauge, so that the meter records the total time the engine is running instead of actual flight time. Most larger aircraft have a "squat switch" connected to the landing gear, so the hour-meter only records time spent with the wheels off the ground.

Answer 2

You are talking about its time as part of the active fleet of airplanes for a given airline... and I think both of the above posters know that too... that varries alot based on aircraft type however, the 747 for example will spend about 5 hours in a layover for every flight, some of a 747's flights are over 12 hrs, therefore it spends well over half its day in the air... it has to "sit out" for a long time though when maintanace comes due... the regional airplanes spend more time on the ground because they go through more cycles per day... they may fly 6-8 flights a day with the same plane and checks on a small plane are obviously much quicker than a large one...

Answer 3

I would think its "service life" is when airborne.

Military cargo aircraft use a life in hours, usually pertaining to the center wing box.