Originally Posted by
adrian1980uk
... I just thought that the 747-400s have probably been running around 18 hours a day (I guess) ...
It is amazing to think about it, but I don't think it's quite that many hours if you allow for downtime for maintenance etc.
Looking on G-INFO, for example, the recorded hours for G-BNLI are 106,406 as at 31 December 2012. She was registered on 19 April 1990, so that's about 22½ years. That makes it just under 13 hours per day.
Probably a higher average time for the young aircraft that have not been into heavy maintenance. For example, the baby of the fleet G-STBF is recorded as 4,591 hours as at 31 December 2012. Registered on 21 February 2012, that makes it an average of just over 15 hours per day.