Flying hours versus Fatigue Index
 

I might be asking the question in the wrong place here, but standing at Coningsby waiting for some other movements after the Lanc departed.

Someone got a tad miffed over the discussion about the above for Tornados, I stated that airframes are retired after the FI calculations are taken into account, and not the number of hours flown...

Am I correct or not? :eek:

I certainly sent one of the spotters packing:E

V1

Flying hours versus Fatigue Index
 

Basically yes. 5000 hours straight and level at 20000' is vastly different to 5000 hours bumping around at low level flying down valleys.
Sorties are assigned codes which will signify an approximate level of fatigue for that mission. It is these codes and G meter readings, amongst other things, that will ultimately see a jet consigned to the scrap heap when the time is right.
Different jets obviously have very different airframe lives and this will be related to their construction, role and several other factors.
I have simplified things markedly but you get the idea.
BV

The total life of an aircraft is usually based on a combination of fatigue life factors. There is a design requirement for an aircraft to reach a certain number of hours or cycles (the design service goal) and that is partly based on the mission mix the aircraft is assumed to carry out throughout it's life. So maybe 70% is cruise profiles, 20% is low level profiles and 10% is dogfighting. If the more ardous profiles exceed their assumed percentage then the total life in terms of hours (or cycles) can come down from the design estimate. Throw in to the mix that some parts are replaced after a certain number of cycles and at different times, or if an envelope is exceeded and you generally become limited by a part of the structure you can't change eg a wing pivot or a wing skin around a landing gear bay. There's lots of work done to extend service goals if the demand is there, and the manufacturers can go to great length to replace parts that are not meeting the design service goal.