Aircraft structural analysis programs are used to investigate the characteristics of an aircraft’s structure in its normal operating environment, typically to establish if their in-service life can be extended or to ensure flight safety. These programs are especially important when an aircraft's role changes as the stresses and strains encountered in new operational environments or flight envelopes may now be significantly different than initially anticipated.
Monitoring the fatigue of individual aircraft is necessary to quantify the loads experienced by each aircraft as these can show great variation. Once the total fatigue experienced by the airframe can be determined, an informed decision can be made regarding safety and maintenance. Initial design calculations and predicted flight fatigue can be compared with the actual fatigue to ensure that the aircraft can be flown safely, and with adequate flight clearance for the airframe. It is the aircraft’s use that compromises fatigue life, not so much the number of hours in use.
For aircraft the fatigue life will depend on several factor including
- Flight role – e.g. Fighter, Trainer, Recon, Carrier etc.
- Number of take-offs and landings
- Payload weight and distribution
- Environment – hot, cold, wet, dry, salty, quality of runway
- Different pilot flying practices
- Servicing intervals