LIFESPAN OF AN AIRCRAFT

Bhoja air crash at Islamabad had generated widespread comment on the age of the aircraft being above 20 yrs old and still being engaged in service.Without prejudice to the impending investigation, let's look at what governs the airworthiness of an aircraft and especially when aging.

Aircraft lifespan is usually dependant on takeoff and landings. One cycle constitutes a takeoff and a landing. Each time a cycle is undergone, the aircraft is subject to fatigue,especially on short hauls wherein the number of cycles increase.Aircrafts are subject to long haul operation wherein less number of pressurisation cycles happen, and the aircraft have been known to stretch to over 20 years. Classic example is that of B747 itself.

Cycles are a better way of measuring wear and tear on the aircraft. Engines go by number of hours performed and maintenance program's regularly ensure that parts are replaced not only because of wear and tear, but because of life- limited replacement.Maintenance program's are there to prevent any catastrophic failures by ensuring that components are changed  regularly due to life-limited requirement in addition to replacements due to fatigue, corrosion, etc. Hence, judging the aircraft solely on its age is not truly representative of the actual airworthiness of the aircraft.