There are three ways of ascertaining the life of an aircraft based on about a dozen factors like its frame construction, weight, engine strength, average flight time, etc. The first unit of measuring longevity of an aircraft is year. A passenger aircraft like Boeing-747 or Airbus 300 is normally considered “aged” after 20 years of service. However, it is inadequate to ascertain the age of an airplane in years alone. It is also important to take into account the number of take-offs and landings by an aircraft within a span of time, which is called usage cycle.
At the time of landing an aircraft endures a mild collision vertically, whereas during take-off the entire frame endures a horizontal pull. Aircraft’s metal then “tires” just like human muscles after physical hard work, and gradually becomes weak. To talk in the language of engineering, an aircraft experiences metal fatigue. The most memorable example for this is of Boeing-737 of Aloha Airlines in Hawaii. Flying between various islands this plane took off from the runway for a similar flight on April 1988, and when it was at the height of thousands of feet all of a sudden its roof went off. One air-hostess and a passenger were thrown out with the wind, while the other passengers had their seat-belts on, hence they remained safe with minor injuries. Eventually the plane landed on the airport, but in the below picture you can see the condition it is in. After this accident Boeing declared the life of Boeing-737 to be 75000 cycles. It means once the aircraft completes 75000 take-offs and landings its life is over.
|Aloha Airlines’ Boeing-737 Accident|
The third unit of measuring an aircraft’s life is hours of flight. At the latitude of 32000-33000 feet the air temperature is about minus 48° Celsius. Plane’s metal is contracted at that low temperature. After beginning to land, within 15 minutes as the plane hits the ground the air temperature is much higher, possibly around 30° Celsius. Such a difference in temperature within 15 minutes is no small matter. As a result of this an aircraft experiences another kind of metal fatigue which diminishes its strength. By this measure, the life of Boeing-737 is 51000 hours of flight. Whereas the life of the supersonic Concord is 45000 hours of flight. For more information about different planes refer to the table below. As shown in the table there are three parameters of longevity. A take-off and landing equals one cycle. Boeing-747 (Jumbo Jet) is meant for International travel, hence it does fewer take-offs and landings and has higher hours of flight compared to the planes used for domestic flights.