Lifetimes of jet aircrafts and their engines

[Astronuc]

I found this article today.
Jalopnik - Here's How Often Airlines Replace the Jet Engines on Passenger Planes

The rated lifespan of a plane can vary widely by fuselage size and composition. Short-range narrowbody aircraft, like the Airbus A320, can last almost 50,000 flight cycles. According to Simple Flying, long-range widebody planes have a life that can range between 25,000 and 45,000 cycles. For example, the iconic Boeing 747 has a manufacturer-estimated lifespan of 35,000 flight cycles. The composite-structured Boeing 787 Dreamliner can endure 44,000 flight cycles, 9,000 more than the jumbo jet.

https://jalopnik.com/how-airlines-decide-to-replace-jet-engine-boeing-airbus-1850275010

The plane’s jet engines will not last the aircraft’s entire lifespan and will have to be replaced at some point. Engines are overhauled two or three times before being taken out of service. For narrowbody engines, this usually happens after 12,000 flight cycles. The number of cycles is cut down to 8,000 until the second overhaul and then halved to 4,000 for the third. However, airlines may simply replace the engines instead of spending millions on further rebuilds.

 

[Flyboy]

It makes sense if you think about it, though. You have a lot of transient loads, both mechanical and thermal, during startup and shutdown alone, let alone the takeoff. Once you get steady state at cruise, they're not nearly as heavily stressed and can run for long stretches of time, which is why most airliner engines are monitored by cycles as well as run time. Accessories on the gearbox can be time limited instead of cycle limited, but even then, most of it is "on condition".

That said, I am somewhat familiar with the smaller engines used on business jets and those both have shorter intervals between overhauls and can undergo more overhauls, iirc. The JT-15D-5s that I worked with were ~1800 flight hours between "hot section" (combustion and power turbine sections) overhauls, which came to about 2 years or so for the planes I worked with. Total overhauls were every other hot section. I don't know what the life limit on the engine was, but it was quite a while, probably comparable to the life limit of the airframe at 36k cycles for the Hawker 400s I worked with.

That said, engine swaps are actually pretty quick once you do a couple of them. We got it down to ~2-3 days for a dual engine swap on the 400s, and that was doing one at a time because we only had one hoist to install/remove engines. Single swaps were basically unheard of outside of a FOD incident.