Airframes have a limited lifetime, partially defined by takeoffs and landings (and pressurization cycles). Cargo planes experience fewer cycles than passenger airlines since cargo carriers' aircraft usually only make a one or two flights a day, whereas passenger aircraft a flown back to back as frequently as possible. Historically, cargo carriers would buy used aircraft and convert them, but that's changing.

This particular aircraft was acquired by UPS in 2006 and converted for cargo missions. It was originally delivered as a passenger aircraft to Thai Airways International in 1991. [1] I actually saw this exact aircraft at RDU International in August of this year and took a photo, since tri-engine aircraft in general are not very common these days.

[1]: https://www.flightradar24.com/blog/flight-tracking-news/majo...

The gist is correct, but the subtleties are hiding in the details.

Wide-body (long-haul) airplanes are generally limited by flying hours since they rarely reach their maximum allowed flight cycles.

In contrast, wide-body cargo planes typically fly shorter legs compared to when they are used as passenger carriers. And as a result, they are much more likely to hit their critical cycle limit.

Thanks for the explanation. I'll see if I can find some data on cargo planes.