The pandemic has put a number of older airplanes into expedited retirement this year, pushing down the world’s average fleet age. Still, it wouldn’t be unusual to fly on a commercial plane that’s been used on a daily basis for 20 or even 30-plus years. There’s a common misconception that advanced age might mean the plane is less reliable or even less safe. That’s generally not the case at all, as long as it’s in service with a reputable airline that has good maintenance practices. Most airplanes are designed to fly for at least a couple of decades, and potentially much more (though the 70+ year career of the DC-3 is an outlier). And to truly understand aircraft age you need to look at two factors beyond age: flight hours and pressurization cycles.

Hours and cycles

Most commercial airplanes might last around 30 years in service, but that depends a lot on how they’ve been flown and how many takeoffs and landings they’ve completed. That’s why when evaluating an older airplane the professionals will look at the number of hours flown, and most importantly the number of pressurization cycles. As an aircraft reaches its upper limit for these metrics, metal fatigue can become an issue.

Boeing has said the 747 can handle up to 35,000 pressurization cycles and 165,000 flight hours. A cycle is one pressurization and depressurization – normally one takeoff and landing. The 777-300ER can do 60,000 cycles, but only 160,000 hours. Few aircraft in service today are even close to these limits.

Smaller planes flying shorter flights more often will likely reach end-of-life after fewer hours, but may be designed to handle many more cycles with that in mind. It’s good news for Hawaiian Airlines, for example, that the 717 – its workhorse plane for short inter-island flights – can go through 110,000 pressurization cycles.

It’s possible that any given aircraft could exceed these figures, but these represent the limits up to which they’ve been tested. An airline could in theory perform the necessary inspections to keep a plane flying longer. However it’s often the case that at such advanced age the maintenance and inspection costs begin to outweigh the benefits of keeping a plane.

A few golden oldies

It may be of interest to know that the oldest plane we track on a regular basis on Flightradar24 is this Curtiss Wright Travel Air B-4000, which is a whopping 91 years old. Looking around for old jets, this 53-year old DC-9 is among the oldest still flying regularly – though this ex-TWA plane was converted to carry cargo and no longer shuttles passengers around. Most of the oldest planes you can still fly on as a passenger will have been built in the 1970s, though with the situation as it is lately there’s no telling how many of these will remain active once flying picks back up again. One particularly appealing and ancient plane is this 747-200 flying for Saha Airlines in Iran, which is now 42 years old.

Age ain’t nothing but a number

When you find yourself flying on a brand new airplane it’s usually pretty obvious. Everything looks clean and fresh, the seats feature the latest designs and technology, and then there’s that new plane smell. But these things can be deceiving. I’ve seen plenty of instances where an older aircraft gets a refreshed interior and passengers remark at the “new plane” on boarding, for instance on one of United Airlines 767-300s fitted with the latest Polaris business class and premium economy seats. Those planes look great inside, but most are over 20 years old. And in terms of the airframe they have plenty of potential life left in them (though whether they get pulled from service for economic reasons is another story.)

The relatively aged 747-400s at British Airways that are now being sent off for retirement were initially slated to fly for some years to come. Yes they are old, but a big part of pulling them from service early is that they’re configured with too many premium seats to be profitable.

The reality is that over the course of a given aircraft’s life, it will be more or less taken apart and rebuilt several times in periodic “heavy” maintenance checks. During these checks just about every piece of the interior is removed, checked and replaced if necessary. Engines will also be overhauled regularly. The airframe itself is the only piece that remains more or less the same – and it’s a testament to the design of modern commercial planes that they can keep flying safely for so long.