I know that aircraft are pretty well built and maintained, but I am certain that while flying these aircraft also suffer from some or the other mechanical issues. I believe redundancy plays a huge part in keeping these aircraft in air, but how many times are the passengers really oblivious to the problems? What are some of the most common problems that pilots are used to?

  • $\begingroup$ What do you mean by "civilian"? General aviation (also known as GA) (e.g. the DR-400 can transport 3 passengers + 1 pilot)? airliners? (note that military uses aircraft developed from airliners such as the VC-25 or the A330MRTT) $\endgroup$
    – Manu H
    Aug 25, 2020 at 17:30
  • $\begingroup$ Civilian meaning ferrying passengers on commercial aircraft for which they are paying a price. American airlines, United etc. $\endgroup$
    – rvphx
    Aug 25, 2020 at 19:09
  • $\begingroup$ thus you mean airliners. Also note that some airliner are really small one. You should precise inside the question aircrafts concerned (e.g. those certified to carry at least 19 passengers, jet-airliners,...) $\endgroup$
    – Manu H
    Aug 25, 2020 at 19:25
  • 3
    $\begingroup$ @Manu H come on, you're being a bit over the top. It was very clear what he meant, you can't expect people with a passing interest in aviation to specify 19 seats or above... $\endgroup$
    – Ben
    Aug 25, 2020 at 21:36
  • $\begingroup$ @Ben I agree, when posting a question you don't necessarily know the best way to restrict it as you don't think about all restriction (e.g. aircraft that are not airliners nor military can transport passengers and can thus be concerned by this question). Comments are also here to help precise questions, as explained in the help center $\endgroup$
    – Manu H
    Aug 26, 2020 at 5:20

2 Answers 2


I don't think you'll find a definitive answer because most will be just considered routine items, but if you're including non-safety-critical items then I imagine the answer is "lots". Passenger aircraft are huge, complex, mechanical devices with many many parts. It is accepted and expected that some of these things will occasionally fail.

Most of these can fail gracefully without impacting the flight in any way beyond a note in the tech log. Not only that, but lots of things can be known to have failed but still allow the flight to go ahead as normal.

You may wish to explore the idea of Minimum Equipment Lists. These provide exhaustive lists of items which can fail and flights can still be dispatched as normal. Note this isn't the same as an in-flight failure occurring and continuing to the destination - items in these lists can be failed before you even take off.

For example, here's one for the Airbus A320: https://fsims.faa.gov/wdocs/mmel/a-320%20r21.pdf

Everything listed in that document can be failed in some way, but a flight still operate as normal (with exceptions, as per the remarks column)

For example, and to highlight the level of detail, an Airbus A380 does not need to be grounded because the "PA In Use" notification light doesn't work.

  • 1
    $\begingroup$ Agreed, Just about every flight will end with something on the aircraft needing to be fixed, or deferred to be fixed at a later time. $\endgroup$ Aug 25, 2020 at 16:04
  • 1
    $\begingroup$ I wouldn't be surprised to learn that no flight has ever taken off without at least one thing not working in some fashion or other. $\endgroup$ Aug 25, 2020 at 16:22
  • $\begingroup$ related: What, exactly is “on the MEL”? $\endgroup$
    – Manu H
    Aug 25, 2020 at 19:27
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    $\begingroup$ Back in the 1990s on 747-100/200 aircraft, the f.e. would be first into the cockpit and would review the maintenance log. When the captain arrived, the f.e. would brief him on the maintenance status. Occasionally the f.e. would say that we had a "clean airplane," meaning that there were no outstanding deferred items. Usually, though, there was at least one, more often than not more than one. Deferred items that were in the cockpit or controlled from the cockpit, would have a bright yellow sticker next to the item. Sometimes it was a colorful cockpit. $\endgroup$
    – Terry
    Aug 25, 2020 at 23:52
  • $\begingroup$ @JörgWMittag - like Terry said, occasionally it does happen on airliners. It's even more rare in (US) Military Aviation - where it's called a black-initial or black-letter, and it usually makes a news release when it does like this one $\endgroup$
    – SSumner
    Aug 26, 2020 at 11:13

It used to be normal for the airliners of the day to have multiple non-critical fault alarms active at takeoff. Airlines tended to take the view that if an alarm is non-critical then there is no problem, no need to hold the aircraft back. Pilots complained that there were often so many that spotting a critical warning among them could become a problem. Pilots also often disabled them (especially audible bleepers, buzzers and such) to reduce the level of distractions. Keeping the level to manageable proportions is an important part of modern flight deck instrumentation design; the fault indicattions are still there, but not intrusive. Different airlines tolerate different levels of fault indication.

I was once a passenger in a venerable Dakota, still being operated by a commercial airline. Several rows of rivets were missing from the trailing edge of one elevator. Most had been replaced by twisted wire, but some holes were just left. It had evidently passed inspection nonetheless. Most passengers never noticed, and the trip was uneventful.

The general approach to passenger information is often, as they say, "what the eye don't see, the heart don't grieve over".

  • $\begingroup$ To say "multiple non-critical warnings active at takeoff" is incorrect. A writeup isn't a warning; if I have anything on the Master Caution active, we won't start the takeoff until it has been addressed. This answer far overstates how much may be wrong with a modern airliner. On the other hand, they're incredibly reliable machines. $\endgroup$
    – Ralph J
    Aug 26, 2020 at 16:19
  • $\begingroup$ @RalphJ Can you explain why a fuss gets made periodically - or certainly used to be - over the confusion to pilots caused by excessive numbers of such devices being active? $\endgroup$ Aug 26, 2020 at 16:25
  • $\begingroup$ Can you reference where such fuss is made? Because I haven't seen much in many, many years. Airliners are complex, so there is necessarily many indicators in the cockpit, but all warnings, cautions and alerts are prioritized and colour-coded exactly so that it is easy to tell what is most important at any given moment. And have been for at least 40 years. $\endgroup$
    – Jan Hudec
    Aug 28, 2020 at 20:42
  • $\begingroup$ On a side note, a non-critical warning is an oxymoron, because warning means something that needs immediate attention. The other categories are cautions, alerts and memos. $\endgroup$
    – Jan Hudec
    Aug 28, 2020 at 20:43
  • $\begingroup$ @JanHudec Sounds like the issue has been sorted on modern types then, I lost touch while the "we really need to do something about this" voices were still strong. Many older cacophanous types are still flying with lesser airlines (especially overseas), maybe pilots here are lucky enough to be with the better ones. No refs while the Flight archive is down, sorry. $\endgroup$ Aug 28, 2020 at 21:02

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