Anyone here maintain planes?

[rob justice]

I was sent on a training course - load of crap but a week off work so it wasn't too bad.
Bloke who took the course baised his findings on the aviation industry in relation - it was all about mechanical failings.
Bloke said something that woke me up big style - Most (If not all) systems on planes now are designed to run to fail!!!
I always thought air frames were designed to handle certain amount of take off's and landings whilst engines were monitored throughout their life and after again after a certain amount of hours - were changed full stop.
I would think nothing on a plane would be designed to run to fail but kept my mouth shut rather than look the fool.
Any comments/thoughts?
Regards
Rob Justice

[Tim Hancock]

In general aviation, engines typically have a recommended TBO (time before overhaul) time. This time (varies, but most are 1500-2000 hrs) is the "recommended" time that the engine should go before needing a major overhaul. Most engines if they ever get this far, are getting pretty tired by this time. Most airframes (general aviation types) do not have any accumulated time factors at least when they were built. That said, the when the FAA finds that an occasional item or part on a certain
type plane is faulty, an AD (Airworthiness Directive)is issued that may include time restrictions on some parts.

On general aviation aircraft, annual inspections must be completed by mechanics with an IA rating (inspection authorization). At this time, applicable AD's for the aircraft being inspected are checked and complied with where needed.

[rob justice]

Speaking to a bloke who knows more on the subject - His thoughts on aircraft parts running to fail - off the top of his head 'interior lighting'!!!!!
The amount of maintaining and trace-ability in avaition is almost unique.

[Joeaksa]

Rob,

Jet engines these days in many cases have no overhaul time limit. They are "on condition" which means that you run them until they run out of cycles on rotating components or "a condition" presents itself making it need repair.

Like this:







What Tim said above is correct. What has changed in the past 60 years with regards to aircraft is the lubrication. During WW2 an engine might last as little as 25-50 hours before needing overhaul, but then they were run hard. Oils and maintenance have taken this to where the same engine today would get at least 1000 hours before needing overhaul.

You also have airframe limits. I used to fly a old Vickers Viscount. They were 30+ years old and British Aerospace put a limit on the planes. After 15000 cycles (take off and landing is one cycle) they could not be pressurized above 3 psi in the cabin. This meant that we could not fly above 18,000 feet or so, which really limited the range, caused the fuel burns to go out of sight and doomed the planes.

Hope this helps...

Joe A

[beepbeep]

I know wery little about airplanes but as far as I know, comercial airplanes are limited in two ways:

They have A,B and C-check issued every X-amount of hours or cycles where A represents light inspection and C total overhaul where everything is reset to almost-new.

Then there is final max amount of cycles issued by manufacturer (often too high to be touched in service).

With other words, you can have perfectly healthy 30 yr old intercontinental 747 with 70k hours but few cycles (due to long trips) or crotchety (even "cabbed") 737 with few hours but exorbitant amount of cycles beacuse of short island hops.

Sometimes, perfectly functional planes are scrapped beacuse they require costly C-checks and/or are gas-guzzlers.