For anyone who doesn’t subscribe to the AOPA newsletter, the latest one contains a warning against excess preventative maintenance. The “Waddington Effect” was discovered during WW2 by a developmental biologist, C H Waddington, working for the RAF’s Coastal Command, who observed that their Sunderlands were more likely to break down in the period immediately after scheduled maintenance. Mike Busch writes a typically thought-provoking article about it.
What chance EASA would remove the requirement for 50-hour checks, if empirical evidence suggested it decreased safety?
What chance EASA would remove the requirement for 50-hour checks, if empirical evidence suggested it decreased safety?
None, because there is no current “empirical evidence” supporting this issue. The statistics generated by Waddington and his team were derived from wartime field maintenance 70 (!) years ago. Maintenance performed by poorly trained soldiers on the most maintenance-unfriendly aircraft under adverse conditions who had to drop their tools every half hour and run to the next air raid shelter. Absolutely meaningless.
But I would suggest that the author of this article exposes his theories to the airline industry. There he will be met by the very happy faces of some low-cost carrier CEOs if he can give them a reason to do away with all the useless and costly scheduled maintenance performed on their aeroplanes…
What chance EASA would remove the requirement for 50-hour checks, if empirical evidence suggested it decreased safety?
It’s not EASA mandating that check but the manufacturer. At least for the aircraft I’ve maintained, the 50h check is a very simple operation. For an oil change, said Mike Busch is of the opinion that 50h is too long. The remainder is mostly checking, cleaning and gapping the spark plugs and that is absolutely necessary to do every 50h when running on avgas. Due to the lead deposits, the spark plugs need cleaning. Apart from those two jobs, there isn’t much else to do other than visually inspect a few things. On my TR182, a 50h check takes me 2-3h alone.
The oil certainly needs doing, and yes 25hrs is better than 50 and this is generally evident in the oil analysis.
The spark plugs I am less sure about. If you use iridium (fine wire) plugs there is no perceptible wear after 1000hrs and probably not after 2000hrs. The bottom plugs always have lead deposits, the upper plugs never have lead deposits (IME) so I am not sure that the ritual of cleaning out the lead deposits is actually required. The insulator inspection is good to do but – for the shorter plugs anyway, maybe not the long reach SR22 plugs – there might not be statistical support for inspecting them so often.
It is certainly true for me that significant defects were found only on the first flight after a service, but that just speaks for the people doing the service. Since I started doing my “50hr” checks myself in 2005, and the Annual myself in 2011 (in all cases with an A&P/IA colleague) I never had a service related issue. And frankly anybody who gets an issue after a 50hr check must be using a complete load of orangutans.
“The oil certainly needs doing, and yes 25hrs is better than 50 and this is generally evident in the oil analysis.”
But is that the case with aircraft that run on unleaded fuel? I know of a C150 that racks up 50 hours a fortnight over the summer months and that runs on ul91 and I have to say with the naked eye the oil appears alot cleaner. It also doesn’t have any plug fouling problems.
Also there is a commercial IO540 operater who have a TBO of 3000 hours on their engines. I’ve also heard that they don’t do 50 hour checks but only do 100 hours.
Cape Air in the states only do 100 hour check and they must be the biggest user of piston aircraft about.
I am certain you will have cleaner oil if on 91UL. Whether this equals the same wear protection, I don’t know.
I have rarely gone to or over 50hrs but when I did, I did let significantly increased (pro rated basis) metals in the oil analysis. OTOH that increase just means more wear; it doesn’t mean the engine will be out of spec, let alone unairworthy according to the rather crude criteria (e.g. 1 qt of oil per hour – no kidding!) at 2k or even 3k hrs.
I think water, and the resulting corrosive products, are the biggest enemy, so an operator flying daily, in Arizona, is going to have an easier time.
Also there is a commercial IO540 operater who have a TBO of 3000 hours on their engines. I’ve also heard that they don’t do 50 hour checks but only do 100 hours.
Commercial operators do their maintenance as per CAME, which is worked out between the maintenance organisation (CAMO) and the operator observing the input from the manufacturer and individually approved by the relevant authority. So what one operator does is not necessarily what other operators will do. When I was flying the C404 and C421 (both with GTSIO540 engines) commercially some years ago we had to do 50hour inspections. And that was a good thing because these aircraft were operated close to the red lines most of the time (express freight with slow aircraft which is a contradiction in itself…).
Under EASA you have to do 50 hour checks, but under FAA / N reg rules its just 100 hours right?
FAA 100hrs are only if the aircraft is used for hire.
For the private owner, a.k.a. Part 91, it’s just the annual.
The Part 91 100hr check is only if you carry paying passengers, or train others in your plane.
It is not required if you just rent it out.
Reference: FAR 91.409.
50hr checks are not mandatory under Part 91 (for SEPs, generally) but are required by the usual engine manufacturers. However, with say a G-reg if you go over 50hrs then the flight is illegal before it got off the ground (thus, arguably, no insurance) unless you apply for an extension and get it, while with say an N-reg it is not illegal to go over the 50hrs.
It is dumb to go over 50hrs regularly, but it isn’t going to trash the engine for a little while. I recall reading one accident report recently where, reading between the lines, the engine had not seen any servicing for many years. Maybe the oil was just topped up. A friend of mine ran a Renault like that, for about 15 years. I will see if I can find the report.
