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Partial engine failure

Thanks for the suggestions Silvaire. I have considered replacing the pump but would prefer to keep the original because 1) the current routing of the fuel lines is quite neat, with no air-traps anywhere. I haven’t managed to find a pump with similar geometry of inlet/outlets. 2) On what is by now a reasonably old aircraft, it’s nice to keep original parts. I’ll talk to my inspector and see whether he’s happy with a home-made nitrile gasket. I am considering a fuel filter between the pump and carb, but with a nitrile gasket would there be any point and could it introduce new problems e.g. fuel stasis and vapour lock?

Achimha: imagine two scenarios. In the first, you go to your doctor and say
‘I want you to tell me if there’s something wrong with me’.
‘What makes you think there might be?’ He asks.
‘Well, you’re the doctor, you should know’, you say, ‘I just want to get checked out.’
‘What for?’
‘For everything!’

In the second scenario you say
‘Doctor, I’m worried there might be something wrong with me. I feel tired all the time, my vision goes blurry on and off and I’m thirsty like you can’t believe’

Which scenario is likely to be the more productive?

Medicine is not aircraft maintenance. Aircraft are more or less understood, but nobody understands the human body. You can’t take it to bits and put it back together again for inspection quite as easily. However I’ve been through the logbooks, and at least 4 inspectors have seen the aircraft since it first had the issue and the whole airframe has been disassembled and the carburetor has been blown out twice. That is, assuming the issues are the same – certainly the gasket didn’t fail overnight. Ideally someone would have spotted it or found the debris but the fact is that they didn’t, but an untrained person did. That is not to say that I’m better than the inspectors – quite the opposite, one of them found several other issues that might have spoiled my day that I would not have noticed. What made the difference is that it’s easier to find something when you have some idea of what you’re looking for. The gasket was hidden quite deep in the pump, and I didn’t catch it the first time round either.

In medicine any test is ascribed a ‘sensitivity’. For example, if someone breaks their neck and you do an X-ray, you have a 90% chance of seeing something wrong. If you do a CT, this approaches 100%. What is the sensitivity of an aircraft inspection? No inspector will catch every fault, but I’d wager the sensitivity becomes much higher if he or she takes a good history first.

True, ideally one or more of the inspectors would have found the issue or suggested that I should disassemble the pump myself. However, speaking generally rather than about my particular case, surely an aircraft seller is morally if not legally responsible for being forthcoming about any issues or incidents in the past. I feel that to suggest that the whole burden rests with the inspector is firstly unrealistic and secondly might suggest to potential sellers that at the point of sale they relinquish their responsibilities.

Last Edited by kwlf at 06 Oct 23:12
EGCW

Nice. I think I would have done exactly the same (for better or worse ) Except one thing. I usually (always, more or less) tune the radio to “information” when flying in G in the mountains, and maybe monitoring the general air to air frequency or some local frequency, or vice versa. My mayday would have been caught within seconds, and within minutes a rescue helicopter would already be on it’s way. Much dependent on terrain and your alt of course, but at 6k there is good coverage. In this case though, I’m not sure it would improve the outcome of the situation. If you knew help was coming, then it would be much easier to decide to land at the first opportunity instead of “pushing on”, which ultimately lead you to an airfield. An airfield is always the best option.

One other thing puzzled me also. You lost your position, don’t you have a GPS?

surely an aircraft seller is morally if not legally responsible for being forthcoming about any issues or incidents in the past.

A good thread is here

This issue will never go away, because why should humans behave any differently when selling a plane compared with selling a car or a house?

That’s why one needs to do a good prebuy, but in this case the fault could not have been picked up by inspection. Only knowledge of the type, and that there are cork gaskets in the fuel system after any filter, would have helped. I would replace that gasket with a rubber one. I think that is the normal solution. The TB20 (and any fuel injected aircraft) has a similar vulnerability via the two gaskets at the two ends of the fuel servo; one is made of high quality rubber and the other is some sort of fibre but is very thin and both are well clamped between two metal surfaces. And it is much easier to block the fuel than to block the air.

Another thing is that one should always replace seals (with new ones) when reassembling. This was the cause of a pretty significant oil leak I had on the exterior of my engine, recently. I re-seated a pushrod shroud tube without replacing the £2 seal at the base of it. With a cork seal, this is especially important. And using cork in the fuel system is crazy because that’s what cork does – little bits come off.

Administrator
Shoreham EGKA, United Kingdom

There are no special laws about selling aircraft as far as I know. An aircraft is just a heap of materials that may or may not function in unison. But, the law is very clear on who is responsible for keeping the aircraft airworthy, that is the owner. Then, to fly the aircraft, the PIC is responsible to check (within his capability) that the aircraft is airworthy and in order for the mission. It couldn’t be simpler.

This is a 50+ ? year old homebuilt with largely unknown history ? The only way to make sure it’s airworthy is to strip it down in all it’s pieces, replace and fix as needed, then put it together again, IMO. I do find it a bit odd you prefer “old looks” over reliability though

It’s been done… Every control surface off, every instrument out and back in again…

It’s not that I value authenticity over reliability, but often I’m not convinced that newer parts for old cars are particularly well made. E.g. Vw cylinder heads have a better reputation than newly manufactured ones; I’ve just bought a carb refurbishment kit which looks as if it was made by an enthusiast in a shed. The gaskets are good but the accelerator pump diaphragm was shoddy. If the problem was clearly with a gasket, why would I replace the whole pump?

EGCW

kwlf wrote:

If the problem was clearly with a gasket, why would I replace the whole pump?

For VW aircraft engines, the norm today seems to be to get rid of the pump altogether, by changing the setup to updraft (the carb below the engine), and using gravity feed. I’m guessing this can be done on the turbulent as well? I have heard even Sauer and Limbach have problems getting reliable fuel pumps (I have no idea if it’s a gasket problem though). The normal setting with an engine driven pump, is also to have an electric backup pump (but this won’t solve the gasket problem either).

I agree there is no need to change the whole pump, I just don’t think the setup itself is the best.

Thanks, that’s interesting. I don’t think it would be entirely simple to install an updraft carb as the magnetos are under the engine, but I can see the advantages of the system.

I suspect the time will come when every aircraft needs an electrical system… At which point an electric pump would become a worthwhile addition.

EGCW

kwlf wrote:

I suspect the time will come when every aircraft needs an electrical system

Sorry to disagree. More and more appliances and accessories can be run from batteries, thanks to the hefty progress in battery technology. I even observe a tendency among gliders to replace FLARM by a proper transponder (but no side-discussions please, flarm has already been discussed to death). There is less reason than ever to have a traditional electrical system in simple planes.

kwlf wrote:

an electric pump would become a worthwhile addition

For your low (or mid?)-winger, yes, perhaps. My own pride and beauty carries fuel in her high wing, gravity does the job of feeding fuel quite nicely. No need to add complexity/potential failure.

EBZH Kiewit, Belgium

Low winger… But with a fuel tank above your legs.

I’m afraid I disagree re. batteries. They’re certainly much better than they used to be, but still very capable of running out. At the very least I would like to have 1 battery to rule them all – radio, pump, headset, gps, transponder…

You asked why I didn’t get my location from my gps..? The answer is that the internal battery only lasts an hour and the external battery switching regulator interferes with the radio. A work in progress… Mid Wales is blissfully easy to navigate provided you keep clear of the Mach loop, but you’re right in that it would have been helpful in the emergency.

Last Edited by kwlf at 07 Oct 12:43
EGCW

kwlf wrote:

At the very least I would like to have 1 battery to rule them all

Technically, that was of course the traditional approach. I am not sure it is still viable with today’s battery technology. And I’d much prefer to have the battery of one ancillary to give out over loosing the one that powers all of them.

But I much appreciate the reference to Master JRRT!

EBZH Kiewit, Belgium
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