Electric fuel pump failure - how big is the risk?
 

So there I was before engine start, but when I turned on the electric fuel pump, the amber fuel pressure warning light remained lit. I turned the electric pump off and on again, no change, the light remained. I could hear the pump working behind me, but it was "missing a beat" sometimes, wasn't as regular as it used to be.

Suspecting this might be a partial failure, membrane leakage for example, I gave the starter a try and the engine started up normally, with the fuel pressure warning light going off.

Realistically, how big is the risk flying such an airplane? Is there any known incident, where the failure of both the main and the electric fuel pump resulted in a complete engine failure and a forced landing?

We use the electric pump during take off and landing. And of course, in case the warning light comes on due to failure of the main pump operated by the engine itself.

No electric pump fitted to my aircraft, just the mechanical (and a wobble pump).

I have had an engine driven fuel pump fail twice. Once on a Curtis Wright 1820 Radial and the other time on a Lycoming O 320. Both times the engine picked up as soon as I turned the electric pump on. In the case of the Lycoming no operative electric pump would have resulted in a crash landing in inhospitable terrain, because of the pump I made an uneventful diversion to the nearest airport.

Flight with an inoperable fuel pump is both illegal as the aircraft certificate of airworthiness would not be in effect and IMHO, stupid as the electric fuel pump is the redundancy for a single point of failure.

Would you fly the airplane if only one magneto was working ?

Probably not, because the failure of the remaining ignition circuit would certainly result in an immediate loss of engine power.

On a related note however there are quite many simple aircraft in low-cost category (ultralights, trikes), which fly with non-certified engines, or even with automotive engines having a single ignition circuit. Naturally, as a mitigation, they have to fly overterrain with emergency landing options avaiable at all times, this is part of the POH, placarded etc.

I guess the keyword is "where reasonable". With non-certified engines, it's plain illegal to fly over terrain without emergency options, because an engine failure is a non-event by their standards.

With a certified single engine, you can do that if there no other ways, and if I crash due to an engine failure in-flight, the engine manufacturer and the maintenance guys will be investigated too. Not that it makes any of the pain lower, but this puts pressure on both to do a good job, use quality materials, tools, testing equipment etc.

And would that invalidate the insurance? It would certainly look very silly on the claim form & AAIB report.

Why would you claim or confess that? Unless the failure was already recorded in the aircraft logbook prior to the flight, it's difficult to prove that the pilot took off with a pre-existing malfunction.

Technically, this malfunction can be detected only before engine start, so if your electric pump fails on takeoff, you won't notice it and will happily cruise around in mountains, rocky deserts, and the oceans without knowing that the assumed redundancy doesn't protect the engine anymore.

I had an electric fuel pump failure at a hill-top strip, with high winds forecast. I flew the aircraft to our homebase, where it was not flown again until it was repaired. (20 minute flight.)
I have twice had post-maintenance problems with the mechanical pump, detected on climb-out. In both cases, although the engine worked normally with the electric pump on, I immediately returned, and did not fly until problem was fixed. In one case, fuel was pouring out of the pump.

I've twice refused to fly hired club aircraft with U/S electric fuel pumps. One one occasion, I was told afterwards by an engineer that it'd been like that for a week, that I was only the third person to notice and was the only one not to agree to fly it. :ugh:

I remember one aircraft where both fuel gauges were permanently stuck on 3/4 full for at least a month. On one preflight just after a student had just landed it I could see no visible fuel whatever in the tanks. Another time the wing bolts on a PA-38 were so loose you could move the wingtip several inches from side to side.

I'd booked an aircraft for a 2hr flight to Europe for a weekend away and it was handed over with an extremely soft tyre and a bad misfire on the left mag. After complaining, I was told there was a slow puncture in the tyre & that the engine had been oiling plugs all week. They offered me a spare set of plugs, a plug spanner & a footpump. I turned around and drove home.

Always check everything before you fly, particularly on something you've just rented.

The manufacturer installed the electrical pump to ensure sufficient fuel pressure for full power. It may well be to allow for mechanical pump failure or it may be required on every flight. But a broken pump means a grounded aircraft, whether or not the thing starts.

PM