DA-42 engine failure

This incident in Germany raises an interesting question about newer aircraft-engine designs. When the pilot(s) of a Diamond Twinstar arrived to find their battery flat, they started both engines using an auxiliary power unit. That’s not an unusual thing to do for a regular piston aircraft, since the alternator or generator will recharge the battery after a few minutes of flight (although it’s better for the battery’s life to trickle charge it); unfortunately, that turns out not to have been a good idea for the Twinstar, which suffered a double-engine failure on takeoff during gear retraction, and had to be belly landed in a field.

The battery was still flat when the pilots started to retract the gear. The gear retraction required enough power that it caused a brief electrical interruption to the Centurion 1.7 diesel engines, and that interruption caused both engines to reset. Now Diamond and Centurion are debating the issue: Centurion points out that operating procedures require at least one engine to be started on battery rather than APU, while Diamond points out that in tests, the engine fails after only a 1.7 ms power interruption, while it should be able to tolerate at least 50 ms.

Magnetos don’t need a battery

I’m sure that the companies will work it out, but in the meantime I’m happy that the 1940s-style technology powering my Warrior is a bit more robust. Once the propeller’s spinning, I could disconnect the battery and throw it out the window, and the engine would still keep running until the tanks are empty — the electricity for the spark plugs comes from a redundant pair of magnetos powered by the engine itself, and do not require a battery or alternator to keep working.

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About David Megginson

Scholar, tech guy, Canuck, open-source/data/information zealot, urban pedestrian, language geek, tea drinker, pater familias, red tory, amateur musician, private pilot.
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5 Responses to DA-42 engine failure

  1. Aviatrix says:

    Yikes, I did not know that about the DA42 systems. When I win the lottery I will have to give serious consideration to not buying one, now. How can you have a machine that you plan to expose to the weather that cannot handle a momentary interruption to electrical power? I have had many electrical problems in airplanes, including a double generator failure in a twin, and a total electrical failure at night, but I’ve never had to question the airplane’s ability to continue generating thrust based on something as fickle as electricity.

  2. Nick Budd says:

    Diesel engines don’t require connection to the electrical system either in order to keep on running, and don’t require mags or spark plugs either. The problem in this case was not with the engine, strictly speaking, but with the automatic engine control system, which is of course electrically-driven. When the engine control system sensed an electical power loss it automatically “reset” itself, which caused the props to feather. In a single with FADEC, you might have the same problem, but you wouldn’t have the feathering effect, of course, and presumably the engine would briefly go to idle and the prop would windmill in the meantime.

  3. david says:

    Thanks for the clarification, Nick — so we should blame FADEC rather than diesel, then, or just a bad FADEC implementation?

  4. Brock says:

    The larger issue is the pilots taking off with a dead battery (or two). Sorry guys, if you don’t know the issues associated with a dead battery and using a APU to start as a solution, you run into things of this nature.

    Very stupid mistake with very sever consequences. I am sure if they ever have a dead battery, they will charge it 100% before taking off. Just like any pilot would do that has more than 2 marbles in their head…

    I am a bit taken back that this likely started with a master switch being left on (purely speculation) and a rush to get back home (gethomeitis). If any pilot does not know how an Alternator works, they are in for a lesson as the aforementioned idiots learned. You must have bias voltage to excite the armature to generate electricity. That means you need electricity to make electricity. The battery would never charge off the alternator alone even if there were enough voltage to make a charge. Generators don’t need voltage to work. Kind of important to know the difference…

    Make sure we all thank the pilots for starting an AD and another legal issue in aviation. It is nice to know the cost of the aircraft will increase thanks to these idiots. God knows it isn’t their fault for the manufacture not taking the idiot factor in every singe detail of construction of an aircraft.

    I’m not sure on the popular opinion, but what idiot would take off with dead batteries in a FADEC power plant? What idiots think a jump start via APU will suffice?

  5. david says:

    Brock: I agree that they shouldn’t have taken off with a dead battery, but it’s still a huge problem if a plane’s engines both shut down because of a very brief electrical interruption — there are a lot of things that can cause an electrical interruption besides taking off with a flat battery. In this case, I think that an AD is probably justified, at least until they figure out a way to make the FADEC system more robust.

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