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.