On 2007-04-24 14:47:11 -0700, "Friedrich Ostertag"
said:

Neil Gould wrote:
Recently, Friedrich Ostertag
posted:

Karl-Heinz Kuenzel wrote:
Hi.

Here in Germany we had an accident with a brand new DA 42 in Speyer
(EDRY) on 3-4-07 during take off.

It seems, that the battery was down and both engine were started
with remote power.
After take off when retracting the gear, the props feathered and
both engines stopped.

You can read about that accident in German (sorry) in
www.pilotundflugzeug.de

First hearing about that accident and the background, I could not
believe it.

I don't even know where to start. How can an aircraft, that depends
on electrical power for the operation of it's engines, be airworthy
without fully redundant electrical systems? While in this particular
case the pilot might have noticed the problem, had he meticuously
follow procedures and started the second engine at the plane's own
power, it is quite easy to find failure modes that would go unnoticed
inflight, yet cause double engine failure at the instant the gear is
lowered on final. Lead batteries are known to occasionally go flat
suddenly, once the buildup of oxide makes contact between the lead
elements. Happened to me in the car once. The engine (a diesel with
mechanical injection pump) ran happily without me even noticing the
failure until I shut it down. When I turned the power back on again,
not even the lights in the dashboard would light up, it was
completely and utterly dead.

I would never have thought that they cut corners like that at
Diamond. I Hope this will not create a lot of mistrust in
aerodiesels, as it is not a diesel issue. I guess you could call it a
FADEC issue if you wanted, however it really is an issue of
redundancy of essential systems, and easily solveable as such.

I have a somewhat different take on this event. It appears to me that
the pilot didn't sufficiently understand his aircraft or the
implications of the symptoms he observed. Knowing that there was
insufficient power to start the engines, that the engine & prop
controls were dependent on electric power and that the landing gear
used an electric motor would have stopped me from taking off until
the battery/electrical system problem was addressed.

Well said, and I wouldn't disagree. However, the very same potentially
deadly failure could occur anytime the battery fails inflight, with no way
for the pilot to know about it before he actually hits the button to lower
the gear.

No. This was not caused by a battery failure per se. It was a failure
of the electrical excitation system which starts the alternators. That
should prevent the engine from starting and it did. However, the pilot
bypassed that by starting both engines (a big no-no) with external
power. The battery is not actually used in-flight to keep the engines
running. The alternators are used for that, with a generator backup,
and finally a battery for backup, with warning lights all over the
place. Once the plane is flying, assuming the alternators start out
working, you would practically have to have a major electrical fire to
duplicate the problem. But take off without a working alternator and
you have a big problem.


--
Waddling Eagle
World Famous Flight Instructor