"C J Campbell" wrote in message
news:2007042418074350073-christophercampbell@hotmailcom...
On 2007-04-22 04:23:22 -0700, Karl-Heinz Kuenzel
said:

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.

Karl

If you have to start both engines with remote power it seems to me that
is should be obvious that the electrical system is not working. If it
doesn't work with one engine running it is not going to work with them
both running.

According to the article, the battery was so dead that it could not
excite the alternator -- the alternator needs some current in order to
start. For example, if you hand-prop a single engine piston airplane
that has a dead battery, you might get the engine to run but you still
will not have an electrical system. The article complains about there
being a "single point of failure" for the plane, but in fact most small
aircraft have the same single point of failure. In the case of the
DA-42, however, electrical current is needed to keep the engines
running. This is a big difference from the piston engines most of us
are used to. This turns an electrical failure from a nuisance to
something deadly. The excitation battery system is needed to run the
ECU for each engine. Although each engine has its own bus, both are
dependent on the excitation battery system. If that fails, both engine
buses and the main bus go down. Since the excitation battery system
does not have anywhere near the power to handle loads like the gear,
the avionics, and the engine (and it was already broken), there was no
way this plane was going to fly.

The pilot should have known that if both engines needed to be started
remotely that this plane was not airworthy. Spending a little time
studying the electrical system of your plane can save your life. Look
at each component and ask yourself, what if it quits?

The props on most twin engine aircraft feather when they quit. It helps
prevent loss of control in an engine failure. Only piston single engine
props do the opposite in an attempt to keep the prop and engine turning
to make it easier to restart -- but at the cost of greatly reducing
your glide distance. Having a prop go to max rpm if it quits on a light
twin is likely to be deadly.

In general, it looks like a maintenance problem that was allowed to
turn into an emergency, which in turn was badly mishandled. One very
popular way of falling out of the sky is to take off in an airplane
that you knew had problems before you left.

All of that said, I think the article makes a strong argument that this
kind of thing should not happen. If you are going to have engines
dependent on electricity to keep running, then you need to have some
form of backup, but the DA-41 has a backup system -- it just didn't
cover what would happen if the alternator failed on takeoff and someone
raised the gear. I don't like the idea of the engines shutting down in
an electrical failure, either, but that is one price of FADEC. In the
DA-42, it appears that installing a generator was considered to be
enough redundancy in the event of an alternator failure. It apparently
never occurred to anyone that someone would take off with a failed
alternator and then try to raise the gear.

The question is why raising the landing gear should be allowed to cause
a complete system failure. The easiest fix would be to install a bigger
generator, but that is probably not a complete solution. I agree that
the electrical system should prioritize things, too. And if things
fail, I don't want just a red line on the voltmeter -- I want it to be
something that attracts attention to itself. In the DA-42, it appears
that there is an alternator failure light. This thing should have been
lit. Perhaps the pilot ignored it. Presumably the generator would keep
things running once the engine starts, but if all you have is the
generator I don't think you have any business departing the field. In
this case, the alternator appears to have never even started running
because of the failure of the excitation system, and the generator was
too weak to run the whole system, so it quit completely. Dang.

Yeah, I think there is a design problem, but it seems to me that the
pilot missed plenty of warning signs and opportunities to do something
about them.
--
Waddling Eagle
World Famous Flight Instructor

As you correctly pointed out, we will all have to wait for the accident
report to know very much. In my case, I already knew that the DA-42 had two
common rail diesel engines and was very fuel efficient--but nearly all of
the rest came from this thread. The result of what I am learning here is
that I am becomming less critical of the the aircraft systems and more
suspicious of a catastrophic series of human errors--from what I have read
in this conversation, it appears that, if a DA-42 is parked with the master
switch(es) on, and with the alternator exciter battery switches also turned
on, and the pilot did not understand the aircraft systems; then something
like this could easily occur.

Obviously, at this time, none of use know what really happened; but I am no
longer ready to presume that the systems lacked a normal level of safety.
In fact, I am no longer ready to presume anything--other than the fact that
I plan to read the report when available.

Peter