Friedrich Ostertag wrote:
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. That alone appears to me to be a major design flaw that would make
me pretty uncomfortable, batteries are known to fail suddenly sometimes. I
really would expect redundancy in something as critical as the power supply
for the fadec to be a requirement for airworthyness. Why have two sets of
magnetos on the typical SI-engine? It's just an electrical system, too...
Why have a twin engined aircraft?

I don't find it
surprising that the props feathered in this situation, and would even
say that it would be the expected behavior, rather than a fluke of
some kind.

If you are saying that a shut-down is to be expected when the power supply
on a fadec controlled engine fails, you are right. No modern engine will
continue running without electrical power. Even on a diesel with common rail
fuel supply (as the thielert is) without electricity no fuel injection is
possible.

regards,
Friedrich


This is a cut and paste from a AOPA story on the plane

There are three batteries. The main battery is a 24-volt 10-amp-hour
size. Electrical power is provided by two 24-volt 60-amp alternators —
one on each engine. There also is a 24-volt 1.3-amp-hour
alternator-excitation battery to provide alternator start-up
(excitation) voltage if the main battery is discharged below the
required excitation threshold. The third battery is a stand-alone
emergency battery that powers the electric artificial horizon and an
instrument floodlight for one and a half hours.

The question then become if there are 2 60AMP alternators and a single
10AMP-hour battery how could the battery being dead cause the issue. I
think there is much more here then meets the eye. Perhaps we should
wait for more data before we jump to conclusions.