DA 42 accident

"Cary" wrote in message
oups.com...
The problem, as I understand it, was the battery was dead. According
to the POH, the battery is used to start the engine and is used as a
backup during flight for all the electronic gear (including the
FADEC). Although the investigation is still ongoing and other answers
may be forthcoming, when they operated the landing gear they exceded
the power available from the alternators and the backup system (the
battery) was not available so the FADEC (engine computers) stopped.
One of the lessons here is that one should not fly an airplane that
relies on electricity if you don't have a battery to run the
electricity!

Cary

On Apr 23, 4:35 pm, wrote:
Gig 601XL Builder wrDOTgiaconaATsuddenlink.net wrote:

Neil Gould wrote:
A simple voltmeter with a "red line" should suffice, along with a
caution; "Don't take off with the needle outside the green arc". Of
course, that won't prevent someone from insisting on making a bad
decision.

I again agree but if you are going to have an sytem with FADEC it ought
to
have the authority to to clearly tell you that it is about to use its'
authority to shut the engine off.

From the description it sounds more like the FADEC didn't have the
authority (or power) to do anything.

More to the point, if all the power goes away, what happens to all
the "settings" the FADEC controls?

Do they go to zero, full, stay where they are?

It appears that they go to zero, which is a damn unhandy failure mode.

--
Jim Pennino

Remove .spam.sux to reply.



Even if the battery worked fine, something that causes damage, even
something as small as a bird strike can cause a short; dropping voltage,
and shutting down the engines, plural. Wouldn't a relay that isolated the
engine when the buss voltage dropped to zero have helped? Surely some
prioritizing is in order.

Al G

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

Karl-Heinz Kuenzel wrote:
I did not believe it either. Maybe I am getting to old. For me a
diesel would run forever until you cut the fuel.

not with a common rail fuel supply. The injectors won't open without power.

The main point as far as I'm concerned is, that this is not a particular
problem of the thielert or aerodiesels in general, it's a problem you get
with engines depending on electrical power. This dependancy on electricity
is somehow the price you pay for better fuel efficiency, more comfort and,
as far as the engine itself is concerned, less "finger problems" and
therefore more reliability. As the article itself states, it is not a big
issue to create a redundant system that will eliminate the risk of a single
point electrical failure shutting down an engine, let alone both.

What those people did. They just started #1 and #2 (which was NOT ok)
on external power. And everything looked ok. Until they retracted the
landing gear....

I posted that story in our German newsgroup and nobody seemed to be
interested in that issue. I was just curious, if someone here is
interested.

I'm not a pilot, though I enjoy flying in small aircraft and I have some
technical interest in aviation. As a development engineer in automotive I
particularly like to learn about aeroengines and I somewhat follow the
development of the aerodiesels. I'm mainly lurking here...

regards,
Friedrich

More to the point, if all the power goes away, what happens to all
the "settings" the FADEC controls?

Do they go to zero, full, stay where they are?

Without electrical power, apart from the fact that the FADEC is a computer,
and no computer will run without power, on a common rail diesel the
injectors cannot open. A purely mechanical "limp home" mode is physically
not possible. Multipoint or direct injected gasoline engines are the same.

It appears that they go to zero, which is a damn unhandy failure
mode.

Yes it is, but that's just the way it is. It's no different from the failure
mode you get when your fuel supply or both magnetos fail or something
similar. That's why the power supply of a FADEC should be held to similar
stringent redundancy requirements. Actually, the FADEC itself IS double
redundant but fed from just one battery. Go figure.

regards,
Friedrich

On Mon, 23 Apr 2007 21:35:03 GMT, wrote:

It appears that they go to zero, which is a damn unhandy failure mode.

It's the new, revolutionary fail unsafe mode.

--
Dallas

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.

"Newps" wrote in message . ..
:
:
: Thomas Borchert wrote:
:
: Blueskies,
:
:
: Doesn't the 1.7 have a throw away TBO-like limitation that is very low?
:
:
:
: No. it has a TBR (r for replacement) of 2400 hours, guaranteed by
: Thielert. When you buy the engine, that price buys you 2400 hours. Can
: you say that of any Lycosaurus or TCM?
:
: yes, they currently do replace the engines sooner than that - but you
: don't pay for it. They're working up to final TBR.
:
:
: What does it cost the owner at 2400 hours?


A new engine...

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

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

On 2007-04-24 09:09:14 -0700, Cary said:

The problem, as I understand it, was the battery was dead. According
to the POH, the battery is used to start the engine and is used as a
backup during flight for all the electronic gear (including the
FADEC). Although the investigation is still ongoing and other answers
may be forthcoming, when they operated the landing gear they exceded
the power available from the alternators and the backup system (the
battery) was not available so the FADEC (engine computers) stopped.
One of the lessons here is that one should not fly an airplane that
relies on electricity if you don't have a battery to run the
electricity!

Actually, if the battery is dead the alternators will never start
working. This is the excitation battery system that failed. Its sole
purpose is to supply enough current to excite the alternator when the
engine is started. After that it is never used again during the flight.

The DA-42 has considerable redundancy. Click on the electrical diagram
in the article and you can see the problem immediately. This particular
airplane has two alternators *and* a generator. If the alternators do
not work (as is probable) then the generator kicks in. The generator,
however, is not big enough to operate both landing gear and engine -- a
possible design flaw. Also, if you are going to have a generator, why
not use it to excite the alternators if the excitation system has
failed? Apparently the designers assumed that if the generator is being
used that the alternators have failed beyond repair, but here it might
have been possible to get the alternators working with a full
complement of power. On the other hand, maybe the original problem was
the alternators were both dead (doesn't seem likely) and that is why
the excitation system was dead. So even current from the generator
would not have excited the alternators.


--
Waddling Eagle
World Famous Flight Instructor