DA 42 accident

Newps,

What does it cost the owner at 2400 hours?


I seem to recall it's something like 20k for a new engine.

--
Thomas Borchert (EDDH)

Jose,

However, it does seem to be a serious oversight
that the engines themselves can't supply their own juice.


That will become totally common with FADEC engines. It's just DIFFERENT
failure modes we have to be used to - our current old engines have
single failure points, too.

--
Thomas Borchert (EDDH)

"C J Campbell" wrote ...

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.

I'm sorry, but the quoted article seems to point more at the main battery as
the culprit.

Without the buffering effect of the main battery, the current spike of the
gear retract was supposedly enough to decrease the voltage on the ECU bus
and cause an ECU reset.

There is a discussion whether the main battery was connected to the battery
bus at all. Judging from the electrical diagram, if the battery is flat
there is no way to activate the battery relay to get the main battery
connected to the battery bus.

If the excitation battery had been the culprit, I guess an alternator
warning light would have been very visible.

Recently, Friedrich Ostertag posted:

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 agree that a failure mode allowing in-flight engine shutdown due to low
battery voltage implies that there may be an aspect of the design that
needs attention. On the other hand, the dead battery could have been a
symptom of a larger problem, and the existing design really is quite
reasonable.

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.

Right, however, the alternator should be able to supply the electricity
needed to keep the engines running. It wouldn't surprise me to find that
the a breaker had popped when the landing gear was retracted and the pilot
didn't think to reset it.

Neil

"Neil Gould" wrote ...

If the alternators weren't excited, wouldn't the pilot be looking at two
alternator warning lights prior to take off?


According to the AFM there are amber caution lights for alternator failure,
so yes.


Does the aircraft have an
ampmeter?



Again according to the AFM, yes, but notably, it is not on the MFD's default
engine display page but on the "System" page together with the voltmeters.
You need to push a button to see it. However, the checklist requires you to
have a look at the "System" page after engine start as well as before
take-off, so if the checklist is followed a fault would not go unnoticed.

In the other scenario posited by the article, i.e. an unconnected main
battery, things become interesting. In this scenario the ammeters would
presumably show "normal" values, i.e the instantaneous consumption of the
electrical devices. In this case the voltmeter would really be essential .
The AFM says about the voltmeters: "Under normal operating conditions the
alternator voltage is shown, otherwise it displays the 'main'-battery
voltage." So the voltmeters presumably measure the bus voltage, and in this
scenario (battery disconnected) they would probably show an abnormal voltage
which could alert the pilot. I'm no expert here, but I seem to recall
stories of batteries failing in-flight and how that can be seen from the
voltmeter.

Also, in this case, there seems to be no way of positively checking the
actual, pure main battery voltage, because according to the schematic the
main battery relay needs power from the battery itself to operate and
connect to the battery bus. Or then I'm missing something......

Recently, C J Campbell posted:

On 2007-04-23 11:20:24 -0700, "Neil Gould"
said:

Recently, Karl-Heinz Kuenzel posted:

Neil Gould schrieb:
I have a somewhat different take on this event. [...]
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. I would find it surprising if Diamond doesn't
have adequate information about their flight systems in the POH to
inform the pilot of this possibility.


OK Neil.

You find it in the article.

My Deutsch is far too rusty to find it in the article. ;-)

POH - Under - abnormal operating procedures - 4B.7 STARTING ENGINE
WITH EXTERNAL POWER - #13 Opposite engine ..... START WITH NORMAL
PROCEDURE

That is it.

That's fine for starting the engines, but that isn't the only issue,
is it?

Is there nothing in the POH about the electrically powered items
(landing gear, FADEC, etc.)? If there is, it shouldn't require an EE
degree to realize that one should be concerned about the condition
of the batteries, charging, etc. if one has to "jump start" the
engine, or to realize that something critical is in need of
attention.

Maybe I'm just an overly cautious type. ;-)

Neil

No, you are not overly cautious. Every pilot should be taught that if
the battery is dead and you start the plane with external power, the
first thing you check is to see if the alternator(s) is charging. If
it isn't, either the alternator is broken or the battery did not
excite the alternator.

Now, if the excitation system did not excite the alternator, why
didn't the remote starting system do it? It should have. I would want
a look
at the power cart, its cables, and the wiring to the port on the
airplane. In fact, especially the latter, as it could provide a clue
as to why the excitation battery died in the first place.

If the alternators weren't excited, wouldn't the pilot be looking at two
alternator warning lights prior to take off? Does the aircraft have an
ampmeter?

Neil

Thomas, et al,
I agree about our legacy systems having single points of failure (SPOF);
but I would hope the new technology offered by FADEC would begin to
eliminate those SPOFs without introducing new ones. It appears to me that we
still have all of the legacy SPOFs and have now added new ones. Prior to
FADEC we didn't even have to have an electrical system to make an engine
run.

--
Jim Carter
Rogers, Arkansas
"Thomas Borchert" wrote in message
...
Jose,

However, it does seem to be a serious oversight
that the engines themselves can't supply their own juice.


That will become totally common with FADEC engines. It's just DIFFERENT
failure modes we have to be used to - our current old engines have
single failure points, too.

--
Thomas Borchert (EDDH)

"C J Campbell" wrote ...
Jose said:
I don't know the system, so I can't second guess the engineers
intellegently about it. However, it does seem to be a serious oversight
that the engines themselves can't supply their own juice.

They do -- with an alternator on each engine. There is also a generator.
How predictable is the failure of two alternators, the batteries, etc?

Chris,
I do not see the Generator to which you keep refering. Each engine has a
Starter Motor and an Alternator. The Airframe has a single Main Battery (10
amphour rated) and a series up Alternator Excitation Battery (1.3 amphour)
used "in the event of a main bat failure" (Diamond quote in POH). From the
article's diagram the magazine editor marked the excitation battery in RED.
I am not good enough with technical German to read the article, maybe
another reader can summerize the reason for the red highlight.

http://img.edsb.airworkpress.com/red/da42/esys_big.gif

http://www.pilotundflugzeug.de/artik...12/DA42_Unfall

I am a bit confused how that excitation battery is normally charged and how
the battery is monitored.

I also note that the Ground Power system is pretty standard looking in the
schematic, ie keep the Main Electric Master off and turn one Engine Master
on for starting so as not to have the bad battery connected and draw down
the Cart while cranking. But then what? You got your backup Battery excited
Alternator running your ECU on that engine, but it looks like you need to
keep the APU Cart connected because the power to activate the Alt relay can
only come from the main bus side. Is this normal for other twins?

Recently, Snowbird posted:

"Neil Gould" wrote ...

Does the aircraft have an
ampmeter?



Again according to the AFM, yes, but notably, it is not on the MFD's
default engine display page but on the "System" page together with
the voltmeters. You need to push a button to see it. However, the
checklist requires you to have a look at the "System" page after
engine start as well as before take-off, so if the checklist is
followed a fault would not go unnoticed.

I would think that this preflight requirement has implications for this
accident.

In the other scenario posited by the article, i.e. an unconnected
main battery, things become interesting. In this scenario the
ammeters would presumably show "normal" values, i.e the instantaneous
consumption of the electrical devices.

If the alternators are working, the ammeters should show a higher than
normal postive value, as the battery is not putting a normal load on the
charging system. That, too, would stop me from taking off.

In this case the voltmeter
would really be essential . The AFM says about the voltmeters: "Under
normal operating conditions the alternator voltage is shown,
otherwise it displays the 'main'-battery voltage." So the voltmeters
presumably measure the bus voltage, and in this scenario (battery
disconnected) they would probably show an abnormal voltage which
could alert the pilot. I'm no expert here, but I seem to recall
stories of batteries failing in-flight and how that can be seen from
the voltmeter.

Hmm. I'd think the alternator voltage would always be shown unless the
engines aren't running, and then the bus voltage is shown. A look at the
schematic could reveal which case is correct.

Also, in this case, there seems to be no way of positively checking
the actual, pure main battery voltage, because according to the
schematic the main battery relay needs power from the battery itself
to operate and connect to the battery bus. Or then I'm missing
something......

I'd think that checking when the engines are not running would show the
main battery voltage level. If the battery is dead, of course, the relay
wouldn't have power to connect to the bus.

Neil

Recently, Mike Isaksen posted:

"C J Campbell" wrote ...
Jose said:
I don't know the system, so I can't second guess the engineers
intellegently about it. However, it does seem to be a serious
oversight that the engines themselves can't supply their own juice.

They do -- with an alternator on each engine. There is also a
generator. How predictable is the failure of two alternators, the
batteries, etc?

Chris,
I do not see the Generator to which you keep refering.

On the schematic you're referencing, the Generators are the circular
symbols with the 'G' and labeled as such. However, as the relay in the
Generator circuit is labled "Alternator Relay", and there is an excitation
circuit I suspect that the terms are being used interchangeably. Not
technically correct, but...

Each engine
has a Starter Motor and an Alternator. The Airframe has a single Main
Battery (10 amphour rated) and a series up Alternator Excitation
Battery (1.3 amphour) used "in the event of a main bat failure"
(Diamond quote in POH). From the article's diagram the magazine
editor marked the excitation battery in RED. I am not good enough
with technical German to read the article, maybe another reader can
summerize the reason for the red highlight.

http://img.edsb.airworkpress.com/red/da42/esys_big.gif

http://www.pilotundflugzeug.de/artik...12/DA42_Unfall

I am a bit confused how that excitation battery is normally charged
and how the battery is monitored.

The excitation battery has a direct feed from both generators (really
alternators). If the fuse isn't blown, either alternator may be able to
charge this battery from excitation feedback. There is no indication of
how the battery condition would be monitored, but if neither alternator
operates, the excitation battery would be highly suspect.

Neil