Fuses and the DA42 (Twinstar)

[cre8flyer]

OK. . . this is going to sound weird. . . but the technological marvel of the DA42. . . you'd assume there would be only circuit breakers and no fuses, but I found at least 4 circuits which, per the maintenance manual, have fuses in them. There is even a diagram showing the fuse for one of them - so its not just that they used the word "fuse" incorrectly and really meant "circuit breaker".

1. The hot bus (20 amp)
2. The landing gear (50 amp)
3. The excitation battery
4. The "glow" fuse

Now. . . I learned way back that if you want to fly at night you have to have spare fuses accessible to the pilot in flight (91.205 (c)(6)).

Is there an "out" somewhere that allows these airplanes to fly without spare fuses? e.g. the fact that the fuses are installed where the pilot could not reach / change the fuse in flight?

[Berkut]

Originally Posted by cre8flyer

Is there an "out" somewhere that allows these airplanes to fly without spare fuses? e.g. the fact that the fuses are installed where the pilot could not reach / change the fuse in flight?

Check out 23.1357(d) and (e).

(d) If the ability to reset a circuit breaker or replace a fuse is essential to safety in flight, that circuit breaker or fuse must be so located and identified that it can be readily reset or replaced in flight.
(e) For fuses identified as replaceable in flight--
(1) There must be one spare of each rating or 50 percent spare fuses of each rating, whichever is greater; and
(2) The spare fuse(s) must be readily accessible to any required pilot.

[cre8flyer]

OK. . . what am I missing? The fuses are not in the cabin, e.g. the fuse on the excitation battery circuit is behind a panel in the front baggage compartment.

So far I'm understanding that all DA 42s are not FAR compliant because the fuses are located where the pilot cannot reset them AND there are no spare fuses in sight.

[Swen]

Originally Posted by cre8flyer

So far I'm understanding that all DA 42s are not FAR compliant

Either that, or the 4 circuits and associated fuses you've listed are not considered "essential to safety in flight."

Strange.

[Berkut]

Originally Posted by Swen

Either that, or the 4 circuits and associated fuses you've listed are not considered "essential to safety in flight."

That's likely it. Or rather, it was determined during the certification process that these fuses weren't required to be pilot replaceable due to low probability of failure. Check out this document:

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgPolicy.nsf/0/23080994efad2d0a86256e44004be9b3/$FILE/circuits.pdf

[OldTownPilot]

All the more reason Diamonds suck.

I'd personally like the hot bus and the gear on a CB but thats just me.

No idea what the excitation battery and the glow fuse are. whatever, diamonds suck.

[xpanterica]

Originally Posted by OldTownPilot

All the more reason Diamonds suck.

I'd personally like the hot bus and the gear on a CB but thats just me.

No idea what the excitation battery and the glow fuse are. whatever, diamonds suck.

Hmm... I really rather enjoy flying DAs. If it weren't for the inaccessible fuses, what else is there that bothers you?

[killbilly]

Originally Posted by OldTownPilot

All the more reason Diamonds suck.

I'd personally like the hot bus and the gear on a CB but thats just me.

No idea what the excitation battery and the glow fuse are. whatever, diamonds suck.

Not sure about the excitation battery, but in a diesel motor the glow plugs are whats used in place of spark plugs. Am I wrong?

[roundout]

Originally Posted by killbilly

Not sure about the excitation battery, but in a diesel motor the glow plugs are whats used in place of spark plugs. Am I wrong?

Yes, you are wrong. A glow plug is used to assist in starting by heating the cylinder walls to a temperature at which combustion can be supported. They come on, do their job, then turn off before you start the engine. In many modern diesels, including the engines on the DA42, the glowplugs come on briefly again after light-off to help with smoke, vibration, and noise, but then turn off for good.

The landing gear is on a CB accessible to the pilot.

[OldTownPilot]

Originally Posted by xpanterica

Hmm... I really rather enjoy flying DAs. If it weren't for the inaccessible fuses, what else is there that bothers you?

Rudders that fall off, AHRS that doesn't work. Lets just say its fun being a fly on the wall at a Diamond service center.

[Polar742]

Back to the OP.

What does the POH say? Is it certified for DAY-NIGHT-IFR? If so, then it's all good.

Remember, there are ALOT of exemtions to FARs assigned.

There are ALOT of planes with CB/Fuses you can't get at inflight. The POH diagrams (I haven't seen a Diamonds) are usually dumbed down for pilots anyway.

Sorry for the simplistic explination, but as an operator, with a POH signed by the FAA and the conditions certifcated on the placard, the machine has completed the Fed's vetting process.

[trafficinsight]

The main reason they hide fuses and breakers from pilots is that they don't want the pilot to be able to replace or reset them in flight. For example, the heater temperature switch on a combustion heater.

We had a pilot completely fry the electrical system and avionics stack on a Duchess because he held the right alternator breaker in when it kept tripping.

The other alternator was working fine.

[roundout]

Originally Posted by OldTownPilot

Rudders that fall off, AHRS that doesn't work. Lets just say its fun being a fly on the wall at a Diamond service center.

I'd like to know why the rudder fell off. Bet you a pizza that it was improperly installed by the service center. The rudder comes off as part of the 100hr/annual inspection on the DA40 and DA42. I don't know if it is removed on the DA20. Either way, I doubt that two attach points could fail if the rudder is installed properly.

AHRS is a Garmin problem, not Diamond.

I would encourage you to spend an appreciable amount of time at a service center of any other manufacturer and listen to the mechanics complain about those aircraft. I think you'd see that mechanics complaining is not a symptom of being a Diamond service center, but of being a mechanic.

[cre8flyer]

The only "appliance" attached to the hot bus is the pilots map light. While usefull, I'm not sure I'd call it essential for safe flight.

The excitation circuit on the other hand. . . this is an additional battery that was added as a result of a fatal accident after dual engine failures, i.e. both engines quit when the electric system shut down due to the voltage spike caused by gear retraction. The excitation battery was added to ensure that even if the voltage regulators take the alternators off line (due to a voltage spike), and the battery is dead (pilot map light was left on for several days before the doomed flight), there will still be enough electrons in the system so that the engines continue running.

I'd say that battery is pretty important to safe flight. . . and that's the one for which they actually show the fuse in the system diagram.

[Johnsc81]

A&P from a Diamond Service Center here.... And my first word of advice.....get rid of the DA-42..... Ok, let me re-phrase that, get rid of anything with the Theilert Engines...... (TAE installation/Service Station too).

But to answer the original question. The C/Bs and the Fuses are two different things, the manual does group them as one thing, but they are definately two seperate items. The C/Bs are resettable by the pilot, therefore compliant to the FAR. However the Fuses are "Slow Burn Fuses" meaning that when they go, they have absorbed enouph power that you do NOT want to replace them until the mechanic finds a problem with the wiring.

Few helpful hints.....pay attention to the rear door hinges (Cracks), the main gear hinge pins (corrode and fall out), and the main gear door attachment bolts (corrode and fall off). We have lost a few of those in flight. Also pay the mechanics to paint the bell cranks in the wheel well, and remove all corrosion in and around the gear, it will save you a lot in the long run! Anyone having problem producing enouph power on the ground and then overspeeding the props in flight?.... Ohh yeah, have a ready supply of door lock cylinders. And pre-order anything from Theilert by at least a 6 weeks....... I could keep going, but there is not enough space.....

And there is a new service bulleting out......recommend having it done as soon as possible.....

[Johnsc81]

Originally Posted by roundout

I'd like to know why the rudder fell off. Bet you a pizza that it was improperly installed by the service center. The rudder comes off as part of the 100hr/annual inspection on the DA40 and DA42. I don't know if it is removed on the DA20. Either way, I doubt that two attach points could fail if the rudder is installed properly.

AHRS is a Garmin problem, not Diamond.

I would encourage you to spend an appreciable amount of time at a service center of any other manufacturer and listen to the mechanics complain about those aircraft. I think you'd see that mechanics complaining is not a symptom of being a Diamond service center, but of being a mechanic.

Did I mention I worked for a Cessna Service Station too (not to mention all my Turbine experience too, Boeing and Airbus included). I Would Much rather have a Cessna or even a Piper, or even a Beechcraft (beechcraft hates Mechanics!), then a Diamond. Not that they are hard to work on (quite the Opposite, they are one of the easiest a/c to actually do work on), but that they are always breaking. And as far as the rudder goes.... wouldn't assume the mechanic at first. they only have one real attachment point, the other is just a pin (facing down at that). you loose the main bracket and the rudder literally slips off. I can have one removed in under 3 minutes, (2 nuts and it is off) and that is doing it according to the book. For a cessna......at least an hour....... for a duchess....talking a couple hours.....

But in all honesty.....complaining is part of being a mechanic, we do get pretty good at it...... after all, our jobs is basically fixing other peoples mistakes....

[killbilly]

Originally Posted by roundout

Yes, you are wrong. A glow plug is used to assist in starting by heating the cylinder walls to a temperature at which combustion can be supported. They come on, do their job, then turn off before you start the engine. In many modern diesels, including the engines on the DA42, the glowplugs come on briefly again after light-off to help with smoke, vibration, and noise, but then turn off for good.

The landing gear is on a CB accessible to the pilot.

Thanks. I knew it was something like that.