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DFC90 - Sudden "Autopilot Disconnect" in Cruise

I have updated the firmware of my bicycle twice in the last months.

I have seen a water tap with firmware updates.

Programmable microcontrollers are great because you can sell non working products and fix them later. Saves a lot of QA.

It's a whole new world out there now

Administrator
Shoreham EGKA, United Kingdom

Actually I think most automatic gearboxes of higher performance cars are sw controlled today. Makes sense, doesn't it?

The problem is that even the truck and Unimog technology got so high tech today that we have to send our technicians to courses all the time, buy and install new software all the time ...

If we live that long the mixer in a GA airplane might be moved by a computer. But then... I'll probably not live another 150 years :-)

Talked to a Senior Technician of Avidyne this morning.

Result: The DFC90 Autopilot has a en error log but the A/P has to be sent in to Boston for that, and will then be sent to their lab in Colorado. It has to be taken apart and the "Simcard" (that's the word he used) has to be take out to be analyzed.

The log will not specify WHY the autopilot has disconnected, it will only list "disconnected" ;-))

Now, I don't think I have to send it to Colorado for that. I already now it disconnected.

Avidyne thinks that the too high voltage (3.5 volts) instad of maximum 3 volts (2 is better) is the reason for the problem, and the techncian said that it is very likely that the "microswitches" inside the roll cartridge (that's what the whole role servon aaembly in the Cirrus is called) failed.

Avidyne thinks that the too high voltage (3.5 volts) instad of maximum 3 volts (2 is better) is the reason for the problem, and the techncian said that it is very likely that the "microswitches" inside the roll cartridge (that's what the whole role servon aaembly in the Cirrus is called) failed.

What would microswitches be doing in the roll axis?

I would expect to find them in the pitch axis, for detection of pitch servo torque limits (causes the pitch trim servo to be driven to bring the torque back within limits).

the A/P has to be sent in to Boston for that, and will then be sent to their lab in Colorado

To me, that sounds like Avidyne are contracting their R&D to a (nameless to you) subcontractor in Colorado.....! Otherwise, why not, ahem, send it straight to Colorado?

"their lab" - reminds me of a phrase from Al Pacino.

Administrator
Shoreham EGKA, United Kingdom

It is fine to trust the company, and I used to for years, but in GA not many companies are good. I have had a long string of in-flight problems, caused by incompetence. Stuff like the elevator trim freezing because they put some dodgy lube in

Sounds like you got lucky then. A friend of mine picked up a Twin Comanche after an overhaul by supposed Twin Comanche experts and discovered while over the Irish Sea it was pumping significant amounts of fuel overboard (which implies that had it not been detected, the pilot might have gone swimming). After diverting to Blackpool, it was found that one half of the fuel system had been put together with nearly criminal incompetence.

I have to wonder what all these licensing requirements for engineers are for if they can do things like that.

Andreas IOM

Peter, I don't know the details, but the tech explained to me that inside the Cirrus roll trim cartridge (that's the whole role servo mechanism in Cirrus acft) there are several tiny microswitches and that these can go bad after a couple of years. Now that the roll servo has to be exchanged anyway it will all be new.

Actually I have a good feeling with Avidyne. They really seem to care and they already talked to Avinik Straubing about it.

Actually I think most automatic gearboxes of higher performance cars are sw controlled today

Not just higher performance cars, all automatic cars, tractors, construction machinery, etc, etc. My company has been making transmission controllers for tractors for well over 10 years. These days the clutch pedal is a big spring and a sensor!

Darley Moor, Gamston (UK)

Yes, I know. we are selling Mercedes UNIMOGS ... the newest model has mor electronics than most planes :-)

I visited Avionik Straubing the other day and their Autopilot Specialist Martin Scheifl (big recommendation!) listened (listened!) to my complete story and then made an analysis.

He dismissed the following ideas which i got from all aroud the globe:

  • Autopilot Roll Servo Startup Voltage: there is NO feedback (wire) from the servo to the A/P

  • He also would NOT replace the servo because of the 3 volts as long as the plane flies as precise as it does (he says that a new servo will be at 3 volts within a year again and that its a waste of money)

  • Out of trim: not possible because there would have been a "servo limit" message

  • Bad A/P rack: If the rack is bad and has no good connection then it will not work for three months and be bad just for two flights ...

We will now try to get a new A/P computer. It still has two years of warranty, and Martin says that the only thing he can think of is that the A/P computer has a problem.

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