URGENT!! EFIS failure in IMC

[billkennedy3]

Well, the nightmare happened. EFIS failure in IMC with an emergency descent using a nickle-dime 2.25 inch turn and bank instrument. I had a 5,000 foot penetration through solid clouds. Holy Crap -- it wasn't pretty, and I can assure everyone that it wasn't much fun. I can thank the fact that I broke out at 4,000 AGL more than my flying skills for an uneventful ending. Here's what happened.

1. As I entered the clouds in a climb (4500 AGL) my EFIS display started to flicker fairly steadily. It had happened the last time I was in the clouds as well, but not before that.

2. As I leveled at 10,000, my attitufe indicator went to a 20 degree climb indication and seemed to freeze. I'm guessing this was after five minutes or so of flickering.

3. Moments later, my heading system died and disappeared with some kind of cryptic message where the HSI had been.

4. At this point I was trying to fly off of the standbys, and ignoring the EFIS.

5. A short time after I got into VMC, my EFIS CPU shut down. I was not able to get it back up -- even after landing. My display went bright white.

My plane is grounded now. I'll talk to BMA tomorrow about troubleshooting and fixing the system.

My recommendations to fellow pilots:

1. At the first sign of unusual EFIS operation, get your butt into VMC and stay there.

2. Before anything like this happens to you, get proficient with your backup system -- it may be really important to your future. You can bet I'll be better next time.

3. Fly Safe!

[ddouglas]

Bill,
If the onset of the problem was simultaneous with cloud entry, it makes me think that p-static might be responsible. What kind of clouds were they, and what type airplane were you flying?

[billkennedy3]

I'm suspicious of static electricity too, but the clouds were the standard NW stratus crude. I did have some mild turbulence once I entered the clouds though -- maybe that's enough. Type of aircraft is Lancair 320.

[ddouglas]

Bill,

Scary. Please let us know what BMA finds and how they recommend that you deal with it.

I spent many years researching precipitation static for the military. It can be virtually assured when flying through ice crystals, snow, or dust. Water-clouds didn't cause as much--at least it didn't rise to the level of our concern then--but it is known that it can and does cause electrification of the vehicle. Interference with electronic devices can occur when the electric potential of the airframe exceeds the breakdown threshold of air...about 30,000 volts... and the excess charge on the airframe leaves in the form of corona (tiny arc-like) discharges. These discharges leave the airfame from places of small radii--like wing tips, trailing edges, and so on--places where the electric field strength (in volts/meter) is highest.

While the charging and discharging cannot be prevented, metal airplanes can reduce the threat to avionics devices by placing static dischargers at the high-field regions. These dischargers are designed with tips that break down easily (i.e., at low potentials) and have a large resistance between the airframe and the discharging tips to "separate" the discharge from the airframe and to reduce the discharge energy. (Less expensive dischargers have a carbon-loaded cotton wick. More expensive types use molded resistors and very sharp sintered tungsten discharge needles.)

Fiberglass airplanes are more of a problem because the dielectric surfaces hold the accumulating charge until the surface stress becomes sufficient to discharge across the surface (and eventually off into the air). If the charge doesn't migrate freely to a discharge location, static dischargers don't help.

The spectrum of p-static discharge energy has its peak in the 100 to 300 kHz region, so one wouldn't expect to "hear" the noise using VHF (100-150 mHz). Loran or ADF, receivers, on the other hand, would readily detect p-static.

I doubt that BMA has tested their system for its hardness against conducted interference. To gain some data in this area, I would be useful if others with exerience of unusual upset of their EFIS would describe that in terms of the circumstances, the weather and cloud type, airplane type, and so on.

This has happened to me a number of times, and I have posted a number of warnings about using only electrical flight instruments on this site. I fly a Lancair 360. Is there anything we can do about it?

[billkennedy3]

Question for ddouglas:
Is there any relatively simple power conditioning I could do for the EFIS CPU that might protect it from possible static electricity?

Question for N99CR:
What do you do to reset your EFIS following failure? My CPU seems to be dead to the world. Power reset does nothing. I'd venture a guess that the display unit is okay and something in the CPU is smoked.