Aux Power Cable Short

patrolpilot · #1 08-04-20, 05:08 PM

About a week and a half ago, I experienced a total loss of electrical power just as I leveled off at 2000'. There was a powerful electrical smell in the cabin; I saw a puff of smoke go through the vent window (it was open because the temp and humidity were unbearable). As I reached for the master switch, never quite touching it, the airplane experienced a total electrical failure. I turned around, ran the "Electrical Fire In Flight" checklist, and then got busy pumping the gear down. While pumping the gear down, I called my mechanic via my phone (bluetoothed to my headset) to come out and give me a visual check on the landing gear and to see if I was trailing any smoke. I had added mirrors for both situations, but it's great to hear a "you're good."

I still had an active short smoking the battery after shutdown. The mechanic got it disconnected. The battery was "rocket" hot, and it couldn't be touched for about 30 minutes. We thought the new battery had shorted, but not so. Something else failed.

When my mechanic got to looking at what happened, he discovered that the aux power plug cable (which runs from the plug to the voltage regulator) had been rubbing against the front cowling flap actuator rod. This is very tough to see, down low on the firewall against the nose wheel well.

The short happened at the moment that I actuated the cowl flaps closed. The cable, once rubbed, immediately delivered the battery's capacity into the cowl flap actuator rod. The aux power cable has no breaker or fuse protection.

The cowl flap motor took the brunt of the charge, but there was some arching that cut the fresh air control cable. The "Electrical Fire In Flight" Checklist calls for the "Vents/Cabin Air/Heat" controls to be closed. The electrical burning smell was not dissipating in the cabin because the panel control actuation had done nothing.

It is a bit weird, to both my mechanic (an experienced 337 guy) and I that this OEM cable (Cessna PN on cable) is black. Usually, these large cables are white so that wear or heat indications can be viewed.

Bob Bena of RLB Accessory Service is rebuilding the motor. He said it is fried crispy, but he can handle it. I think if I sent it somewhere else, they would not have accepted as a core (yet, would probably rebuild it if I didn't pay to ship it back to me).

wslade2 · #2 08-04-20, 10:45 PM

I've been months in the shop and finally coming out but this was an area where we discovered some issues and "wire rot". Because of it's location, out of site out of mind, obviously neglected and overlooked by priors and a similar problem in the making. I'm an E model and it is under battery box. Be sure to take battery and battery box out and look down in this area all the way. Plus plenty of corrosion inducing gasses and dribbles in the region. Glad you're ok!

patrolpilot · #3 08-05-20, 06:05 AM

Quote:

Originally Posted by wslade2

I've been months in the shop and finally coming out but this was an area where we discovered some issues and "wire rot". Because of it's location, out of site out of mind, obviously neglected and overlooked by priors and a similar problem in the making. I'm an E model and it is under battery box. Be sure to take battery and battery box out and look down in this area all the way. Plus plenty of corrosion inducing gasses and dribbles in the region. Glad you're ok!

I'm still in my first year of ownership but have gotten to the point now that almost everything has been changed out. Somehow this cable, really though to find and almost looked like a protected control actuation cable of some type given is color and positioning.

edasmus · #4 08-06-20, 08:39 AM

Thanks for sharing your story. Nice job in your handling of the emergency. I have an email into my IA at Lumanair to have this inspected on my C337G.

Thanks again...,

Ed

edasmus · #5 08-06-20, 01:32 PM

Removed the battery and battery box this afternoon on my 1973 C337G and got a good look down there. There does not appear to be any issue on my plane as you described on yours. The wire in question on my plane must have been routed differently than yours as it is no closer than 5 inches from the cowl flap actuator rod. It runs from the back of the aux plug into a protective sleeve that runs under the battery box and then up the firewall still encased in the sleeve until the voltage regulator. I feel like (fingers crossed) all ok on my plane. Fire is scary.

Thanks again for your post.

Ed

patrolpilot · #6 08-06-20, 05:12 PM

Great to hear Ed. Not sure if the cable was ever changed out in the past. It is a Cessna cable, but not documented as replaced in the logs. All said, it did near $6K worth of damage.

edasmus · #7 08-06-20, 05:18 PM

Ugh.....$$$

We love our Skymasters, we love our Skymasters, we love our Skymasters...

Keep saying it until you believe it.... Lol... ;o)

patrolpilot · #8 08-06-20, 05:21 PM

Quote:

Originally Posted by edasmus

Ugh.....$$$

We love our Skymasters, we love our Skymasters, we love our Skymasters...

Keep saying it until you believe it.... Lol... ;o)

I hear you and I believe.

I'm not mad at it either, I'm old too and break. I bought it a cargo pack while it was recovering. I thought my mechanic was going to pass out when it was delivered to his FBO!