[basloane]

Hi Mark

The circumstances and details of your problem sound very, very similar to a problem I had with my landing gear. The only difference is that I was in the air when it happened.

While approaching to land, I selected gear down, the doors opened, the gear came down,…. and then the horn started blaring. I paused for a few seconds, uttered a few expletives, and then selected gear up….the gear remained extended. I performed all the required checks, gear up, gear down, hand pump, and even a few (utterly silly ) checks, but the horn continued with no green light. We looked in both wing mirrors; the nose wheel seemed to be in place, and we could see both mains. I could also see that the gear doors were open. The horn continued with no green light.

As I began to think about my landing circumstances, suddenly the horn stopped and the green light came on. The subsequent landing was uneventfull.

With the assistance of a local mechanic, I inspected the gear system, checked hydraulic levels, etc. and found nothing amiss.

When the problem reoccurred a few flights later, I decided to "take the gloves off" and meet this head on!

We jacked the airplane and performed 10 flawless retractions. We were about to deem it a "non-problem" and declare "Miller Time", but then I decided to do one more test using the hand pump. On this final try we were able to duplicate the problem. After 10 minutes of searching for the problem, we discovered that the Gear Indication Breaker had tripped. We reset the breaker, and everything returned to normal.

I called my ( previous ) mechanic, and he pointed out to me that the reason the doors did not close and that there was no green light, is because the circuit which contains the three down and locked switches was not allowing current to go thru the indicator circuit. The gear probably is down and the switches are closed. He advised that I VERY CLOSELY examine the wiring within 6 inches of each down/lock switch, looking for any evidence of electrical malfunction or shorting. Be sure to look and feel behind the wire, because the damaged part of the wire may be hidden from view. This can be done without jacking the aircraft.

Near the right Main Gear Down/Lock Switch we noticed a very tiny blackened area on one of the wires within about 50 millimetres from the down lock switch. On close examination we could see the physical and thermal damage ( electrical arcing soot ). We performed a ( mickey mouse ) "test" fix, cycled the gear up and then down as we watched the process. During gear extension, the doors completed opening and the “locking dog” retracted to prepare to accept and hold the gear as it deployed into position. The wire became pinched between the dog and the airframe panel. We saw an electrical spark.

We then removed the Mickey Mouse fix and applied some of that "spiral Teflon wrap" to each wire individually, then to the pair together. We repositioned the wire a few millimeters higher so that it would avoid the dog when it retracts, and then did a couple of retractions and extensions. Everything appeared to work perfectly.

Interestingly, we looked at the left side, and it would appear that a repair has also been made to those wires. We are guessing that someone in the past has experienced a similar occurrence problem.

My experience prompted me to think through the manner in which the Engineers designed and arranged these wires. These wires must be located and oriented no lower than, or ( ideally ) EXACTLY as, was intended from the factory. If that last 6 inch portion hangs a few mm too low, it could become vulnerable to pinching between the downlock "dog" ( when it activates to accept and release the gear ) and the adjacent airframe panel.

In my case, the switch appears to have been replaced by a previous owner, and rather than threading the wire up into the local "P-Clamp", it was merely attached to the outside of the clamp with a tie-wrap. This caused the wire to hang a few mm lower and make it vulnerable to pinching.

My only explanation for the mysterious silencing and restarting of the system is that the cloth of my pant leg brushed against the tripped breaker and reset it. This particular breaker is a low current breaker and requires very little pressure to push it back in.

An interesting experience to say the least. I hope this helps you with your problem.

Best Wishes,......Barry Sloane, N187