The International Cessna^® 170 Association

I have a 1950 170A and am in the process of completing a new circuit breaker setup and replaced all switches and grommets in the keys. There is a black unit on the back middle of the piano keys that I am trying to figure out what it is for (See Pic Attached). Power was wired to it through the landing light switch, as well as the wires that go out to my landing/taxi light. I am putting the landing and taxi lights on their own switch. Just curious if anyone knows what this unit is and what is wired to it. I have looked through the manuals and such and cannot identify it. I will do some continuity testing on it this weekend when I am back up at the plane.

I had a 1950 Cessna 170A a few years back and it had the same device on the piano keys and wired to the landing light
If I recall correctly, it was a double pole double throw switch that controlled the landing light circuit. I could be mistaken. Others more knowledgeable than me can help you with your question. But this is an early take.

Have you looked at the Illustrated Parts Catalog for your serial number airframe..? (Self resetting circuit breaker 2A, for the T&B and/or stall warning)

I'll confirm George is correct. It is a self reseting circuit breaker for the T&B and stall warning.

Are you certain power to it is THRU the landing light switch..? It should have it’s power supplied continuously…. not only when the land/light switch is activated. Perhaps it’s wired/sourced on the “hot” buss side of that switch?

Yeah power is being pulled rom the load on the landing light switch. So not the line from the switch. Very thankful for your input. Would it be better just on a standard 2A breaker by itself? Looks a tad rusty inside. I checked my IPC but was a bit confused. Yours actually shows the breaker…mine doesn’t. Quite interesting.

I don’t have a turn and bank indicator anymore so it’s just powering the Stall Horn….which I recently rebuilt and got working! Have an AV30 for turn and bank.

You all rock!

If the auto-reset breaker still works…I’d keep it. You certainly can replace it with a common breaker OR fuse…just log it, IMO.

Auto-reset C.B.s are not expensive.

I just bought a new one. This one had cracks in the housing and looked like it had been glued.

I’ll roll with what they said to roll with. Excited to get this bird all redone.

Thanks so much for your knowledge.

AC43.13-1B Paragraph 11-50 (b):

43-13-1b is acceptable methods not absolute requirement. The mfr'r (Cessna) had their reasons and their design is approved. If the self-resetting C.B. were hazardous I’d think an AD or at least a Service Ltr or Bulletin would have been issued by now…. and perhaps it has..

“not recommended”…. I believe is a General Statement…. (and a good one)…but not absolutely-applicable in this instance where it was Certified in the original Airworthiness and Production certificates of the airplane. This particular C.B. supplies what is/was considered “essential equipment” … the Required-Equipment Stall-Warning system in the B-model… and the T&B instrument…which was also required equipment as a non-tumbling, emergency attitude instrument. (In fact, the original IFR certification made the T&B req’d Equipt.)

Re-setting Any circuit breaker one-time while “in flight” used to be taught as standard-practice. That has changed …the current (pardon the PUN) thought being that if a particular circuit was shorted sufficiently to “pop” the circuit-protection…. RE-setting the C.B. might stress that circuit-wiring a second (or third, etc) time….each event further damaging the wiring…. possibly leading to in-flight fire.
The recommendations today are …if a C.B. “pops” in-flight…. consider whether or not that circuit is absolutely necessary to complete that flight. If Not…then Don’t re-set the C.B. at all. Have it investigated at the next opportunity.
The recommendation of AC 43.13 makes sense in that consideration.

The 172C I own failed to start once on a trip. I hand propped it and continued the flight…and later discovered the T&B was not indicating. It had failed with an internal “short”. The self-resetting C.B. did not because it sensed the failed T&B….and the starter circuit req’d that circuit for initiation. It was a learning experience for me… I never dreamed a failed T&B could prevent engine start.