Stall warning malfunction - 1959 Cessna

Leo O'Farrell

Leo O'Farrell

Pre-Flight
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Jun 25, 2011
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65
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Lakeport, CA
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Leo O'Farrell
During pre-flights over the past month or so, I power up the Master and check lights, stall warning buzzer and fuel gages. The stall became intermittent and has now gone non-existent.

I flew Saturday and did some power off stalls just to confirm, and there is no warning at all.

Wondering how to go about checking what is wrong? The reed moves fine and doesn't seem any different.
 
I assume this is one of the little flippy vane ones from that era (as the later party horn warnings wouldn't need the master).

If the thing doesn't sound when you push it up by hand, it isn't going to work any better in the air. I assume you've done all the standard pilot things of checking the breakers/fuses.

It's not that elaborate of a circuit. The switch (which is likely the culprit). Thing comes off the 2A CB to the common terminal on the switch, NO on the switch goes to the buzzer and then the other side of the buzzer is grounded. Shouldn't take much effort to diagnose.
 
Those things are outrageously expensive to buy from Cessna. If memory serves, they were about $1200 when mine was acting up 6 or 8 years ago. We removed it from the wing, cleaned it up with electrical contact cleaner, and it's worked flawlessly since.

I THINK there are two wires hooked to the back of it. If you take them off, contact them together (assuming it's a normally open circuit), and the stall warning goes off, then it's the "little flippy vane" that's bad. If the stall warning doesn't go off, then it's the buzzer that's bad or a wiring issue.
 
It's usually that cheap little microswitch behind the flapper that's bad. It gets dirt and crud in it. It can be cleaned a bit, but the switch itself is not expensive.

Dan
 
If it's a "Safe Flight" switch, and I believe that's what Cessna used, They are ridiculously expensive. But, as Tim said, they can be cleaned. BTDT.
 
Thanks for the experience shared and tips on cleaning, etc. I'll try this soon at the airport when next released. Going to buy a can of contact cleaner.

I've seen the horn/buzzer before when removing the glove/map box, it's a huge device, so hopefully it's as clear cut as it sounds to fix.

I'll report back.


Leo
 
Dan Thomas said:
It's usually that cheap little microswitch behind the flapper that's bad. It gets dirt and crud in it. It can be cleaned a bit, but the switch itself is not expensive.

Dan
Click to expand...
The switch can be cleaned but not replaced (legally). The microswitch looks like something you could buy off the shelf for $3 but it's specially made for Safe Flight and you can't buy a new one from anywhere else.
 
I think I recall some guys on the various Cessna forums saying to drown the switch in electrical contact cleaner to get it functioning again and then hit it with some CorrosionX or more electrical contact cleaner at every annual to keep it in good working order.
 
Yeah, they are outrageously expensive for a simple switch- a light switch is more complicated. When mine went out the price was $1400. Mechanic cleaned it up and it worked fine. He told me, "That will be $1200. I just saved you $200."
 
OK, picked up a can of electrical contact cleaner, remove the four screws holding the stall warning in place, one inspection plate and was able to remove the stall warning indicator device.

Unhooked the wiring and spray cleaned without opening it up any further.

It now works fine. Thanks for all your suggestions/experience.

Leo
 
Blackhawk said:
Yeah, they are outrageously expensive for a simple switch- a light switch is more complicated. When mine went out the price was $1400. Mechanic cleaned it up and it worked fine. He told me, "That will be $1200. I just saved you $200."
Click to expand...

I hope that was said tongue-in-cheek. :confused:
 
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