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How critical is the stall warner switch?

Here you have the original stall warner switch (which perhaps 50% of Socata TB TKS installations are flying with) and below that is the correct one. Both seem to work… I think the reason is that you can operate the microswitch just by blowing onto the paddle, and the airflow in that location at Vs is helluva lot stronger than that.


At rest, the paddle is resting on the bottom stop, and it is there also in cruise. This is rather curious! A stall just moves it upwards. I never really thought about it…

Administrator
Shoreham EGKA, United Kingdom
Neil,

glider pilots in my country feel that they were skygods compared to any other aviators. So certainly they do not need any gimmicks to tell them how to fly. Surprisingly even them you will find in accident statistics falling out of the sky often enough in the last phase of landing because of not watching their airspeed. Here they don´t seem to be much different from us lowly motor pilots. And stall warning paddles disturbing air flow is just another ridiculous excuse not to have them installed. As to excuses, transponders are seen as too heavy/ too power hungry/ too expensive in relation to aircraft value and so on. I don´t want to get too detailed on glider pilots and their attitudes and special rights from the past. That would be another topic .

Vic
vic
EDME

Neil wrote:

Mooney_Driver wrote:
Non working stall warning would be a no-go

Another joke?

Not at all. According to the certification regs an aircraft must clearly indicate to the pilot that a stall is approaching. This can be done either “naturally” e.g. by noticeable buffeting or by a technical device.

If there is no “natural” indication and a stall warning device is installed instead, then the aircraft is indeed not airworthy with the stall warner u/s.

ESKC (Uppsala/Sundbro), Sweden

Neil wrote:

Another joke

Not at all. We don’t have a MEL on the Mooney obviously but I’d hesitate to fly with an inop stall warner. It is part of the certification and therefore imho required.

I so far have never had it go off unintended other than once at FL170 when Vs is a sight higher than on the ground and we tried to determine the absolute ceiling, but I have recently read a report of a take off accident on a short runway where the inop stall warner was cited as one of the reasons the pilot reacted wrong when the airplane did not behave as he expected shortly after take off.

LSZH(work) LSZF (GA base), Switzerland

I had a stuck stall warner making noise almost all the way on a 300 NM trip in an Arrow. While I believe in the safety of a stall warner in general, flying 2+ hours in that noise definitely detracts from safety. My 2 passengers were not impressed either. We never found anything wrong with the switch and as far as I know it did not happen again.

Last Edited by huv at 17 Feb 15:10
huv
EKRK, Denmark

I had the existing stall warner fail a preflight check, twice, many miles away from base, so I flew anyway. It never happened again… But this is why I ordered a new one for the TKS installation. And that is how I discovered there are two different types…

The old microswitch is working fine, of course

The case of a stuck switch is a good case for having a switch on the speaker I thought the TB20 had a CB on the stall warner circuit and just had a look and despite having about 1000 CBs it turns out that it is on a fuse.

Administrator
Shoreham EGKA, United Kingdom

We’ve had issued with moisture getting (blown?) into the assembly or affecting the wiring. So on the daily it would fail the test, but after a few hours in the sun it would start to work.

You are right they are a very basic design, but adequate enough as it’s possible to adjust them pretty accurately to +/-x knots. I believe the requirement is for it to come on 5-10 knots before the stall, and once adjusted correctly, it’ll come on pretty reliably.

It’s a non-MEL-able item, so considered pretty critical! I.e. it fails, the a/c is grounded.

Another joke?

Airborne_Again wrote:

According to the certification regs an aircraft must clearly indicate to the pilot that a stall is approaching… This can be done either “naturally” e.g. by noticeable buffeting or by a technical device.

Yes; and this obviously is not up for the pilot to decide. Goes back to the original design specification of the aircraft. If it was designed with a stall warner, that’s your cue.

Last Edited by Archie at 17 Feb 23:15

The case of a stuck switch is a good case for having a switch on the speaker

Doing this is just asking for other trouble. I once witnessed a sim-session (full-flight) as part of the Jet-Transition training. During approach stall training, the PF lowered the flaps too far before gear extension. The nuisance reminder of gear led the instructor pull the CBs (for EGPWS I think). Recovery was fine, as stick shaker was not concerned by that CB. But on the subsequent approach, the PF did not start the flare and (according to the sim) crashlanded on the runway. He immediately turned towards the instructor and claimed: There was no radio altitude callouts! That was caused by the pulled CB’s that were not reset.
What else is on your speaker? Autopilot disconnect warning? Marker Beacon? Altitude Alert?

P19 EDFE EDVE EDDS

just bumped into this old thread

Mooney_Driver wrote:

We just had an accident report published where a defective stall warning switch most probably caused a near ground stall condition which the pilot did not reckognize due to the lack of warning. He managed to crashland the plane and nobody was hurt but the plane was a write off.

I’ve been looking for this report but cannot find it. MD would you happen to have a reference where I could find it ?

EBTN, EBST, Belgium
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