Inop Stall Warning

[rpadula]

I got into an interesting discussion with a friend about whether it was legal to fly VFR or IFR with an inoperative stall warning horn. Device is a switch on leading edge of wing, and when pressed up, did not produce the warning (master and avoinics power were on).

We couldn't really come up with a final answer. So far:

1. Stall warning not required for VFR or IFR flights per 91.205 (a)-(d).

2. Probably falls under 91.213 - Inoperative Instruments and equipment.


Our questions about 91.213:

1. How does one determine the minimum equipment list required by 91.213(a) and (b)? There's nothing in the plane's flight manual with that title, just a section on "Systems" which includes one paragraph on the stall warning system.

2. If there is no MEL, then it looks like 91.213(d) applies. How would one determine if the stall warning was part of the type certificate, as in 91.213(d)(2)(i)? Would it be in the Type Certificate Data Sheet?

3. How would one placard this? There's no "cockpit control" for a stall warning buzzer.

Am I missing anything else?


-Rich

 

[BruceAir]

You may find the following information helpful. Note the links at the bottom of the excerpt of the full article:

http://www.awp.faa.gov/fsdo/ans_oct_97.htm

 

[Ed Guthrie]

We couldn't really come up with a final answer.

Piece of cake--99.9999% probability that the aircraft is not airworthy. The only thing left to determine is which piece of paper will support that obvious conclusion.

So far:

2. Probably falls under 91.213 - Inoperative Instruments and equipment.

Definitely.

Our questions about 91.213:

1. How does one determine the minimum equipment list required by 91.213(a) and (b)? There's nothing in the plane's flight manual with that title, just a section on "Systems" which includes one paragraph on the stall warning system.

The aircraft will have an equipment list in the POH and/or in the TCDS which will specify equipment required for flight. The POH list would be in "Weight & Balance" under "Equipment". Look at the front of the list for the notations as to required or optional. For example, a Cessna uses "R" for required, "S" for standard (not required), "O" for optional item replacing an "S" item, and one other letter which escapes me right now (I'm a long way from my library this week). However, unless you either have an MEL for the aircraft (highly doubtful) or are creating one (a) & (b) don't apply to this situation.

2. If there is no MEL,

Unless you or a previous owner created one for that specific aircraft serial number this is another 99.9999% probability--there is no MEL for this aircraft.

then it looks like 91.213(d) applies. How would one determine if the stall warning was part of the type certificate, as in 91.213(d)(2)(i)? Would it be in the Type Certificate Data Sheet?

Probably, or the POH, or most likely both.

3. How would one placard this? There's no "cockpit control" for a stall warning buzzer.

Assuming the stall warning horn isn't an "R" item (99.9999% probability that it is an "R" item) you would disable the circuit (most folks pull the breaker and wrap a nylon ty-wrap around the stem to prevent someone from resetting the breaker) and you would put a placard on the panel in very obvious sight of the pilot stating "STALL WARNING HORN INOP" or some such.

Am I missing anything else?

Only the point in the aircraft documentation where you will find that the stall warning horn is required equipment. If you post what aircraft make/model I'm sure folks here could find the notation for you.

 

[poadeleted20]

And if you can't find an equipment list or MEL for the plane, EVERYTHING is required unless you can prove otherwise by getting further information from the type certificate holder, since without that list, you don't know what was required for type certification.

 

[poadeleted20]

1. Stall warning not required for VFR or IFR flights per 91.205 (a)-(d).

2. Probably falls under 91.213 - Inoperative Instruments and equipment.

Agreed.

1. How does one determine the minimum equipment list required by 91.213(a) and (b)? There's nothing in the plane's flight manual with that title, just a section on "Systems" which includes one paragraph on the stall warning system.

Check Section 6 - Weight & Balance/Equipment List. If you don't have that, you should refer to the original equipment list that was provided by the factory. If that's gone, contact the type certificate holder, as these are kept on file.

2. If there is no MEL, then it looks like 91.213(d) applies. How would one determine if the stall warning was part of the type certificate, as in 91.213(d)(2)(i)? Would it be in the Type Certificate Data Sheet?

It might be on the TCDS, but probably not. In that case, you have to contact the type certificate holder or the FAA Aircraft Certification Office covering this type.

3. How would one placard this? There's no "cockpit control" for a stall warning buzzer.

Perhaps a bit "STALL WARNING INOP" sticker next to the ASI.

 

[rpadula]

Okay, this is for a Commander 112A.

After digging around in the big bag o' paperwork, I found a folder labeled Equipment List, Aero Commander 112A. Making progress....

The equipment list begins with "Standard Equipment" items, and then moves on to "Optional Equipment." Under Standard Equipment, Electrical Equipment subheading, there are Stall Warning Horn and Lift Detector (which I presume is the switch on the wing). The word "required" isn't anywhere in these pages, although I assume since standard equipment also includes the engine and the prop, standard equipment is pretty darned important.

 

[poadeleted20]

The equipment list begins with "Standard Equipment" items, and then moves on to "Optional Equipment." Under Standard Equipment, Electrical Equipment subheading, there are Stall Warning Horn and Lift Detector (which I presume is the switch on the wing). The word "required" isn't anywhere in these pages

Argghhh. Looks like you're going to have to ask either Commander Aircraft or the ACO covering them. But I wouldn't fly with it inop until you get this resolved, as the FAA's general position is that ignorance is no excuse.

 

[rpadula]

Thanks Ron. That might be easier said than done given the bankruptcy stuff going on at Commander right now.

There may be hope -- the guys at the Commander board say some Commanders have a bypass/test switch in the wheel well. The guy I bought it from is out of town, but I'll try to ask him if there are any special gyrations needed to test this.

Now, why did I buy this thing again?


-Rich

 

[rpadula]

Inop Stall Warning Solved

Now, why did I buy this thing again?

Oh yeah, because I'll get to fly it!

Problem solved. According to my mechanic, the stall horn is quite voltage sensitive, which he found to be the case during the annual.

He handed me some masking tape and said tape the switch up then start the engine to raise the voltage. So I taped it up and as soon as I hit the master switch, "Blahhhhhh!" right in my ear!

What I had done before was turn on the master, turn on the avionics master in case it was tied to that bus (it wasn't, but the extra load from the radios made a nice voltage drop) and then hoof it around to the front of the wing to lift the leaf switch. By then, the voltage was too low to sound the alarm.

Weird but true.


Thanks for all the help...


-Rich

 

[wsuffa]

Re: Inop Stall Warning Solved

Oh yeah, because I'll get to fly it!

Problem solved. According to my mechanic, the stall horn is quite voltage sensitive, which he found to be the case during the annual.

He handed me some masking tape and said tape the switch up then start the engine to raise the voltage. So I taped it up and as soon as I hit the master switch, "Blahhhhhh!" right in my ear!

What I had done before was turn on the master, turn on the avionics master in case it was tied to that bus (it wasn't, but the extra load from the radios made a nice voltage drop) and then hoof it around to the front of the wing to lift the leaf switch. By then, the voltage was too low to sound the alarm.

Weird but true.


Thanks for all the help...


-Rich

Rich, something is wrong. Either you have a problem in the electrical system or the stall waraning system. It's really not sensitive to voltage. Does your plane have the test switch in the wheel well in addition to the leaf switch?

 

[gismo]

Re: Inop Stall Warning Solved

Rich, something is wrong. Either you have a problem in the electrical system or the stall waraning system. It's really not sensitive to voltage. Does your plane have the test switch in the wheel well in addition to the leaf switch?

I agree. Most of the stall horns are nothing more than an old electric bicycle horn which is basically a buzzer connected to a diaphram. It should be able to sound with as little as 6-8 volts. It could be that the "buzzer" contacts are corroded/pitted, or there could be excessive resistance in the circuit (switch, wiring, connectors).

Also if your battery voltage drops fast with the master on, the battery needs replacing. Otherwise you'll have about 3 minutes of power if the alternator fails in flight.

 

[wsuffa]

I'd be betting a bad ground somewhere in the stall warning circuit. Or a bad circuit breaker or wire.

That stall vane is a microswitch. It drives a buzzer. For some of the Commanders there is a test switch in the wheel well. The circuit is really simple.