Checking The Stall Warning Horn
When a pilot first glances at the title of this article, the first thought that probably goes through that pilot’s head is, well that’s easy.
And it is, if you are flying a high wing Cessna. On other airplanes, there are a few tricks to checking the stall warning horn. If you get them wrong, you’re liable to get a bill from your maintenance shop for an hour of labor for a problem they couldn’t duplicate.
Cirrus SR22
Let’s start with the Cirrus. On the pre-FIKI Cirrus aircraft, there was a small little hole in the wing that contained a diaphragm. That diaphragm sensed a change in airflow at a certain angle of attack just below the critical angle of attack and set off the stall warning horn. Unfortunately, the only way to check that is to suck on the hole during pre-flight.
I don’t. I verify the hole is clear and that’s about it.
On the FIKI Cirrus aircraft, there is actually a stall warning vane. It looks like a high wing Cessna vane, but if you turn the batteries on and try and get it to come on during your light and pitot heat check, nada.
Here’s the trick, and the checklist doesn’t do a good job of describing this.
- Turn on the Avionics Master
- Turn on the speaker
- Put the flaps to full
- Then move the stall warning vane and you’ll hear the horn
The speaker and the Avionics Master are so you can actually hear the horn (if you had the headset on while you were doing this, the speaker would be unnecessary). The flaps have to be full because the pitch attitude for the critical angle of attack is lower with the flaps down, so the horn goes off when at a different angle. You then don’t have to use as much force to push the vane.
Piper PA46
The early -310P Malibus are pretty simple and straight forward. Move the vane, get the horn.
In the -350P, you can’t get the horn to come on by moving the vane. So, Piper put a stall test button that’s hidden underneath the upper left side of the instrument panel. Push that to test the horn. On the G1000 PA46, it is located directly above the PFD. On the Avidyne, it’s below and to the left of the pilot’s yoke.
Testing the stall warning horn is a very important part of pre-flight. A pilot needs to know if the aircraft is close to a stall. The advent of Angle of Attack indicators in small, GA aircraft, have added a greater awareness to the angle of attack during all phases of flight to avoid those stall spins.
If the stall warning horn goes off or the AOA shows yellow, lower that nose immediately.
One thing that I learned this summer was this. Sometimes, with an area of closely grouped storms, the cloud base is actually quite high (some storms I went underneath in New Mexico had cloud bases of 15,000 MSL). The thing to do here is just stay below the bases of the clouds and go around the areas of rain. These will be visible and you’ll be able to navigate around them. With bases even as low 9-10 thousand feet, it’s a much better idea to stay below the clouds, sacrifice some speed, and dodge the rain shafts.
