My headset is an altimeter.

dcat127

dcat127

Pre-Flight
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Jun 30, 2020
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Electro
I have a light speed sierra headset that has recently started giving high pitched squeal in the one ear at certain altitudes. Yesterday on a cross country flight with 3 takeoffs and landings it did it each time from both in the climb and decent exactly 4200 feet till 4600. It stops when I turn the headset off, so I'm fairly sure it is the anc circuitry that is causing feedback.

What is possibly in the circuitry that could cause this?
 
Open window or air vent?
 
I’ve started getting this in my almost 4 year old A20s. I suspect my ear cups are losing seal and letting extra sound in.
 
Is your vox set too low?
 
I dont't think is a vent I tried it both open and closed, no difference.

Nor do I think it is the earcups. The squeal is so loud it is unbearable, I completely removed the headset, their was no change in pitch or volume when breaking the earpiece seal.

I'm fairly sure it it not related to the radio/intercom, as it is only the one ear.
 
Further none of these ideas give any reason that would be altitude related...
 
That's weird. Temperature dependent intermittent problems with electronic equipment is common, and mechanical intermittents, too. I've never heard of altitude dependent, but I can't see why it's not possible. For mechanical, it can be broken/cold solder joints, or I believe problems with the bonding wires inside ICs. Same thing for thermal. Dielectric constant of air changes with altitude I believe, and breakdown voltage in air, but 4200' isn't very high.

My engineering but not avionics background says that you have a circuit in there that barely works and really wants to oscillate, and that whatever minor physical change happens to the sealed parts at that altitude it causing it to oscillate. If it were mine, I'd probably try taking the electronics out of the packaging and heat them up with an air iron at a very low temp, until it started oscillating or died, and then fix it. But that route may just fully break whatever is now intermittent, and it might not find the root problem. My bet would be an IC, discreet transistor if there are any, or a capacitor acting weird.
 
We had a set of Sierras doing that at work that would do it intermittently but on the ground and at 13.5k ft unpressurized. It is a short, evidently.
 
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