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Comment by blattimwind | Hacker News Reader

I assume you can walk up to it and turn it by hand to at least see that the mechanical part is moving freely as-of now.

It can freeze from icing or other low temperature conditions after takeoff. The sensors are heated to prevent this, with a system in place to detect if the heater has failed, but they can still jam from a heater failure that is not detected or heavy icing.

Surely this could be easily detected, even with too low airspeed to give reliable readings the sensors should flap around slightly and thus provide noise. If they're frozen, there should be very little noise in comparison.

In addition you should be able to cross-correlate with gyro and airspeed sensor, not to check the absolute AoA, but certainly determine if delta-AoA is near zero (frozen) or not.

The sensors should be on good bearings, in order to promote them moving freely. Them flapping around slightly won't provide much noise. Which is probably drowned out by all the other noise on an aircraft.

> Them flapping around slightly won't provide much noise. Which is probably drowned out by all the other noise on an aircraft.

But the readings with the vane flapping around should have a significantly higher variance than the readings where the vane has frozen stuck. In addition, a sliding average should show the mean moving around significantly compared to the frozen readings. Surely they should be able to discriminate between these cases based on those factors, especially when cross-correlated with other sensors.

Can't always test the mechanics like that. Ex: Pitot tubes are just hollow tubes. The interiors of pitot tubes getting iced over has crashed planes. This wouldn't even be visible from the outside, and there is no test you could do.

Couldn’t you just blow in?

No. The tube leads to a pressure sensor. There's generally no actual airflow moving through the tube in use.

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