[Info-vax] OT: Aircraft pitot tubes and clustering.

[Richard B. Gilbert]

David Mathog wrote:
> JF Mezei wrote:
> 
>> BUT, they found cases where 2 probes failed at the same time and by the
>> same magnitude. This caused the remaining one to be kicked out despite
>> being correct, and the 2 errorneous ones to be used because the
>> differences between them are within bounds. As a result, the aircraft
>> used very wrong values for the air sensors.
> 
> This could happen if the most common tube failure mode was to take the 
> output voltage to ground or supply voltage.  Then if two failed in the 
> way they are most likely to they will read exactly the same thing.
> Presumably the software should reject readings in these failure mode 
> voltage ranges out of hand, but it might not.
> 
> Regards,
> 
> David Mathog
> 

No voltage necessary in the case at hand.  At least in light aircraft 
the pitot (impact) pressure is used, in conjunction with the static 
pressure, to determine the airspeed.  It can be done with nothing but 
plumbing and a pressure gage.  AFAIK this approach is used in most aircraft.

The pitot tube and the static pressure port are both things the the wise 
pilot checks as part of his preflight inspection.