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Instant OAT jmp

RV8iator

Well Known Member
Benefactor
Fishing for ideas before changing my GRT OAT probe.
I was happily cruising along at 10,500 coming home Saturday afternoon and was actually looking at my EFIS, a GRT HXr, and as I was looking at the OAT it instantly doubled from 63 to 126 degrees. True airspeed jumped from 173 to 186 kts.
Anybody ever seen this type of failure mode or have any ideas?
 
Could be way out into left field here if you are referring to TAS changing it was maybe due to the OAT going wacky and screwing up the internal TAS calculations within the EFIS??
 
Could be way out into left field here if you are referring to TAS changing it was maybe due to the OAT going wacky and screwing up the internal TAS calculations within the EFIS??

Yeah. I know the OAT messed up the TAS and wind calcs. I’m wondering if anybody had had a doubling of the OAT indication and what the failure may be caused by.
 
Are you running the probe to the EIS or direct to the EFIS?
While the exact doubling looks strange, I’ll bet 126 is an upper software limit. I’d measure the probe looking for an open circuit.
 
Most logical scenario is that sensor lost ground connectiion. This could be the the wire going from sensor to airframe ground or the wire on the thermistor inside the alum housing separated. Should be easy to assess with an ohm meter.

Ask GRT if 126 is max resistance or no resistance, assuming like bob that is the end of the range. The former would be an open on the sensor or ground line or in the sensor itself. The later would be a short to ground on the sensor feed line or in the sensor itself.

Larry
 
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