Altimeter issues. Reset/Calibration possible?

[Psignore00]

I thought of this discussion when reading this article about the aircraft’s altimeter readings being 100 ft different at the time of the crash. I’m no conspiracy theorist, but might this be explained the same way as our altimeters in the Grenadier are off by 100 feet at times?

Data from the collision of the airliner and Army helicopter show a 100-foot difference in altitude

Data from the jet’s flight recorder showed its altitude as 325 feet, plus or minus 25 feet, when the crash happened. Data in the control tower showed the helicopter at 200 feet.

fortune.com

 

[Ovrland Bill]

I thought of this discussion when reading this article about the aircraft’s altimeter readings being 100 ft different at the time of the crash. I’m no conspiracy theorist, but might this be explained the same way as our altimeters in the Grenadier are off by 100 feet at times?

Data from the collision of the airliner and Army helicopter show a 100-foot difference in altitude

Data from the jet’s flight recorder showed its altitude as 325 feet, plus or minus 25 feet, when the crash happened. Data in the control tower showed the helicopter at 200 feet.

fortune.com

I suspect that a difference in the Controller’s display readout in the Tower Cab may be more a matter of latency in updating the information.

 

[Clark Kent]

I thought of this discussion when reading this article about the aircraft’s altimeter readings being 100 ft different at the time of the crash. I’m no conspiracy theorist, but might this be explained the same way as our altimeters in the Grenadier are off by 100 feet at times?

Data from the collision of the airliner and Army helicopter show a 100-foot difference in altitude

Data from the jet’s flight recorder showed its altitude as 325 feet, plus or minus 25 feet, when the crash happened. Data in the control tower showed the helicopter at 200 feet.

fortune.com

Good question.

At 200' above the river the Blackhawk crew were possibly using a radio altimeter (radalt) for vertical reference, i.e. height above the ground. Radalt uses a timed radio signal underneath the aircraft that bounces off the ground to report height. Radalt is far more accurate at low level than a static pressure (barometric) altimeter but does have some drawbacks.

ATC gets aircraft altitude information from a few different sources including mode C data encoding through the Identification Friend or Foe (IFF) transponder system. I don't know the UH60M at all and it's been 25 years since I trained on UH60A (actually, the S70A export version). I cannot recall if radalt data is encoded as IFF mode C - if the radalt is in use - or if only pressure altitude is used for mode C. Someone more current than me will know the answer so please jump in.

It's been asked before but not answered conclusively: Does the altitude display in the Grenadier compass use data derived from the GPS or is it using air pressure like a barometer? My gut says it's GPS-derived because the compass heading and altitude display for Australia and South Africa market MY23 vehicles was freezing due to a GPS satellite signal timing error. The compass came good after a software update.

My theory becomes less certain when we see day to day variation in altitude for the same location. This could be due to a local barometric pressure change or a GPS triangulation error if there are minimal satellites in view.

 

[anand]

It's been asked before but not answered conclusively: Does the altitude display in the Grenadier compass use data derived from the GPS or is it using air pressure like a barometer? My gut says it's GPS-derived because the compass heading and altitude display for Australia and South Africa market MY23 vehicles was freezing due to a GPS satellite signal timing error. The compass came good after a software update.

My theory becomes less certain when we see day to day variation in altitude for the same location. This could be due to a local barometric pressure change or a GPS triangulation error if there are minimal satellites in view.

GPS derived with a +/- 100ft variance; and from at least one internal source

 

[Clark Kent]

GPS derived with a +/- 100ft variance; and from at least one internal source

That explains the variation. Thanks @anand

 

[Ovrland Bill]

Good question.

At 200' above the river the Blackhawk crew were possibly using a radio altimeter (radalt) for vertical reference, i.e. height above the ground. Radalt uses a timed radio signal underneath the aircraft that bounces off the ground to report height. Radalt is far more accurate at low level than a static pressure (barometric) altimeter but does have some drawbacks.

ATC gets aircraft altitude information from a few different sources including mode C data encoding through the Identification Friend or Foe (IFF) transponder system. I don't know the UH60M at all and it's been 25 years since I trained on UH60A (actually, the S70A export version). I cannot recall if radalt data is encoded as IFF mode C - if the radalt is in use - or if only pressure altitude is used for mode C. Someone more current than me will know the answer so please jump in.

It's been asked before but not answered conclusively: Does the altitude display in the Grenadier compass use data derived from the GPS or is it using air pressure like a barometer? My gut says it's GPS-derived because the compass heading and altitude display for Australia and South Africa market MY23 vehicles was freezing due to a GPS satellite signal timing error. The compass came good after a software update.

My theory becomes less certain when we see day to day variation in altitude for the same location. This could be due to a local barometric pressure change or a GPS triangulation error if there are minimal satellites in view.

The Transponder Mode C that I used in 2013 reported only QNE “Pressure Altitude” (referenced to 29.92” or 1013 mb of Hg). The local altimeter setting in use was then applied AFTER THE REPORT WAS RECEIVED in order to convert QNE to QNH Altitude (Mean Sea Level reference).

 

[Jiman01]

After seeing this thread, I checked my altimeter/compass and found that my compass is 180° off. Basically north is south and south is north….

I’m assuming the compass is electronic versus magnetic so it can’t be that it got magnetized somehow.

 

[anand]

After seeing this thread, I checked my altimeter/compass and found that my compass is 180° off. Basically north is south and south is north….

I’m assuming the compass is electronic versus magnetic so it can’t be that it got magnetized somehow.

Did you check this after driving around a bit? As stupid as this sounds, make sure you didn't back into a parking spot

 

[Jiman01]

Did you check this after driving around a bit? As stupid as this sounds, make sure you didn't back into a parking spot

I noticed it after start up at home when the compass spins and settles. I actually never even noticed that it did that cause I’m too occupied turning off ADAS and connecting my phone

By the time I got on the road, I forgot about it and never bothered to check. I’ll try and remember next time