Flight following

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landon18

Pre-Flight
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Feb 25, 2023
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Landon Scarbrough
Hey guys, I’m readily use flight following. When I’m checking in the first time to obtain flight following they show me a higher altitude than I am and it happens Multiple times recently. Is this on their end or on my end because my phone and FlightAware and ForeFlight say what my altimeter says
 
Assuming you’re changing your alt setting each handoff, yeah, something doesn’t sound right.
 
landon18 said:
Hey guys, I’m readily use flight following. When I’m checking in the first time to obtain flight following they show me a higher altitude than I am and it happens Multiple times recently. Is this on their end or on my end because my phone and FlightAware and ForeFlight say what my altimeter says
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Same here. By 200 ft. Weird.
 
landon18 said:
Hey guys, I’m readily use flight following. When I’m checking in the first time to obtain flight following they show me a higher altitude than I am and it happens Multiple times recently. Is this on their end or on my end because my phone and FlightAware and ForeFlight say what my altimeter says
Click to expand...
In a VFR airplane, the transponder must be checked each 24 months, when was the last time it was tested? Was the altimeter tested at that time?
 
FlightAware doesn't matter. What matters is what ATC radar is seeing, which comes from your encoder. If it is more than 300 feet different from what your altimeter is telling you, expect to hear "stop squawking Mode C" which means turn off the ALT feature on your transponder, and report your altitude to ATC when asked or when changing frequencies (which you should do anyway).

Ask your avionics guy to test your encoder. It is not uncommon for them to be a bit out of whack.
 
Gilbert Buettner said:
FlightAware doesn't matter. What matters is what ATC radar is seeing, which comes from your encoder. If it is more than 300 feet different from what your altimeter is telling you, expect to hear "stop squawking Mode C" which means turn off the ALT feature on your transponder, and report your altitude to ATC when asked or when changing frequencies (which you should do anyway).

Ask your avionics guy to test your encoder. It is not uncommon for them to be a bit out of whack.
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Yes don’t believe it was above 300 ft
 
+1 vote for check your encoder.
I had a leaky encoder for a little bit and it caused the exact same problem. Never exceeded 300', but 1-200' delta was normal for the short period it was broken.
Replacing the broken encoder fixed everything.
 
ArrowFlyer86 said:
+1 vote for check your encoder.
I had a leaky encoder for a little bit and it caused the exact same problem. Never exceeded 300', but 1-200' delta was normal for the short period it was broken.
Replacing the broken encoder fixed everything.
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Ok thank you
 
landon18 said:
Hey guys, I’m readily use flight following. When I’m checking in the first time to obtain flight following they show me a higher altitude than I am and it happens Multiple times recently. Is this on their end or on my end because my phone and FlightAware and ForeFlight say what my altimeter says
Click to expand...
Your phone, FlightAware, and ForeFlight should not normally match what your altimeter says. Your altimeter is MSL when you have the correct altimeter setting entered. FlightAware is pressure altitude, which is standard pressure with the altimeter set to 29.92. Depending on if you have a device such as Sentry that provides a pressure altitude based on the cabin pressure, ForeFlight will show a Baro Altitude that may match what your ship's altimeter reads, but the cabin altitude is often off the true pressure altitude by 100 to 200 feet, since it is not tied into the aircraft static source. If you don't have a pressure altitude source, ForeFlight will show GPS altitude which can be expected to roughly match what your ship's altimeter shows when temperatures are standard, but when not standard they can easily differ by 500 feet or more.

As others have indicated, your transponder and your ADS-B Out typically use a blind encoder to determine the pressure altitude and transmit that value to the ATC secondary radar or ADS-B ground station. Many blind encoders are only precise to 100 feet. ATC software converts the pressure altitude to an MSL altitude for display to the controller.
 
John Collins said:
Your phone, FlightAware, and ForeFlight should not normally match what your altimeter says. Your altimeter is MSL when you have the correct altimeter setting entered. FlightAware is pressure altitude, which is standard pressure with the altimeter set to 29.92. Depending on if you have a device such as Sentry that provides a pressure altitude based on the cabin pressure, ForeFlight will show a Baro Altitude that may match what your ship's altimeter reads, but the cabin altitude is often off the true pressure altitude by 100 to 200 feet, since it is not tied into the aircraft static source. If you don't have a pressure altitude source, ForeFlight will show GPS altitude which can be expected to roughly match what your ship's altimeter shows when temperatures are standard, but when not standard they can easily differ by 500 feet or more.

As others have indicated, your transponder and your ADS-B Out typically use a blind encoder to determine the pressure altitude and transmit that value to the ATC secondary radar or ADS-B ground station. Many blind encoders are only precise to 100 feet. ATC software converts the pressure altitude to an MSL altitude for display to the controller.
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Ok so I guess I probably shouldn’t worry about it
 
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