Altitude is not known, as that varies wherever you are on Earth.... cept in a boat on the ocean I suppose. Aircraft altimeters are +/- 75 ft to meet spec, but are usually kept within 20 ft or so. The accuracy of an altimeter usually goes down as high altitudes are attained. Civilian altimeters are not necessarily more accurate than military - there are many types for many applications, but I digress. Back to GPS: One airplane I fly has an FAA approved GPS for instrument approaches. This connects to the aircraft's altimeter as part of an extravagant backup system - if the GPS measured altitude starts going haywire compared to the altimeter encoder's output, it signals the pilot that nav information isn't accurate enough for the instrument approach. I've seen this happen on about 1 out of every 10 approaches shot - I'm very curious to see how turning off SA will effect this. Also, when the GPS doens't work quite right for the approach, its not a big deal - we can always switch to a more archaic (and often more accurate) approach system designed 30+ years ago!!! Heck its even easier to use (this is coming from the mouth of a compute engineer) So much for new technology.
Slashdot Mirror
Altitude is not known, as that varies wherever you are on Earth.... cept in a boat on the ocean I suppose. Aircraft altimeters are +/- 75 ft to meet spec, but are usually kept within 20 ft or so. The accuracy of an altimeter usually goes down as high altitudes are attained. Civilian altimeters are not necessarily more accurate than military - there are many types for many applications, but I digress. Back to GPS: One airplane I fly has an FAA approved GPS for instrument approaches. This connects to the aircraft's altimeter as part of an extravagant backup system - if the GPS measured altitude starts going haywire compared to the altimeter encoder's output, it signals the pilot that nav information isn't accurate enough for the instrument approach. I've seen this happen on about 1 out of every 10 approaches shot - I'm very curious to see how turning off SA will effect this. Also, when the GPS doens't work quite right for the approach, its not a big deal - we can always switch to a more archaic (and often more accurate) approach system designed 30+ years ago!!! Heck its even easier to use (this is coming from the mouth of a compute engineer) So much for new technology.