WannFly
Final Approach
background of my flights yesterday:
Before i took off yesterday, i read up on Cold temp restricted airports and as i understand its primarily for Instrument approaches with MDA, DA and other alphabet soups, however, i also read somewhere about computing that en-route and the logic is... your altimeter is showing you re at 5000 , in reality you are at 4600 -- that could lead to traffic separation problem and you should tell ATC so they know.
what i observed -- my altimeter was showing i was at 5500, my GPS Alt was showing i am at 4800 (usually its 200 ft off, but it was 700 ft off yesterday) and my Transponder was showing 5100. this is the first time i have seen such a discrepancy. usually the transponder is very close to the altimeter. it confused the heck out of me and i added 500 ft to my pattern altitude and ended up incredibly high on final (hello forward slip to land )
while coming back, i inquired approached as to what they are seeing as my altitude. they said 4200 ft, thats what my Altimeter was telling me, but my transponder was showing 3800 for Alt. I was under the impression ATC sees what my transponder tells them.. donno. may be because i was within TRSA and they have some other gizmo there...
so long story short... i am kinda confused with the temp correction rt now. if i am with Center and i tell them i was at 5500, i am thinking i better be with 100 ft of that, if nothing for traffic separation, another dude could be at 5000 cruising along looking at his iGizmo while i am happily cruising at 5100 ft in reality.
thoughts?
- surface temp at take off -23F, DA -5300
- OAT at 5500 MSL (roughly 4500 AGL) -14C while going, OAT -16C at 3900 MSL (roughly 2900 AGL)
- surface temp at landing -6F, DA -3600
Before i took off yesterday, i read up on Cold temp restricted airports and as i understand its primarily for Instrument approaches with MDA, DA and other alphabet soups, however, i also read somewhere about computing that en-route and the logic is... your altimeter is showing you re at 5000 , in reality you are at 4600 -- that could lead to traffic separation problem and you should tell ATC so they know.
what i observed -- my altimeter was showing i was at 5500, my GPS Alt was showing i am at 4800 (usually its 200 ft off, but it was 700 ft off yesterday) and my Transponder was showing 5100. this is the first time i have seen such a discrepancy. usually the transponder is very close to the altimeter. it confused the heck out of me and i added 500 ft to my pattern altitude and ended up incredibly high on final (hello forward slip to land )
while coming back, i inquired approached as to what they are seeing as my altitude. they said 4200 ft, thats what my Altimeter was telling me, but my transponder was showing 3800 for Alt. I was under the impression ATC sees what my transponder tells them.. donno. may be because i was within TRSA and they have some other gizmo there...
so long story short... i am kinda confused with the temp correction rt now. if i am with Center and i tell them i was at 5500, i am thinking i better be with 100 ft of that, if nothing for traffic separation, another dude could be at 5000 cruising along looking at his iGizmo while i am happily cruising at 5100 ft in reality.
thoughts?