GPS Altitude with WAAS

But think for a second - why do you suppose MEA's and OROCA's provide
1000 ft of obstacle clearace normally, but 2000 in designated
mountainlous areas? If you're IFR, you're not going to be clearing
that peak by less than 2000 ft, and that is going to keep you out of
the rocks in even the worst case scenario. If you're VFR, then you
can see the peak and don't really need the altimeter anyway.


I don't buy it. On a good weather day in California it is not uncommon
for the alimeter setting itself to account for 500 ft altimeter errors
in the mountains. If you add up non-standard lapse rate, cold air and
old and distant altimeter settings you can eat into the 2000 feet rather
quickly. Then deal with turbulent air and downdrafts in the mountains
on top of this. I don't like it one bit.

Go land on a 2000 foot runway and tell me that's plenty of room between
a little airplane with poor climb performance and a big mountain that
you can't see.

"Michael" wrote in message
om...
Let's not forget that the
worst case temperature error at 200 ft and -50C is only 60 ft, while
altimeters can be up to 75 ft off in some cases and still be legal for
IFR use. There used to be a DH penalty for an inop middle marker
(either at the transmitter or receiver end) but this penalty no longer
applies. All this ignores the possibility that the pilost has a RADAR
altimeter available.

In the US, it is up to the pilot to decide whether in his particular
situation, given the available equipment and his skills, he should
adjust the minima as appropriate based on the expected temperature
error.

Michael

I've never seen, nor heard of a temperatures of -68F (at low airport-type
altitudes) that was not associated with an inversion. I suppose that it
might happen in Anarctica in the winter but there aren't any airports there.
In Alaska, when its -40F on the surface it is usually at least 0F at 1000'
AGL.

Mike
MU-2

I'm sure that in this case you are referring to the ICAO Cold
Temperature Error Table, which is part of the AIM. Check it out
online:
http://www1.faa.gov/ATPubs/AIM/Chap7/aim0702.html#7-2-3

I don't know about you, but I have yet to meet a US flight instructor
who does not require his students to have a copy of the AIM and be
conversant with it.

Uh. That table only showed up a couple of years ago. I bet most flight
instructors have no idea its even there. Other than "hot to cold look
out below" there ain't much on temperature errors in the FAA private
pilot knowledge requirements. The reason that table finally showed up
is because pilots familiar with Canadian and USAF procedures have been
pushing the FAA to improve this area of pilot knowledge.

We are not REQUIRED to do anything about those tables.

If you're flying over mountains in Alaska on a cold night with an
alitimeter setting from sea level? You can tell that to the granite.