I think what you've cited is for bench testing during certification. Once
installed in the aircraft then comparison against the pressure as recorded
by the official weather observation is +/- 75'.

An interesting discussion point came up recently that exposed the difference
in teaching over the past 30 years. 30 years ago we were taught to set the
altimeter to the known field elevation and record the difference between the
official pressure and the indicated pressure, then apply that difference to
every setting you received along your route of flight.

Today they teach to set your altimeter to the official pressure and that's
it.

So my question becomes, when executing a precision approach to a minimum DH
of 200' and then executing the missed procedure, the aircraft is allowed to
descend slightly below the DH as things spool up. If you are already 75'
lower than you think because of altimeter error, and you descend only 20'
more (one gradient on the altimeter) aren't you really only 105' off the
deck?


--
Jim Carter
Rogers, Arkansas
"Ron Rosenfeld" wrote in message
...
On Fri, 04 May 2007 01:42:07 GMT, Rip wrote:

Jim Stewart wrote:
How close should an altimeter be to field elevation
when set to the pressure indicated by the field's
AWOS? I'm seeing a 50' error.
+/- 75 feet for IFR

Rip

It depends on your field elevation.

You should be able to check and see what the error was at the last
altimeter certification for IFR.

The tolerances, at the lower altitudes, a (Appendix E 14 CFR 43)

0 ±20'
500 ±20'
1000 ±20'
1500 ±25'
2000 ±30'
3000 ±30
4000 ±35
6000 ±40
8000 ±60

For a VFR only a/c, I do not believe there is any particular requirement.
--ron