REFLECTOR: Static port calibration

Wed Mar 4 13:18:51 CST 2009

These are good methods for verifying altimeter. The easiest (with "0"
error) is to use the altitude at the departure end of a runway. It is a
known number and on the approach plate for that runway (should be done prior
to any (IFR) departure).

Larry Epstein

  GPS altitude.  Before folks get excited and say that GPS altitude can be
+- 100 feet remember "can be" but rarely is.  Every time I fly as part of my
instrument check I do a three way altitude check.  At the hold short line
for runway 18 at OJC my altitude is exactly 1100 feet.  I check my aneroid
altimeter and GPS altitude against this benchmark.  I almost never see a
difference of more than 20 feet on either altitude.  The aneroid and GPS
also track on cross country flights.  When I notice a difference I check a
local ATIS or AWOS and reset my colesman to the local barometer and they
again sync up.  A WAAS enabled GPS will typically show altitude to within 3
meters with a clear sky view.

Try it, you'll like it.

Larry Coen

N136LC

From: Al Gietzen <mailto:ALVentures at cox.net>  

Sent: Wednesday, March 04, 2009 9:40 AM

To: reflector <mailto:reflector at tvbf.org>  

Subject: REFLECTOR: Static port calibration

Out playing in the sky yesterday, I decided to do checks on altitude and
speed readings.  I had never done the 'low pass over the runway' test.  150
KIAS, est 80 ft over the runway, altimeter readout on the GRT EFIS was maybe
100 ft too high.  Hum-m-m.  

Went out and flew the orthogonal square about the same speed; recording GPS
ground speed and IAS in each direction, then took the average of each.  The
speeds agreed within 1.2 knots.

I've always found my altitudes consistent with where ATC says I am - so I
don't think I need to change anything.

Al

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