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On Jan 7, 2005, at 12:50 PM, Ed Burkhead wrote: > Frank, > > For altimeter checking, I never did anything more than dial in the > altimeter setting and compare it to field altitude. A couple of times > I > flew by tall antennas as a cross check. If there's more required, I > really don't know what. > As a Weather Observer in the Air Force in the early sixties, we took routine hourly "observations" of the weather. These were taken approximately ten minutes before the hour to allow for preparation and transmission by teletype, and the local barometric pressure was noted at that time. The tower would get the newest information on the hour. For the next hour this information was relayed by controllers to pilots as the "current altimeter setting", even though, by the end of the hour, it was anything but current. A pilot would "set" his altimeter by dialing this value into his instrument and all was presumably as it should be. In the real world, barometric pressure changes minute to minute, particularly following a strong frontal passage. The pilot of an airplane running up next to the field elevation sign a few minutes before the hour could see a significant difference in indicated elevation that he was expected to ignore. Like Ed, I set to field elevation before takeoff; knowing THAT is currently accurate information, official or not. Over time, altimeters can lose their calibration. The FAA clearly does not deem a mere pilot smart enough to turn the calibration screw on the face of this instrument now and then so that a FRESH "official" altimeter setting and the field elevation on the sign stay reasonably in agreement. I think our A&P or IA is supposed to check to see if our altimeter is within allowable variation at each annual. If it isn't that becomes a squawk requiring the ministrations of an FAA-certificated instrument technician. He turns the screw under standard conditions at a considerable hourly rate or minimum charge, plus shipping, while our flying machine sits on the tarmac rendered unairworthy by the missing instrument. A pilot can't totally ignore "official" altimeter settings, because they may pass through different air masses enroute on longer flights. If he/she suspects a pressure change of significance, a call to an appropriate tower or FSS along the route will allow inflight resetting of the altimeter to more current(?) and local information. Regards, WRB ========================================================================== ==== To leave this forum go to: http://ercoupers.com/lists.htm Search the archives on http://escribe.com/aviation/coupers-tech/
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