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#1
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Altimeter accuracy
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. |
#2
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Altimeter accuracy
75'
"Jim Stewart" wrote in message ... 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. |
#3
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Altimeter accuracy
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 |
#4
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Altimeter accuracy
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 |
#5
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Altimeter accuracy
"Jim Stewart" wrote in message
... 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. What's the accuracy of the AWOS? -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. |
#6
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Altimeter accuracy
Capt. Geoffrey Thorpe wrote:
"Jim Stewart" wrote in message ... 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. What's the accuracy of the AWOS? Glad you asked. I called some friends at Allweather (which made the AWOS at my field) and they said the units are factory calibrated to +/- 5 feet and that FAA specifications are +/- 20 feet. -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. |
#7
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Altimeter accuracy
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 |
#8
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Altimeter accuracy
On Mon, 07 May 2007 20:41:13 GMT, "Jim Carter"
wrote: 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? I did cite the bench testing numbers, as they are the ones of which I am aware. I've heard of the 75' "allowance" for a field measurement, but I've not seen a regulatory justification for that value. As someone who flies instrument approaches to minimums, I, personally, would not be happy with a 75' error, and would have the system rechecked. So far as you being only 105' off the deck in your hypothetical instance, that is obviously the case. By the way, for Category II operations, which may have a DH as low as 100'AGL, it is a requirement to have readily available the altimeter calibration information from the last certification, (and to apply it appropriately). --ron |
#9
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Altimeter accuracy
Isn't a radar altimeter required equipment for CAT II and CAT III work? We
were trying to get an aircraft and aircrew certified for CAT II in Seattle many years ago and I thought that was the reason they had the RA installed. -- Jim Carter Rogers, Arkansas "Ron Rosenfeld" wrote in message ... On Mon, 07 May 2007 20:41:13 GMT, "Jim Carter" wrote: 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? I did cite the bench testing numbers, as they are the ones of which I am aware. I've heard of the 75' "allowance" for a field measurement, but I've not seen a regulatory justification for that value. As someone who flies instrument approaches to minimums, I, personally, would not be happy with a 75' error, and would have the system rechecked. So far as you being only 105' off the deck in your hypothetical instance, that is obviously the case. By the way, for Category II operations, which may have a DH as low as 100'AGL, it is a requirement to have readily available the altimeter calibration information from the last certification, (and to apply it appropriately). --ron |
#10
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Altimeter accuracy
I read somewhere on the web that your A&P can adjust your altimeter by
removing a pin or a screw that allows the barometric pressure to be set independently from the altitude. Once it's set correctly, the pin or screw is replaced. Dave 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. |
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