Light aircraft static altimeter max permisible tolerance on ground?
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Light aircraft static altimeter max permisible tolerance on ground?
I am after a definitive answer to a dispute that I have running with the guy who runs my flying group, if anyone could possibly help?
Both altimeters were under reading by 100ft on the ground before the aircraft went into a recent annual and C of A, it has came out the same, still under reading by 100ft on the ground. (surely this a should be calibrated as a matter of course during C of A regardless of me asking especially for it to be done??)
I asked for the altimeters to be calibrated as I feel that they are too far out. I was under the understanding that anymore than 50 or 60ft is unacceptable and am not at all happy that they are in error by 100ft.
The guy who runs the group, "in his opinion" (not an engineer by any stretch of the imagination!) sees this 100ft deviation as perfectly acceptable and he will not contact the maintenance company to determine if they have calibrated the altimeters nor will he put the aircraft back in to have it looked at as it does not see it necessary.
I have emailed CAA SRG (no reply!) to see what is the max permissible tolerance for a light aircraft altimeter so I can add fact / regulation to my argument.
I am the only guy in the group that is certified to fly IFR and the group runner feels that it is ok for him and other members to fly around VFR with 100ft under read on the altimeter. I don't feel that anymore that 50 or 60ft is acceptable.
The error of 100ft on the ground will increase with altitude and become more of a problem with separation etc at higher levels.
Any comments on this would be very much appreciated, along with possibly a technical doc / article / web link to support what tolerance is acceptable as per regulations
Both altimeters were under reading by 100ft on the ground before the aircraft went into a recent annual and C of A, it has came out the same, still under reading by 100ft on the ground. (surely this a should be calibrated as a matter of course during C of A regardless of me asking especially for it to be done??)
I asked for the altimeters to be calibrated as I feel that they are too far out. I was under the understanding that anymore than 50 or 60ft is unacceptable and am not at all happy that they are in error by 100ft.
The guy who runs the group, "in his opinion" (not an engineer by any stretch of the imagination!) sees this 100ft deviation as perfectly acceptable and he will not contact the maintenance company to determine if they have calibrated the altimeters nor will he put the aircraft back in to have it looked at as it does not see it necessary.
I have emailed CAA SRG (no reply!) to see what is the max permissible tolerance for a light aircraft altimeter so I can add fact / regulation to my argument.
I am the only guy in the group that is certified to fly IFR and the group runner feels that it is ok for him and other members to fly around VFR with 100ft under read on the altimeter. I don't feel that anymore that 50 or 60ft is acceptable.
The error of 100ft on the ground will increase with altitude and become more of a problem with separation etc at higher levels.
Any comments on this would be very much appreciated, along with possibly a technical doc / article / web link to support what tolerance is acceptable as per regulations
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Hi Capt,
Though Canadian, this standard should give you a starting point....
http://www.tc.gc.ca/civilaviation/Re...rds/a571sb.htm
Try Table 1
There should be a corresponding table referenced in your local authority's maintenance standards. Your maintenance facility should be easily able to find it.
Cheers, Pilot DAR
Though Canadian, this standard should give you a starting point....
http://www.tc.gc.ca/civilaviation/Re...rds/a571sb.htm
Try Table 1
There should be a corresponding table referenced in your local authority's maintenance standards. Your maintenance facility should be easily able to find it.
Cheers, Pilot DAR
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Under FAR Part 43 (basically, private flight of N-reg planes) the max allowed error is
1000ft or below - 20ft
1500ft - 25ft
2000-3999ft - 30ft
4000ft - 35ft
6000ft - 40ft
8000ft - 60ft
10000ft - 80ft
12000ft - 90ft
14000ft - 100ft
etc
1000ft or below - 20ft
1500ft - 25ft
2000-3999ft - 30ft
4000ft - 35ft
6000ft - 40ft
8000ft - 60ft
10000ft - 80ft
12000ft - 90ft
14000ft - 100ft
etc
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The common accepted error is 50ft and for IFR they must be with 50ft of each other.
Mine are calibrated every annual and rarely exceed a few of feet deviation from each other and the reference height.
But unless the aicraft is being used for IFR then I would not be worried about 100ft. You can see out the window can't you!
Mine are calibrated every annual and rarely exceed a few of feet deviation from each other and the reference height.
But unless the aicraft is being used for IFR then I would not be worried about 100ft. You can see out the window can't you!
What type of aircraft is it?
Most flight manuals on PA38/PA28 type aircraft list the max pressure error correction as plus or minus 50 ft.
That said there are other factors. The Altimeter check should always be done on QNH whilst parked on the apron. Apron elevations are listed in the UK AIP for major UK aerodromes. Without listing all the arguments if you are using QFE there may be other "errors" as you may or may not be using a threshold QFE or aerodrome QFE and not at the "reference" point.
Also when the pressure is measured it is always corrected down to the nearest millibar. E.g measured pressure 1000.9 mb, pilot is passed 1000 mb - in extremis this means a .9 mb error which equals 25 ft (1 mb = 27.3 ft). Hence the quoted of limits of -75/+50 ft (the extra 25 ft on the negative side to cater for the possible .9 mb difference).
If you have more than one altimeter then EACH altimeter should be within the tolerance so you might have one altimeter on the minus 75 ft limit and the other on the plus 50 ft limit, hence a difference of 125 ft!
Hope this helps!
Most flight manuals on PA38/PA28 type aircraft list the max pressure error correction as plus or minus 50 ft.
That said there are other factors. The Altimeter check should always be done on QNH whilst parked on the apron. Apron elevations are listed in the UK AIP for major UK aerodromes. Without listing all the arguments if you are using QFE there may be other "errors" as you may or may not be using a threshold QFE or aerodrome QFE and not at the "reference" point.
Also when the pressure is measured it is always corrected down to the nearest millibar. E.g measured pressure 1000.9 mb, pilot is passed 1000 mb - in extremis this means a .9 mb error which equals 25 ft (1 mb = 27.3 ft). Hence the quoted of limits of -75/+50 ft (the extra 25 ft on the negative side to cater for the possible .9 mb difference).
If you have more than one altimeter then EACH altimeter should be within the tolerance so you might have one altimeter on the minus 75 ft limit and the other on the plus 50 ft limit, hence a difference of 125 ft!
Hope this helps!
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So you fly happily round under the London TMA at 2450 feet (because you can) and get busted by the CAA for being inside the TMA (which starts at 2500 feet). Your excuse: the altimeter was under-reading by 100 feet?
50 feet, I learned when I did my PPL, is the maximum permissible error. If it's outside that, I'd argue the aircraft isn't airworthy. I certainly wouldn't fly it anywhere near controlled airspace on my way to have it seen to.
50 feet, I learned when I did my PPL, is the maximum permissible error. If it's outside that, I'd argue the aircraft isn't airworthy. I certainly wouldn't fly it anywhere near controlled airspace on my way to have it seen to.
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Anybody got a reference for 50ft? Heard it before, used it myself, never seen it in writing.
I have a reference for 'in the order of' 75ft. AIM 7.2.3.a.3
I have a reference for 'in the order of' 75ft. AIM 7.2.3.a.3
Note the variation between the known field elevation and the altimeter indication. If this variation is in the order of plus or minus 75 feet, the accuracy of the altimeter is questionable and the problem should be referred to an appropriately rated repair station for evaluation and possible correction.
Then, if both altimeters are misreading by 100ft, perhaps the field elevation is wrong?
So you fly happily round under the London TMA at 2450 feet (because you can) and get busted by the CAA for being inside the TMA (which starts at 2500 feet). Your excuse: the altimeter was under-reading by 100 feet?
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Check where on the airfield the elevation is specified. A 50 foot variation between one end of an 800m runway and the other is equates to a gradient of less than 1:50 - difficult to see by eye. If you are checking the altimeter "on chocks", and there is such a slope, it could account for the error.
OC619
OC619
Have you tried tapping the guage!!!!!!!!!!!!
Large aircraft have built in altimeter vibrators. Small aircraft rely on engine vibration to help remove internal friction. FAR 43 Appendix E allows a swing of up to 75 feet at 0-1000 ft due to internal friction..
So you need to ensure that the guage has been "vibrated" before checking the error.
Large aircraft have built in altimeter vibrators. Small aircraft rely on engine vibration to help remove internal friction. FAR 43 Appendix E allows a swing of up to 75 feet at 0-1000 ft due to internal friction..
So you need to ensure that the guage has been "vibrated" before checking the error.
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slim slag, where do I find the document from which you quoted:
"I have a reference for 'in the order of' 75ft. AIM 7.2.3.a.3"
Do you have a web link at all please?
erricferret, the alt was check at threshold elevation with engine running so would have plenty of vibration after power checks etc.
"I have a reference for 'in the order of' 75ft. AIM 7.2.3.a.3"
Do you have a web link at all please?
erricferret, the alt was check at threshold elevation with engine running so would have plenty of vibration after power checks etc.
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http://www.faa.gov/airports_airtraff...7/aim0702.html
or
http://tinyurl.com/25xl4g
7.2.3.a.3
which is just over half way down
or
http://tinyurl.com/25xl4g
7.2.3.a.3
which is just over half way down
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I think the original poster is talking about a G-reg.
The bi-annual pitot check referred to above is done on N-reg only. This can cost up to £500 depending on how far one is away from the nearest firm that has the special equipment for doing it. A lot of people use a firm in Cranfield which charges best part of £200 for driving down. Mind you, flying to Cranfield isn't that much cheaper nowadays
On a G-reg this check isn't done - presumably because the UK doesn't have any significantly elevated airfields so nobody really cares about altimeter errors.
The bi-annual pitot check referred to above is done on N-reg only. This can cost up to £500 depending on how far one is away from the nearest firm that has the special equipment for doing it. A lot of people use a firm in Cranfield which charges best part of £200 for driving down. Mind you, flying to Cranfield isn't that much cheaper nowadays
On a G-reg this check isn't done - presumably because the UK doesn't have any significantly elevated airfields so nobody really cares about altimeter errors.
Check where on the airfield the elevation is specified. A 50 foot variation between one end of an 800m runway and the other is equates to a gradient of less than 1:50 - difficult to see by eye. If you are checking the altimeter "on chocks", and there is such a slope, it could account for the error.
(Note - in some states, Greece for example I think, the aerodrome elevation is the height amsl of the aerodrome reference point - typically the centre of the main runway.
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Yes chaps the aircraft in question is G registered so FAA rules would not really apply.
Not found anything in my POM as this was my first port of call.
Everyone that I have spoken to seems to suggest 50ft is acceptable error, but still do not have conclusive documentation to support our theory to add weight to my dispute with my group member.
Not found anything in my POM as this was my first port of call.
Everyone that I have spoken to seems to suggest 50ft is acceptable error, but still do not have conclusive documentation to support our theory to add weight to my dispute with my group member.
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) Of course if you are flying on an FAA certificate, you fail to follow the advice and have an accident, the FAA could come after you for being 'careless and reckless'. But for your purposes the advice about altimeters should be considered applicable. IMO. Altimeters work the same way all over the world, and the one you are using was probably made and certified in the USA anyway.
But as I asked earlier, if anybody has a reference to 50ft then that would be interesting too. Nobody has as yet delivered. Until they do, and it's in a CAA document, then I suggest that the AIM reference I provided you is the best ammunition you have got.