Light aircraft static driven permissible altimeter tolerance
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Light aircraft static driven permissible altimeter tolerance
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 before the aircraft went into a recent annual and C of A, it has came out the same, still under reading by 100ft. (surely thisa 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
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 before the aircraft went into a recent annual and C of A, it has came out the same, still under reading by 100ft. (surely thisa 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
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
Pitot Static tests/altimeter/ASI calibration checks are called up on each Annual Inspection. I take it that you have compared altimeter readings against another aircraft with the same field barometric setting?
A maintenance organisation doesn't calibrate altimeters, btw - they would be sent away to an instrument repair facility if defective.
A maintenance organisation doesn't calibrate altimeters, btw - they would be sent away to an instrument repair facility if defective.
Last edited by stevef; 13th Jul 2007 at 19:28.
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Plus or minus 50 ft rings a bell ( 100Ft in total)........... can give you the info where to source it but cannot remember the book of words it is in.. have a copy at work if i remember and that is a big If I will look monday and tell you were to find it............PMi'ing me may help remind me 
Emailed the SRG........ Lol thats a larffff
They issued the first copy of the New Licencing Guide for Engineers and one of their fopars in that when describing an example of aircraft one could take to get a group.......... namely "twin piston engined pressurised Cessna metal aircraft" the two examples listed were the Cessna 500 ( Citation Jet) and the Cessna 441 ( "TurboProp" ) Spot the delibrate lack of pistons in any of them, so what chance have you of getting a correct answer
I actually phoned them up and pointed it out which was corrected in the next issue..............
Emailed the SRG........ Lol thats a larffff
They issued the first copy of the New Licencing Guide for Engineers and one of their fopars in that when describing an example of aircraft one could take to get a group.......... namely "twin piston engined pressurised Cessna metal aircraft" the two examples listed were the Cessna 500 ( Citation Jet) and the Cessna 441 ( "TurboProp" ) Spot the delibrate lack of pistons in any of them, so what chance have you of getting a correct answer
I actually phoned them up and pointed it out which was corrected in the next issue..............
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Hi nutloose,
In my experience, the acceptable difference between two altimeters is not the same depending the altitude.
On ground, the maximum permitted is 1Hpa (20 feet) but that difference can be higher in altitude. At FL 300, 100 feet of under reading is nothing, but during short approach in CATII, you can be in a deep trouble.
In all companies I have worked for, 100 feet difference ON GROUND is a NO GO situation.
In my experience, the acceptable difference between two altimeters is not the same depending the altitude.
On ground, the maximum permitted is 1Hpa (20 feet) but that difference can be higher in altitude. At FL 300, 100 feet of under reading is nothing, but during short approach in CATII, you can be in a deep trouble.
In all companies I have worked for, 100 feet difference ON GROUND is a NO GO situation.
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Thanks for all your comments so far guys, hopefully someone can supply me a reference to a definitive answer.
It is funny how everyone I have spoken to, bar the guy I'm having a dispute with say that 100ft is way too much and should be sorted.
He is an old guy with no common sense. He taxiied on some rough pitted grass off of a disused runway for parking at our airfield after I had warned him that the grass was not fit for taxi 2 weeks previous. He continued to be pig headed and said that he "will not be told what is what by those with lower hours than him!" . . . . Consequently he carried on taxiing on this grass to park rather than pull up in front of parking space and push back and dropped nose wheel in a hole and which ended in prop hitting mud and stones and engine had to be stopped.
It was witnessed by instructors and by myself and another group member. He washed off mud with a hose and put aircraft back. When confronted he said that the prop did not need to be checked and the engine was not shock loaded as the engine didn't stop on it's own accord, he stopped it himself!!
He did not see it necessary to get check out by engineers even though massive chunks out of end of prop due to hitting a burried rock in the mud, in his words he has flown her with a more "damaged prop" and it was fine and elected to fly a couple of circuits to prove it was ok.
We locked horns on this point as I am in no position to take his word, not an engineer to say that she is fit to fly putting the safety of myself, passengers, public and our aircraft in his unqualified hands!!
The prop / engine apparently was then sent in to be tested by him and prop was merely dressed, now 3 months later in the C of A / annual thuis prop was replaced after only 900 hours or so. This makes me think that he put her into engineers to just tidy up prop and not tell them the whole story and get shock test etc done - The bloke is a liability!!!
He doesn't want to run the group, but will not hand over the reigns, feel that he has something to hide, financial or other wise, not really sure what I can do. Wonder if CAA would have anything to say about all of this, but I would expect that they wouldn't do a lot.
Sorry to ramble on guys, just illustrating what sort of person I am dealing with here!!
It is funny how everyone I have spoken to, bar the guy I'm having a dispute with say that 100ft is way too much and should be sorted.
He is an old guy with no common sense. He taxiied on some rough pitted grass off of a disused runway for parking at our airfield after I had warned him that the grass was not fit for taxi 2 weeks previous. He continued to be pig headed and said that he "will not be told what is what by those with lower hours than him!" . . . . Consequently he carried on taxiing on this grass to park rather than pull up in front of parking space and push back and dropped nose wheel in a hole and which ended in prop hitting mud and stones and engine had to be stopped.
It was witnessed by instructors and by myself and another group member. He washed off mud with a hose and put aircraft back. When confronted he said that the prop did not need to be checked and the engine was not shock loaded as the engine didn't stop on it's own accord, he stopped it himself!!
He did not see it necessary to get check out by engineers even though massive chunks out of end of prop due to hitting a burried rock in the mud, in his words he has flown her with a more "damaged prop" and it was fine and elected to fly a couple of circuits to prove it was ok.
We locked horns on this point as I am in no position to take his word, not an engineer to say that she is fit to fly putting the safety of myself, passengers, public and our aircraft in his unqualified hands!!
The prop / engine apparently was then sent in to be tested by him and prop was merely dressed, now 3 months later in the C of A / annual thuis prop was replaced after only 900 hours or so. This makes me think that he put her into engineers to just tidy up prop and not tell them the whole story and get shock test etc done - The bloke is a liability!!!
He doesn't want to run the group, but will not hand over the reigns, feel that he has something to hide, financial or other wise, not really sure what I can do. Wonder if CAA would have anything to say about all of this, but I would expect that they wouldn't do a lot.
Sorry to ramble on guys, just illustrating what sort of person I am dealing with here!!
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Altimeter Discrepency
The acceptable descrepency will vary with the altitude. What I mean is the instrument will be more accurate at lower altitudes. Kinda important nearer the floor. Contact the manufacturer using the makers name on the instrument face if you have no access to maint manual or manufacturer manual. There will be a graph of tolerances at varying altitudes. Maybe info on the internet these days who knows and good luck. There are numpties everywhere by da way!
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Yes I'm talking 100ft on the deck! I will try to find out the alt manufacturer and that would be another port of call.
I thought that this would be an easy value to source as a general for light aircraft alt accuracy - Wrong!
I thought that this would be an easy value to source as a general for light aircraft alt accuracy - Wrong!
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That would be in my opinion be a propstrike and as such the engine would need to be pulled for inspection....... Lycoming have indeed altered the definition of prop strikes to include taxying through long grass, water or anything that causes a drop in RPM...indeed knocking the prop with the likes of a hangar door is now also counted as a strike....... the bolt on the back end of the crank would also require replacement as these have been known to fail on a couple of occasions in the US with the loss of life... when it goes you lose drive to the mags, fuel pump if fitted, oil pump and the camshaft...
BUT be careful what you say against a person on a public forum ok as this may come back to haunt you
see
http://www.lycoming.com/support/publ...dfs/SB533A.pdf
http://www.lycoming.com/support/publ...dfs/SB475C.pdf
BUT be careful what you say against a person on a public forum ok as this may come back to haunt you
see
http://www.lycoming.com/support/publ...dfs/SB533A.pdf
http://www.lycoming.com/support/publ...dfs/SB475C.pdf
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Thanks again guys, prop issue was a few months ago and a new prop has been fitted, not sure about shock loading etc tho!
Just need to sort alt issue out at this time, the guy running the group is putting up his share for sale, but has cried wolf before, we'll see if he goes this time!
The reigns have been passed over to another "in his fold" so we'll see if I get more joy out of him, but I feel that he will still have an influence using the new front man as a "puppet" while he is still in the group and not so sure how detached he will be if he leaves.....
Any info on light aircraft max permisible alt error on ground is still what I'm after if anybody has concrete figures on paper, which I can be directed.
Thanks for the word of caution nutloose, trying not to give too much info awaya and too many details and thanks for lycoming docsd too.
Just need to sort alt issue out at this time, the guy running the group is putting up his share for sale, but has cried wolf before, we'll see if he goes this time!
The reigns have been passed over to another "in his fold" so we'll see if I get more joy out of him, but I feel that he will still have an influence using the new front man as a "puppet" while he is still in the group and not so sure how detached he will be if he leaves.....
Any info on light aircraft max permisible alt error on ground is still what I'm after if anybody has concrete figures on paper, which I can be directed.
Thanks for the word of caution nutloose, trying not to give too much info awaya and too many details and thanks for lycoming docsd too.
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Tolerances
http://66.102.9.104/search?q=cache:e4ADfGH4eaoJ:rrp.casa.gov.au/nprm/nprm0109msB_DRAFTac043-09(0)_Nov01.pdf+aircraft+altimeter+tolerances&hl=en&ct=clnk& cd=8
http://www.atsb.gov.au/publications/investigation_reports/2005/AAIR/aair200500074.aspx
I seem to remember a long time ago that the tolerance on a DC10 Alt in STBY mode was checked on the daily and had to be plus/minus 30 Feet with QFE selected.
The first document above says at zero altitude tolerance is plus/minus 20 Feet. I'm not sure which aviation authority it comes from.
http://www.atsb.gov.au/publications/investigation_reports/2005/AAIR/aair200500074.aspx
I seem to remember a long time ago that the tolerance on a DC10 Alt in STBY mode was checked on the daily and had to be plus/minus 30 Feet with QFE selected.
The first document above says at zero altitude tolerance is plus/minus 20 Feet. I'm not sure which aviation authority it comes from.
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Altimeter tolerances
FAR 43 Append. E will list the altimeter checks/tolerances that should answer your question.
Go to www.faa.gov and look up Current regulations and policies. Historical FARs, current FARs, Part 43 then find at the end of the list, Appendix E
Go to www.faa.gov and look up Current regulations and policies. Historical FARs, current FARs, Part 43 then find at the end of the list, Appendix E
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If your aircraft is of US manufacture then the FARs should be your guide. Refer to the manufacturers maintenace requirements, and not LAMS, and this will probably point you to the FARs. If it is a Britsih aircraft and there is nothing in the manufacturers schedule refer to CAA CAAIP's, but not sure which one.
ACX
ACX
Test tolerances here in NZ are +- 20ft at 0 feet, +- 75ft at 40% of max altitude. That said I'm sure one of the local pilots had a look the other day and said the operational limits were something like +40 to -30 feet (or vice-versa). I recall the discussion as we all had a stab at what we thought was correct and he went away to check on it and came back with this slightly odd limit.
Interestingly the reason for the discussion was that one of the light a/c here was reading 100ft out (don't recall which way) on the ground given the local QNH. There were a few theories abounding (the pressure measurements are made a few miles from this airfield) but it turned out to be consistently awry so looked as if the instrument was out & we had it adjusted.
I think many of our rules are based on the UK ones so I'd think your requirements would be similar - would be interested if you find out.
Interestingly the reason for the discussion was that one of the light a/c here was reading 100ft out (don't recall which way) on the ground given the local QNH. There were a few theories abounding (the pressure measurements are made a few miles from this airfield) but it turned out to be consistently awry so looked as if the instrument was out & we had it adjusted.
I think many of our rules are based on the UK ones so I'd think your requirements would be similar - would be interested if you find out.
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Altimeter tolerances for larger aircraft are normally laid down in the maintenance manual, and have tightened up considerably with the introduction of RVSM. For smaller GA aircraft the tolerances are significantly larger, the LAMS gives no guidance on the actual limits and most companies make up there own procedures, normally based on the previously referenced FAR.
Just for info there IS a field adjustment that can be carried out on most GA altimeters by a suitably licensed engineer, and that is to adjust the BARO scale calibration, this is normally the problem with altimeters on the ground and once adjusted properly will normaly fall into limits at altitude.
Hope this helps
Just for info there IS a field adjustment that can be carried out on most GA altimeters by a suitably licensed engineer, and that is to adjust the BARO scale calibration, this is normally the problem with altimeters on the ground and once adjusted properly will normaly fall into limits at altitude.
Hope this helps
