qxeguy
Posts: 81
Joined: Wed Nov 26, 2003 5:53 am

Legal Altimeter Error For IFR Flight

Fri Apr 29, 2005 7:56 am

Anyone who is IFR rated knows (or SHOULD know) that your allowable altimeter error is +/-75 feet. However, my question is if this is a legal regulation. They only thing I could find in the FAR/AIM was (in the Aim) where it RECOMMENDS that if your altimeter is off more than 75 feet it should be serviced. Is there a LEGAL limit to the allowable error, and if there is what is the FAR reference? Thanks!
I fly boxes. Boxes don't bitch. Boxes don't barf. Boxes don't get drunk and do a number 2 on the beverage cart.
 
CosmicCruiser
Posts: 2055
Joined: Tue Feb 22, 2005 3:01 am

RE: Legal Altimeter Error For IFR Flight

Fri Apr 29, 2005 9:32 pm

FAR 91.411 states (I'll abbreviate a little)" No person may operate an airplane IFR unless---- (1) Within the preceeding 24 mo. each static press. sys., each ALTIMETER sys .... has been tested and inspected and found to comply with Appendix E of Part 43 of this chapter. " It's not a recommendation.
 
qxeguy
Posts: 81
Joined: Wed Nov 26, 2003 5:53 am

RE: Legal Altimeter Error For IFR Flight

Fri Apr 29, 2005 11:04 pm

Thanks for that. I am aware of the inspection requirements. I am looking for the legal allowable error. So, lets say the altimeter wacks out 6 months after inspection and is 77 feet off. Or even worse, 350 feet off. I understand that is unsafe and I would not fly with it, but is it ILLEGAL? If so, where does it say that. I am beginning think it is legal. Dumb, but legal.
I fly boxes. Boxes don't bitch. Boxes don't barf. Boxes don't get drunk and do a number 2 on the beverage cart.
 
ThePinnacleKid
Posts: 497
Joined: Wed Feb 23, 2005 9:47 am

RE: Legal Altimeter Error For IFR Flight

Fri Apr 29, 2005 11:48 pm

First off, the altimeter requirements for IFR and VFR are different ... The required things for VFR operations can be found in 91.205 (b). All the required stuff for IFR ops is under 91.205 (d).

According to 91.205 (d)... "For IFR flight, the following instruments and equipment are required:" 1...2....3...4... 5. Sensitive altimeter adjustable for barometric pressure........

As far as operating and the 75' thing. 91.411 and its Appendix E is where the 75' part of the rule comes in... as Cosmic said... But the requirement that the altimeter stays within its limits is not stated directly but it is found in the "mother reg" of 91.7. There it states "(a) No person may operate a civil aircraft unless it is in an airworthy condition. (b) The pilot in command of a civil aircraft is responsible for determining whether that aircraft is in condition for safe flight. The pilot in command shall discontinue the flight when unairworthy mechanical, electrical or structural conditions occur."

So, to be "airworthy" for IFR ops (a)you have to have the altimeter and it must be sensitive to barometric pressure and (b) as PIC you must ensure it is within its legal limits (75' error) in order to not bust the reg by operating an unairworthy aircraft.

hope that helps, Chris

[Edited 2005-04-29 16:53:41]

[Edited 2005-04-29 16:56:07]
"Sonny, did we land? or were we shot down?"
 
qxeguy
Posts: 81
Joined: Wed Nov 26, 2003 5:53 am

RE: Legal Altimeter Error For IFR Flight

Sat Apr 30, 2005 2:26 am

Quoting ThePinnacleKid (Reply 3):
as PIC you must ensure it is within its legal limits (75' error) in order to not bust the reg by operating an unairworthy aircraft.

So, what you are saying is this "75' legal limit" is not defined specifically in the FAR's. Only the safety of flight issue. That is what I am looking for.
I fly boxes. Boxes don't bitch. Boxes don't barf. Boxes don't get drunk and do a number 2 on the beverage cart.
 
727EMflyer
Posts: 538
Joined: Wed Mar 09, 2005 3:22 am

RE: Legal Altimeter Error For IFR Flight

Sat Apr 30, 2005 4:33 am

AOPA's Flight Training magazine this month has an article that addresses issues like this! The "Legal Briefing" column is talks about interpretation of regulations by the FAA and their use in judgements by the NTSB in an accident or incident investigation. You should be able to see the article if you go to http://www.aopa.org where they archive all the issues.
The thrust of the article is that there is a law on the books stating that the NTSB must accept as law any interpretation made by the FAA of a regulation as law. These interpretations are in the form of guidance published in the AIM, advisory circulars etc. So, if the AIM says it, you better do it! You might get away with flying with a faulty altimeter, but if you get into an accident they'll wipe your nose with it!
 
ThePinnacleKid
Posts: 497
Joined: Wed Feb 23, 2005 9:47 am

RE: Legal Altimeter Error For IFR Flight

Sun May 01, 2005 7:13 am

Quoting Qxeguy (Reply 4):
So, what you are saying is this "75' legal limit" is not defined specifically in the FAR's.

Not quite what I was saying... The FAR's do specifically spell it out.. just in two different places is what I was getting at. Like most things in government, the regs were written by Lawyers, not Pilots.. so everything is FUBAR as it goes.... that being said... the FAR's spell out specifically the 75' rule by saying A.) to be in compliance with inspections and be considered Airworthy it has to be within 75'. So that is what it takes to be airworthy... BUT THEN, B.) they put in a totally different place that the PIC must ensure the aircraft is in Airworthy condition to operate the flight. SOOOOOOOO, in a very long round-a-bout way of doing it they say the altimeter must be within 75' tolerances.....

-Chris
"Sonny, did we land? or were we shot down?"

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