A seasoned pilot told me the other day that if the vacuum system fails while on final approach leaving the Attitude Indicator (AI) inop, the pilot must use localizer minimums even with both glideslope and localizer needles functioning normally.

Is this accurate, or did I misunderstand?

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    $\begingroup$ If possible, check with that guy for the source of info. $\endgroup$ Jul 20, 2016 at 18:25
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    $\begingroup$ As far as I understand it, a vacuum failure in IMC is an emergency. I think the bigger issue is if you have to go missed approach, you can only use the LOC/glideslope until you hit decision altitude then you need to rely on other instruments to get you to your alternate. $\endgroup$
    – Ron Beyer
    Jul 20, 2016 at 21:48

2 Answers 2


For the record, the asker changed the question after I answered, specifying that not declaring an emergency is a condition of the question, so I will address this at the top without modifying the original part:

An attitude indicator is legally required for IFR flight. If equipment becomes inoperative during IFR, the pilot should inform ATC. I do not know that there is any specific legal text that addresses this particular situation you're describing with an ILS approach coupled with an AI failure, but it would be generally accepted by pilots that losing an attitude indicator is an emergency as opposed to losing other required IFR equipment such as the clock. So, I'm going to go with no, not without declaring an emergency.


In that situation depending on the circumstances, declaring a missed approach, an emergency informing ATC of the system failure, and requesting vectors to VMC conditions would be the best option.

In an emergency, you can deviate from rules to meet the needs of the emergency at your discretion, so I don't believe that technically you can't still shoot to minimums for the ILS, but it would be dangerous, especially if the pilot isn't highly proficient, and should be a last resort with no primary gyros.

If an approach needed to be shot, and there was no VMC within range, a 'Precision Approach Radar' approach would likely be the best option if one existed within range. This is can be a 'no-gyro' approach upon request.

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    $\begingroup$ I think the real question is "Can you legally (under normal circumstances) fly an ILS approach with the attitude indicator INOP?", which I am sure there is some technical and unambiguous answer to $\endgroup$ Jul 20, 2016 at 18:46
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    $\begingroup$ @J.Hougaard I would think not because of 91.13 regardless of any other rule, but that depends on who you ask. However, that answer is still neither technical nor unambiguous though. $\endgroup$ Jul 20, 2016 at 18:48
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    $\begingroup$ PARs are not necessarily no-gyro -- my understanding is if you want a no-gyro PAR approach, you have to ask ATC specifically for it. (You can also get a no-gyro ASR/SRA approach, although ASR/SRA is much less precise than a PAR.) $\endgroup$ Jul 20, 2016 at 22:48
  • $\begingroup$ @UnrecognizedFallingObject Thank you for clearing that up! $\endgroup$ Jul 21, 2016 at 9:34
  • $\begingroup$ @UnrecognizedFallingObject obviously, it also depends on the RADAR equipment available $\endgroup$
    – rbp
    Jul 21, 2016 at 18:16

I'm assuming that we're discussing a flight which departed in an airworthy airplane flying under 14 CFR 91 and a vacuum system failure in IMC has rendered the attitude indicator inoperative.

May the pilot fly an ILS approach to minimums? Yes. There is no regulation requiring that the LOC minimums be used.

May the pilot fly the approach without declaring an emergency? Yes. There is no regulation stating that an emergency must be declared. 14 CFR 91.183 (d), however, requires the pilot to report the failure to ATC as it relates to the safety of flight.

  • $\begingroup$ I agree, no emergency need be declared. 14 CFR 91.3(b) makes no requirement for declaring. My school's chief instructor drilled into me that 91.3(b) activates as soon as the PIC thinks "emergency" (or "oh, crap"). 7700/Mayday/declaring are niceties to let ATC know what's going on. Of course, legal and safe aren't always the same thing... $\endgroup$
    – bartonjs
    Jul 27, 2016 at 2:50

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