In the US, is it legal to cover up some of the required gyro instruments during flight under IFR in actual IMC?
The purpose being for "partial panel" practice.
In the US, is it legal to cover up some of the required gyro instruments during flight under IFR in actual IMC?
The purpose being for "partial panel" practice.
To my knowledge there's nothing illegal about practicing partial panel in real IMC, however it's a spectacularly bad idea to do so. A failure of vacuum instruments in IMC is an emergency because you can easily lose orientation and dig a big hole in the ground. A safety pilot won't be able to help unless they have a separate set of instruments to rely on, and even then upset recovery in IMC is inherently less safe.
If you want to practice partial panel pleeeeease do so in VMC, with a safety pilot.
14 CFR 91.205(a) states (emphasis added):
(a) General. Except as provided in paragraphs (c)(3) and (e) of this section, no person may operate a powered civil aircraft with a standard category U.S. airworthiness certificate in any operation described in paragraphs (b) through (f) of this section unless that aircraft contains the instruments and equipment specified in those paragraphs (or FAA-approved equivalents) for that type of operation, and those instruments and items of equipment are in operable condition.
So the question is: if an instrument is covered, then is it "in operable condition"?
My interpretation would be no: if an instrument is covered, then you can't see what it says, so it's not in operable condition. That would mean that, if that instrument is required for flight, then flying with it covered is illegal.
That said, someone might disagree and say that the instrument is in operable condition, because you can simply remove the cover in order to see what it says. I would disagree with that, because a covered instrument clearly does not provide the safety benefits that an uncovered instrument does.
I did a search in the FAA's "Letter of Interpretation" database, and there didn't seem to be any letters about whether or not a covered-up instrument is "in operable condition". So it seems like this question hasn't been legally decided yet.
I'm certain that there will be some disagreement with my answer, but the regulation (FAR 91.205 shown in pertinent part below) is pretty clear to me that you can't legally operate in the manner described by your question.
Specifically if you purposely render a required piece of equipment, such as the attitude indicator, "inoperable" (meaning it no longer functions in the manner for which it was certified ), you will not be in compliance with FAR 91.205.
Imagine flying IMC with the aircraft's artificial horizon and directional gyro [required by FAR 91.205 (d) (8) and (9)] covered up and you are being vectored for final approach with ATC using minimum separation standards between other IFR aircraft (B737 for example) and you have difficulty taking a turn as expected or holding altitude as required. Putting other IFR aircraft at risk while required instruments in your aircraft are rendered "inoperable" on purpose, I believe is contrary to the FARs and certainly good judgement.
§91.205 Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements.
(a) General. Except as provided in paragraphs (c)(3) and (e) of this section, no person may operate a powered civil aircraft with a standard category U.S. airworthiness certificate in any operation described in paragraphs (b) through (f) of this section unless that aircraft contains the instruments and equipment specified in those paragraphs (or FAA-approved equivalents) for that type of operation, and those instruments and items of equipment are in operable condition.
(d) Instrument flight rules. For IFR flight, the following instruments and equipment are required:
(1) Instruments and equipment specified in paragraph (b) of this section, and, for night flight, instruments and equipment specified in paragraph (c) of this section.
(2) Two-way radio communication and navigation equipment suitable for the route to be flown.
(3) Gyroscopic rate-of-turn indicator, except on the following aircraft:
(i) Airplanes with a third attitude instrument system usable through flight attitudes of 360 degrees of pitch and roll and installed in accordance with the instrument requirements prescribed in §121.305(j) of this chapter; and
(ii) Rotorcraft with a third attitude instrument system usable through flight attitudes of ±80 degrees of pitch and ±120 degrees of roll and installed in accordance with §29.1303(g) of this chapter.
(4) Slip-skid indicator.
(5) Sensitive altimeter adjustable for barometric pressure.
(6) A clock displaying hours, minutes, and seconds with a sweep-second pointer or digital presentation.
(7) Generator or alternator of adequate capacity.
(8) Gyroscopic pitch and bank indicator (artificial horizon).
(9) Gyroscopic direction indicator (directional gyro or equivalent).