If I'm halfway through a barrel roll on final descent, on an ILS, will I get reverse sensing on my glide slope indicator?

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    $\begingroup$ I'm not sure if this is a joke or not... If you are doing barrel rolls in IFR on the glide-slope, you have many other problems to worry about rather than trying to intercept. Are you asking if the glide slope indicator is independent of aircraft attitude? Then the answer would be yes. $\endgroup$ – Ron Beyer May 5 '17 at 2:10
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    $\begingroup$ The first word in the sentence indicates that we're talking about a hypothetical situation. I'm sure that most reasonable people understand this. $\endgroup$ – Koyovis Jul 9 '17 at 4:15

Well first off said stunt is illegal under 91.303 aerobatic flight regs and 91.13 careless and reckless operation of an aircraft. And it's also very dangerous. But no, it would not result in reverse sensing due to the fact that the ILS system is only capable of sensing whether it is receiving more of the 90 Hz signal as opposed to the 150 Hz signal and interprets this as either above or below glideslope. It cannot differentiate between erect and inverted flight.

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  • $\begingroup$ Why would it necessarily be illegal? Couldn't such a maneuver be performed legally with an appropriate aerobatic waiver? $\endgroup$ – J Walters May 5 '17 at 18:48
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    $\begingroup$ You'd have to obtain a waiver from the FAA for this kind of flying near an airport? Could you? Possibly. But I doubt like he'll they're going to authorize this for an experiment like that described above. And then of course you'll have to find an aerobatic airplane which is IFR certified to try this with. $\endgroup$ – Carlo Felicione May 5 '17 at 20:10
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    $\begingroup$ The ILS can't differentiate between erect and inverted flight, but indicates being above the glideslope in world coordinates with the needle down in the aircraft coordinates. But when you are inverted, down in the aircraft coordinates is up in the world coordinates, so you have to fly away from the needle instead of towards. That's what I'd call reverse sensing. $\endgroup$ – Jan Hudec May 7 '17 at 19:56
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    $\begingroup$ By that logic the glideslope sensor would have to sense whether the aircraft is erect or inverted in order for such a reverse sensing to occur. It doesn't. It just senses a more intense signal of one frequency vs another and uses this to position a deviation indicator relative to center. As such even if the aircraft is inverted, maneuvering towards the deviation on glideslope will center the needle. Reverse sensing does not occur. $\endgroup$ – Carlo Felicione May 8 '17 at 0:00
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    $\begingroup$ Any instrument rated pilot who has logged simulator time who says they've never flown an inverted ILS is either lying or unimaginative. $\endgroup$ – Steve V. May 8 '17 at 1:56

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