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Assuming you are aerobatically trained, IFR rated, have an aircraft that is rated for the aerobatic maneuvers you are planning to perform (let us assume that it is acrobatic category, even), and the aircraft in question is type certified and equipped for flight under IFR, how would you plan out and safely execute a set of aerobatic maneuvers in IMC (think solid cloud, but without serious up/downdrafts, icing, or lightning hazards) while flying under IFR? Can you define a "box clearance" in an IFR flight plan, akin to a VFR aerobatic box, only defined by coordinates or intersections instead of ground reference points? How feasible is it to carry out the Aresti catalog maneuvers by reference to flight instruments alone?

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    $\begingroup$ You can indeed ask for a block altitude and your clearance would be "block 14,000 to 16,000." $\endgroup$ – rbp Jan 30 '15 at 0:40
  • $\begingroup$ @rbp -- block altitudes I know about, but for acro in IMC, I'd want positive horizontal separation as well, which is why I asked about the "box clearance" -- the two would be used together to get a protected airspace volume to operate in. $\endgroup$ – UnrecognizedFallingObject Jan 30 '15 at 0:42
  • $\begingroup$ Wave boxes in Class A airspace for gliders are defined via LOAs. Not sure you could get an IFR Acro box. $\endgroup$ – rbp Jan 30 '15 at 0:43
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    $\begingroup$ What's the point of aerobatics if nobody can see you? $\endgroup$ – raptortech97 Jan 30 '15 at 2:44
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    $\begingroup$ You could get a sector clearance. aka, you'd be cleared to operate between the ABC VOR's 090 to 140 radials from 50 to 80 DME, block altitude 4000 to 8000 or whatever you'd want to try. $\endgroup$ – slookabill Jan 30 '15 at 19:13
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No - you don't do it.

First and obvious reason, there's no body to see it.

Perhaps much more important is safety though. When pulling a loop, it's not like flight simulator where you just yank the stick aft and watch the attitude indicator (AI). An aerobatic pilot is constantly checking his attitude by looking at his wing tips, quickly glancing the left and right sides back and forth.

In fact, the AI is usually caged (meaning it is locked to prevent rotation) in such violent maneuver. The proper procedure is cage the AI, perform the maneuver, check straight and level (visually), then uncage the AI. If you don't, the gyroscope will tumble quite some time before it settles again, rendering it useless. Meaning, if you perform in IMC, you won't have accurate AI information for recovery.

For nearly vertical maneuvers (e.g. stall turn, rolling while vertical), even a functioning AI wouldn't help, since horizontal direction is undefined in this state. The AI and compass will just flip, yet you have no way to determine which way you go.

Violent G-forces also mean it is much more difficult to read instruments during such maneuver.

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  • $\begingroup$ Would it be possible to do this if you had an attitude reference instrument that didn't need to be caged? $\endgroup$ – UnrecognizedFallingObject Jan 30 '15 at 3:21
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    $\begingroup$ I guess fighter jets have it. I've never flown one though! $\endgroup$ – kevin Jan 30 '15 at 3:22
  • $\begingroup$ @kevin: I would expect most glass cockpits not to need caging as these use a set of (vibrating or laser) rate gyros and computer integration rather than free spinning gyro. Though apparently not all software is certified for it. $\endgroup$ – Jan Hudec Feb 1 '15 at 0:09
  • $\begingroup$ Aside: Look up gimbal lock on Apollo 11/13. $\endgroup$ – copper.hat Feb 4 '15 at 8:07
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    $\begingroup$ @JanHudec In the linked full report you can read that according to the manufacturer, it will indicate correctly during a roll, but not during a loop. Or as kevin says when rolling when nearly vertical. $\endgroup$ – Vladimir F Mar 27 '16 at 20:49

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