Are there any generally accepted rules for this?
I recall that there is a recommendation to have any transponder switched OFF to avoid triggering commercial aircraft TCAS (by the rate of closure) but that makes the aero aircraft invisible to GA too.
Typically aerobatic aircraft fly with the transponder off so as not to trigger TCAS. The requirement for aircraft with an electrical system and transponder fitted, to have the transponder ON while airborne might change things.
It’s not clear to me why the Transponder can’t be used in Mode A as a sensible compromise.
You could also imagine to set a given squawk (eg 6666) indicating aeros, or an “aerobatics” mode for the mode S ones.
It depends what you mean. A simple roll or training. We do acro from 2000 ft AGL to 5-6000 ft typically. To get enough G space in vertical direction, I have to fly for an hour or so to the nearest strip with high enough G airspace. So acro is usually done within controlled airspace, where you get a “box”. You have to tell ATC when you are finished, so they can close the “box” again. Never heard of any problems with transponder, it’s always on (mode C).
In G its custom to tell on the radio where you are and at what altitudes. Then tell when you are finished. Transponder is on. Essentially the same as in controlled space. But it depends.
In the UK you can sqwak 7004 for aeros but most of them don’t have transponders, on competitions usually the box is notamed
Other than that is see and avoid, usually it is much easier to spot or to avoid someone looping than cruising !
7004, tell who ever is vaguely responsible for the airspace what you are doing and where (aerobating over Selsey between 3,000 and 5,000 feet), and landing light on if you will. It all could help and you do reasonably often hear under a basic service the provider report that someone is aerobating over x, between x and y. I once had Farnborough ask me to explain my rapid height variance as I was barrel rolling along a track (not that I was busting any airspace), they just couldnt understand the cause. The explanation broguht a smile.
A fair bit of aerobatics take place under the flightpaths near the major London airports – and modern aerobatic aircraft will trigger TCAS given the rate of climb in a vertical manoeuvre, hence the practice of not using a transponder.
Further away from CAS the use of transponder is normal.
RobertL18C wrote:
hence the practice of not using a transponder.
But again, that would not happen with altitude replies turned off — or would it?
It’s a good point, am not sure why they don’t use Mode A.
Actually mode A will causes much more problems for ATSU separation software as they tend assume “any level” with mode A only, so you probably better switching to it off or confirm your height?
Also, I am less convinced about TCAS warnings while doing aeros in GA aircraft unless you are that really close to CAS (e.g. aeros under London TMA with 500ft margins), you are neither faster than a twin cruising or a turbine climbing from OCAS into CAS?
So not sure you will trigger that much “separation warnings” if you have sufficient margins to controlled airspace, however it may trigger many glitches on radar screens like “airspace busts” (usually a 5 min extrapolation) or “emergency warnings” (quick loss of height)…
