Narrative:

Weather was clear with good visibility. We were cleared for visual approach to runway 24 mvy. Checked in with mvy tower and cleared for left downwind to runway 24. I descended to pattern altitude (1500msl) and entered the left downwind. Tower instructed us to extend our downwind for landing traffic/departure and told us the tower would call our base turn. As we continued on the downwind I observed an aircraft slightly higher than our altitude and between us and the extended centerline of mvy runway 24 just past the shoreline (about 4 to 5 miles from mvy). The aircraft was flying erratically and there was no TCAS target. A white biplane was observed spinning down to our altitude and was near to abeam of our position when tower called our base turn. By that time the biplane was beginning a loop. I refused the turn from tower and continued downwind until I was sure to be clear of the aerobatic traffic. We then turned base to final with no incident. When I advised tower of the incident the reply was (he; the biplane is not in my airspace).tower should not extend traffic into airspace they are not going to be responsible for. Aerobatic activities should be NOTAM'ed. I asked a few questions after my passenger told me several biplanes operated commercially in the area. I was told there are two biplanes operating out of a field near mvy; one of which matched the aircraft I observed. The biplane operators should not operate near active runway approach paths. If commercial aerobatic operations are going on; how about designating a box for aerobatic operations like found anywhere else there are regular aerobatic ops like st. Augustine; fl. If the aircraft had his transponder on we might have had more warning of his proximity and I am sure if his transponder was on we would have got an RA. That might be why his transponder was off. I don't know if it is common practice to kill your squawk while doing aerobatics but I would recommend leaving it on. Tower did not seem to be concerned; mvy FBO personnel were familiar with the aerobatic operations.

Google
 

Original NASA ASRS Text

Title: LR60 Captain on extended left downwind at MVY reports conflict with aircraft doing aerobatics the Tower reported the traffic was not in MVY airspace.

Narrative: Weather was clear with good visibility. We were cleared for visual approach to Runway 24 MVY. Checked in with MVY Tower and cleared for left downwind to Runway 24. I descended to pattern altitude (1500msl) and entered the left downwind. Tower instructed us to extend our downwind for landing traffic/departure and told us the tower would call our base turn. As we continued on the downwind I observed an aircraft slightly higher than our altitude and between us and the extended centerline of MVY Runway 24 just past the shoreline (about 4 to 5 miles from MVY). The aircraft was flying erratically and there was no TCAS target. A white biplane was observed spinning down to our altitude and was near to abeam of our position when tower called our base turn. By that time the biplane was beginning a loop. I refused the turn from tower and continued downwind until I was sure to be clear of the aerobatic traffic. We then turned base to final with no incident. When I advised tower of the incident the reply was (he; the biplane is not in my airspace).Tower should not extend traffic into airspace they are not going to be responsible for. Aerobatic activities should be NOTAM'ed. I asked a few questions after my Passenger told me several biplanes operated commercially in the area. I was told there are two biplanes operating out of a field near MVY; one of which matched the aircraft I observed. The biplane operators should not operate near active runway approach paths. If commercial aerobatic operations are going on; how about designating a box for aerobatic operations like found anywhere else there are regular aerobatic ops like St. Augustine; FL. If the aircraft had his transponder on we might have had more warning of his proximity and I am sure if his transponder was on we would have got an RA. That might be why his transponder was off. I don't know if it is common practice to kill your squawk while doing aerobatics but I would recommend leaving it on. Tower did not seem to be concerned; MVY FBO personnel were familiar with the aerobatic operations.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.