The aerobatic "box"
Where do we judge (we mean, other than on cold, windy and frequently wet airfield!)?
All aerobatic figures are judged in and relative to the aerobatic performance zone - we call it the "box". This is nominally a 1,000m cube of air (effectively less 'tall' for any class below Unlimited....) with its lower face at 100m above the ground and defined by two land-based axes:
- The "A" or main box axis is aligned with the competition wind (flight along this axis will by definition therefore be either into wind or down wind).
- The "B" or cross box axis is aligned at 90° to the main / "A" axis.
- Ideally, box markers on the ground define the centre and edges of the box.
- The height above the ground of the minimum allowable flying altitude (the "bottom" or "base" of the box) varies depending on the class of competition being flown – highest for Club, lowest for Unlimited.
- Judges sit in a line parallel to the "A" axis, but set back between 100m and 250m from the near edge of the box. This gives them the best vantage point to judge the flights.
- The "competition wind" can be from the left or right (always on the "A" axis) and is declared by the Chief Judge or the Contest Director before competition flights start.
- The orientation of the box and the wind direction is important – figures must be flown in the correct direction and on the "A" axis, so it is important that judges understand the location and orientation of the box.
If a figure is intended to be flown on the "A" axis (as indicated by the sequence diagram), any deviations from this orientation are penalised by a downgrade of 1 point per 5° of error seen (or 0.5 points per 2.5° if possible). This applies both to the main "A" axis and the cross "B" box axis. A figure may start on the main axis and finish on the cross box axis or vice-versa – in each stage of the figure, the correct axis orientation must be maintained.
Figures that start on the "A" axis must be flown in the correct direction (into wind or down wind) otherwise the figure is zeroed. This absolute requirement does not apply to figures started on the "B" axis.
Figures that start on or turn onto the cross box axis do not have to have the "B" axis element flown in a particular direction – although the direction chosen must make sense compared to the sequence diagram.
If a sequence is interrupted (ie. a "break" is taken) before the start of a particular cross box figure then at the restart that figure must be flown in the direction established by the pilot before the break was taken.
Figures that are flown too far to the left/right or too near/far away compared to their ideal location and/or the box boundary receive Position penalties. A figure that starts behind the judges should be graded normally but recorded as “Behind” and a majority decision taken after the flight.
At international events excursions beyond the four vertical faces of the box are often recorded by an electronic position-detection system and additional “Box Out” penalties are awarded.