Pivotal altitude

At the pivotal altitude, a turn can be made at any distance from the pylon with appropriate bank, and the pylon will appear to remain stationary

Pivotal altitude is the height for a given ground speed at which the line of sight from the cockpit directly parallel to the lateral axis of the aircraft will remain stationary on an object on the ground.^[1]

A rule of thumb for calculating the pivotal altitude H in feet, given the speed in knots $v$, is

$H = \frac {v^2}{11.3}$

References

1. United States Department of Transportation, Federal Aviation Administration, FAA-H-8083-3A, Airplane Flying Handbook