The objective of the steep spiral is to provide a flight maneuver for rapidly dissipating substantial amounts of altitude while remaining over a selected spot. This maneuver is especially effective for emergency descents or landings. A steep spiral is a gliding turn where the pilot maintains a constant radius around a surface-based reference point while rapidly descending—similar to the turns around a point maneuver. Sufficient altitude must be gained prior to practicing the maneuver so that at least three 360° turns are completed. [Figure 9-2] The maneuver should not be allowed to continue below 1,500 feet above ground level (AGL) unless an actual emergency exists.
The steep spiral is initiated by properly clearing the airspace for air traffic and hazards. In general, the throttle is closed to idle, carburetor heat is applied if equipped, and gliding speed is established. Once the proper airspeed is attained, the pitch should be lowered and the airplane rolled to the desired bank angle as the reference point is reached. The steepest bank should not exceed 60°. The gliding spiral should be a turn of constant radius while maintaining the airplane’s position to the reference. This can only be accomplished by proper correction for wind drift by steepening the bank on downwind headings and shallowing the bank on upwind headings, just as in the maneuver, turns around a point. During the steep spiral, the pilot must continually correct for any changes in wind direction and velocity to maintain a constant radius.
Operating the engine at idle speed for any prolonged period during the glide may result in excessive engine cooling, spark plug fouling, or carburetor ice. To assist in avoiding these issues, the throttle should be periodically advanced to normal cruise power and sustained for a few seconds. If equipped, monitoring cylinder head temperatures provides a pilot with additional information on engine cooling. When advancing the throttle, the pitch attitude must be adjusted to maintain a constant airspeed and, preferably, this should be done when headed into the wind.
Maintaining a constant airspeed throughout the maneuver is an important skill for a pilot to develop. This is necessary because the airspeed tends to fluctuate as the bank angle is changed throughout the maneuver. The pilot should anticipate pitch corrections as the bank angle is varied throughout the maneuver. During practice of the maneuver, the pilot should execute three turns and roll out toward a definite object or on a specific heading. During rollout, the smooth and accurate application of the flight controls allow the airplane to recover to a wing’s level glide with no change in airspeed. Recovering to normal cruise flight would proceed after the establishment of a wing’s level glide.
Common errors when performing steep spirals are:
- Not clearing the area
- Inadequate pitch control on entry or rollout
- Gaining altitude
- Not correcting the bank angle to compensate for wind
- Poor flight control coordination
- Ineffective use of trim
- Inadequate airspeed control
- Becoming disoriented
- Performing by reference to the flight instrument rather than visual references
- Not scanning for other traffic during the maneuver
- Not completing the turn on designated heading or reference