Steep Spirals: AFH Chapter 9

Handbook Reference

AFH Ch 9

9.steep-spirals. Steep Spirals

A steep spiral is a power-off performance maneuver in which the airplane descends in a constant-radius gliding turn around a point on the ground. It is essentially a series of gliding turns about a point, requiring the pilot to compensate continuously for wind drift in order to maintain a uniform circular ground track. The maneuver develops coordination, planning, division of attention, and orientation while simulating a power-off emergency descent over a forced-landing field.

Purpose and Standards

The steep spiral is a commercial pilot maneuver found in Chapter 9 of the Airplane Flying Handbook and is evaluated under the Commercial Pilot Airman Certification Standards. Standards typically require:

A minimum of three turns (1,080° total) completed in the spiral.
Bank angle not to exceed 60° at the steepest point, with the steepest bank generally on the downwind side of the circle.
Airspeed within ±10 knots of the recommended best-glide speed (or as specified by the manufacturer).
Roll out within ±10° of the entry/clearing heading, on a designated reference.
A constant-radius ground track around the selected reference point.

Entry Procedure

Clear the area with at least two 90° clearing turns. The maneuver should be entered at sufficient altitude to allow at least three 360° turns and recover no lower than 1,500 ft AGL.
Select a prominent ground reference point (road intersection, isolated tree, small structure) in an area suitable for an emergency landing.
Reduce power to idle and pitch for best glide speed (V_BG). Trim the airplane.
Apply carburetor heat as required, and clear the engine periodically (every 360°–500° of turn) by briefly advancing the throttle to prevent shock cooling and spark plug fouling.
Enter the spiral on the downwind side of the reference, where the airplane will be tracking crosswind, so that the steepest bank occurs immediately at entry while groundspeed is highest.

Wind Correction and Bank Control

Because the airplane gliding at a constant indicated airspeed has the highest groundspeed when on the downwind side of the circle, that portion of the turn requires the steepest bank to hold a constant radius. As the airplane progresses around the circle, bank is reduced progressively until reaching the shallowest bank on the upwind side where groundspeed is lowest. Bank is then increased again as the airplane returns to downwind. Conceptually:

Downwind position: highest groundspeed → steepest bank (up to 60°).
Crosswind positions: intermediate groundspeed → intermediate bank.
Upwind position: lowest groundspeed → shallowest bank.

The correction is continuous, not stepwise. The pilot must constantly compare the airplane's track with the reference point and anticipate the next adjustment.

Airspeed and Pitch Control

Airspeed is controlled with pitch attitude, not power, since the engine is at idle. As bank increases, the load factor and stall speed increase, and a slight back pressure may be required to maintain best glide speed; however, over-pitching will cause airspeed decay and a high sink rate. The relationship is:

Load factor in a coordinated turn = 1 / cos(bank angle).
At 60° bank, load factor = 2.0 G, and stall speed increases by approximately 41% (multiplier of √2).

Keep the slip/skid ball centered. Adverse yaw and the need for top rudder in steep gliding turns must be managed with coordinated rudder pressure.

Division of Attention

Throughout the maneuver the pilot must:

Maintain visual reference to the ground point and the horizon.
Cross-check airspeed, altitude, and bank.
Scan for traffic — the spiral covers a large vertical column.
Clear the engine at regular intervals.
Plan the rollout heading well in advance.

Recovery

Recovery is initiated on a predetermined heading or cardinal reference (often the entry heading) and at a safe altitude — no lower than 1,500 ft AGL. Roll out smoothly, simultaneously adding power and pitching to level flight or climb attitude as appropriate, retract carb heat, and reestablish cruise.

Common Errors

Failure to maintain a constant-radius circle (drifting away on downwind, tightening on upwind).
Allowing airspeed to vary excessively as bank changes.
Uncoordinated flight (slipping or skidding in steep banks).
Failure to clear the engine.
Exceeding 60° bank.
Poor planning of rollout heading.
Inadequate clearing turns or fixation on the reference point at the expense of traffic scan.

The steep spiral hones the precise pitch, bank, and rudder coordination a commercial pilot needs to execute a successful emergency power-off approach to a chosen field.

Oral Exam Questions a DPE Might Ask

Q1What is the maximum bank angle in a steep spiral and where in the circle does it occur?

Bank should not exceed 60°, and the steepest bank occurs on the downwind side of the circle where groundspeed is highest, in order to maintain a constant-radius ground track.

Q2How is airspeed controlled during a steep spiral, and what airspeed do you target?

Airspeed is controlled with pitch since the engine is at idle, and the target is the manufacturer's recommended best glide speed (V_BG), held within ±10 knots throughout the maneuver.

Q3Why must you clear the engine during a steep spiral, and how often?

With the throttle at idle for an extended descent, the engine can cool excessively and the plugs can foul. Briefly advancing the throttle every 360° or so prevents shock cooling and ensures power is available for recovery.