Straight-In Autorotation in a Single-Engine Helicopter

Objective

Upon completion of this lesson, the student will demonstrate the ability to perform a straight-in autorotation to a power recovery in accordance with FAA-S-ACS-15 Area of Operation VI, Task B. The student will identify energy management principles, explain the effects of environmental factors on autorotation performance, manage rotor RPM within normal limits, select appropriate landing areas, and execute proper deceleration techniques while maintaining situational awareness throughout the maneuver.

Content

Regulatory Requirements

Per 14 CFR 61.87(n), student pilots must receive training in autorotational flight before solo flight. Commercial pilot applicants must demonstrate autorotation proficiency per 14 CFR 61.127(b)(3). The practical test standards are defined in FAA-S-ACS-15, which requires maintaining autorotation airspeed ±10 knots and terminating to a stabilized hover within 200 feet of a designated point.

Autorotation Aerodynamics and Energy Management

PH.VI.B.K3 Energy Management: Think of autorotation like a bicycle coasting downhill - the helicopter trades altitude for rotor energy. The main rotor becomes a windmill, with upward airflow through the rotor disc maintaining rotor RPM. Energy management involves three key elements: kinetic energy (airspeed), potential energy (altitude), and rotor energy (stored in rotor disc inertia).

PH.VI.B.K2 Main rotor (Nr) speed: Normal rotor RPM must be maintained throughout autorotation. In most training helicopters, this is 97-107% RPM. The collective controls rotor RPM - lowering collective decreases disc loading and allows RPM to recover. Rotor inertia stores energy that will be used during the flare and touchdown phases.

Environmental Factors Affecting Autorotation Performance

PH.VI.B.K1 Effects of wind, weight, temperature, and density altitude:

• Wind: Headwind increases glide distance and reduces groundspeed at touchdown. Tailwind decreases glide distance and increases groundspeed. Crosswind requires crab angle during descent with heading alignment during flare.
• Weight: Heavier helicopters have higher descent rates and faster autorotation airspeeds. Rate of descent increases with the square of the weight increase.
• Temperature/Density Altitude: High density altitude reduces air density, requiring higher indicated airspeed to maintain the same energy state. True airspeed will be higher than indicated.

PH.VI.B.K5 Effect of varying bank angles, airspeeds, and rotor rpm:

• Bank angles increase load factor and descent rate - maintain wings level except for wind correction
• Airspeed below best glide increases descent rate and reduces glide distance
• Low rotor RPM reduces stored energy available for flare; high RPM may lead to overspeed during recovery

Causes and Effects of High Descent Rates

PH.VI.B.K4: High descent rates result from:

• Excessive forward airspeed (diving attitude)
• Low rotor RPM (insufficient energy management)
• High gross weight or density altitude
• Improper collective position

Effects include reduced reaction time, increased stress on airframe, difficulty in flare timing, and potential for hard landing or dynamic rollover.

Risk Management Considerations

PH.VI.B.R1 Low entry altitudes: Minimum 500 feet AGL for training autorotations. Insufficient altitude eliminates recovery options and reduces margin for error.

PH.VI.B.R2 Flight control inputs: Abrupt or excessive inputs can cause rotor RPM deviations, uncommanded attitude changes, or loss of control. Use smooth, deliberate control movements.

PH.VI.B.R3 Turbulence, including wake turbulence: Avoid practice in turbulent conditions. Wake turbulence from other aircraft can cause loss of control during autorotation.

PH.VI.B.R4 Windshear: Monitor for windshear indications. Sudden changes in wind can dramatically affect glide path and energy management.

PH.VI.B.R5 Energy management: Maintain proper airspeed and rotor RPM throughout. Monitor energy state continuously - altitude, airspeed, and rotor RPM are your three bank accounts.

PH.VI.B.R6 & PH.VI.B.R7 & PH.VI.B.R8 Main rotor speed management: Operating outside normal RPM range degrades performance and may cause mechanical damage. Low RPM reduces flare capability; high RPM may cause overspeed during power recovery.

PH.VI.B.R9 Excessive rate of descent: Monitor vertical speed indicator. Excessive descent rates reduce flare effectiveness and increase touchdown forces.

PH.VI.B.R10 Powerplant failure during practice: If actual engine failure occurs during practice autorotation, continue the autorotation to landing - do not attempt power recovery.

PH.VI.B.R11 Collision hazards: Clear area before entry. Maintain visual scanning for other aircraft throughout maneuver.

PH.VI.B.R12 & PH.VI.B.R13 Terminating autorotations and power recovery: Timing is critical. Too early wastes stored rotor energy; too late may result in tail strike or hard landing. Power recovery must be smooth and coordinated.

PH.VI.B.R14 Distractions and situational awareness: Maintain outside visual reference. Avoid fixation on instruments. Prioritize aircraft control, energy management, then navigation.

Autorotation Technique

1. Entry: Lower collective smoothly to maintain rotor RPM, adjust cyclic for best glide airspeed
2. Glide: Maintain constant airspeed and rotor RPM, compensate for wind drift
3. Flare: Aft cyclic to trade airspeed for reduced descent rate
4. Power Recovery: Smoothly raise collective while adding power, coordinate with anti-torque pedals

Schedule

Equipment

Required References

• FAA-H-8083-21B Rotorcraft Flying Handbook, Chapter 11
• FAA-S-ACS-15 Private Pilot Helicopter Practical Test Standards
• Pilot’s Operating Handbook for aircraft being used
• Sectional chart for local area
• FAA-H-8083-25B Pilot’s Handbook of Aeronautical Knowledge, Chapter 11

Materials and Visual Aids

• Whiteboard or tablet for energy management diagrams
• Helicopter rotor disc model for flow demonstration
• Autorotation profile chart specific to aircraft type
• Wind calculation worksheet
• Checklist placards

Instructor Actions

1. Brief autorotation aerodynamics using bicycle coasting analogy - “Just like coasting downhill builds speed, we’re trading altitude for rotor energy”
2. Demonstrate energy management concept using three-account analogy: altitude account, airspeed account, rotor RPM account
3. Show effects of environmental factors using POH performance charts and current conditions
4. Review emergency checklist procedures per aircraft POH
5. Demonstrate clearing turn and radio call: “Practice area traffic, Helicopter 12345, entering autorotation practice at 1,500 feet, 2 miles southwest of airport”
6. Select suitable practice area - minimum 500 feet AGL over unpopulated area with multiple forced landing options
7. Demonstrate proper entry technique: “Watch my collective movement - smooth and deliberate, not a rapid chop”
8. Narrate energy management throughout: “Notice how I’m trading airspeed for reduced descent rate during the flare”
9. Show proper power recovery timing: “Power application begins as the flare arrests our descent rate”
10. Demonstrate wind compensation techniques using coordinated flight principles
11. Guide student through first autorotation with continuous coaching
12. Monitor student rotor RPM management and provide immediate feedback
13. Correct any tendency toward excessive bank angles or improper airspeeds
14. Emphasize visual references for attitude control rather than instrument fixation

Student Actions

1. Complete autorotation checklist items as briefed
2. Make appropriate radio calls before entering practice area
3. Perform clearing turn and select suitable landing area with instructor guidance
4. Demonstrate proper entry technique with smooth collective lowering
5. Establish and maintain best glide airspeed ±10 knots throughout descent
6. Maintain rotor RPM within normal operating range (typically 97-107%)
7. Compensate for wind drift using appropriate crab angle
8. Execute proper flare technique to reduce descent rate
9. Apply power smoothly during recovery phase
10. Coordinate anti-torque pedal inputs with power application
11. Terminate maneuver in stabilized hover within 200 feet of designated point
12. Demonstrate situational awareness by scanning for traffic and obstacles
13. Verbalize energy management decisions throughout maneuver

Completion Standards

The student meets the completion standards when they can demonstrate all required skills per FAA-S-ACS-15 Area of Operation VI, Task B:

• PH.VI.B.S1: Complete appropriate autorotation checklist without prompting
• PH.VI.B.S2: Make clear, accurate radio calls for practice area entry and departure
• PH.VI.B.S3: Select landing areas that are suitable for actual autorotation (size, surface, obstacles)
• PH.VI.B.S4: Perform adequate clearing turn before maneuver entry
• PH.VI.B.S5: Enter autorotation at minimum 500 feet AGL in practice area
• PH.VI.B.S6: Initiate maneuver at proper point relative to selected landing area
• PH.VI.B.S7: Establish autorotation airspeed within ±10 knots and maintain throughout descent
• PH.VI.B.S8: Maintain rotor RPM within manufacturer’s specified normal operating range
• PH.VI.B.S9: Demonstrate wind compensation to track toward selected landing area
• PH.VI.B.S10: Execute flare that provides adequate tail boom clearance (minimum 3 feet)
• PH.VI.B.S11: Initiate smooth power recovery without rotor RPM deviation
• PH.VI.B.S12: Terminate in stabilized hover within 200 feet of designated point at recovery altitude

Additional completion requirements:

• Explain energy management principles using proper terminology
• Identify effects of current weather conditions on autorotation performance
• Demonstrate understanding of autorotation risk factors through proper technique
• Complete minimum of three consecutive autorotations meeting ACS standards