Straight-In Autorotation in a Single-Engine Helicopter

Objective

By the end of this lesson, the student will be able to execute a straight-in autorotation from at least 500 feet AGL to a power-off landing with engine failure recognition within 3 seconds, maintaining rotor RPM within limits, achieving the recommended airspeed ±10 knots, and touching down smoothly within 200 feet of the intended touchdown point, in accordance with FAA-S-ACS-15 PH.VI.B.

Content

Introduction to Autorotation

An autorotation is the helicopter pilot’s primary emergency response to engine failure. Think of it as a controlled crash landing where we trade altitude for rotor energy. The rotor becomes a giant pinwheel, with upward airflow through the disk keeping the blades spinning and providing lift for a survivable landing.

Aerodynamic Principles

During autorotation, the rotor disk divides into three regions:

• Driven region (root to 25% radius): Airflow moves inward and up, creating drag
• Driving region (25% to 70% radius): Airflow provides the energy to keep rotors turning
• Stall region (70% to tip): High angle of attack causes stall and drag

The key is maintaining proper rotor RPM by managing the collective pitch angle. Too much collective bleeds energy; too little causes excessive descent rate.

Entry Procedures

Per FAA-H-8083-21B, autorotation entry must be immediate upon engine failure recognition. Lower the collective fully while applying appropriate anti-torque pedal input to maintain heading. Establish the manufacturer’s recommended autorotation airspeed immediately.

Minimum Entry Altitude Requirements

14 CFR 91.119 establishes minimum safe altitudes, but for training autorotations, the ACS mandates a minimum entry altitude of 500 feet AGL. In strong wind conditions (15+ knots), consider higher entry altitudes to provide additional energy management options and account for increased descent rates.

Airspeed Management

The manufacturer’s recommended autorotation airspeed (typically 60-70 knots for most training helicopters) provides the best balance between forward speed and descent rate. This airspeed maintains rotor RPM while maximizing glide distance and energy available for the flare.

Flare and Landing Technique

The flare serves two purposes: trading forward speed for reduced descent rate and loading the rotor system with stored kinetic energy. Begin the flare at approximately 40-60 feet AGL, pulling aft cyclic to achieve a nose-high attitude. At 8-10 feet AGL, apply collective pitch to cushion the landing using stored rotor energy.

Risk Management Considerations

Entry Altitude: Never attempt practice autorotations below 500 feet AGL. Strong winds may require 700+ feet for adequate energy management.

Go-Around Decision: If the approach becomes unstable or landing parameters cannot be met, immediate go-around is mandatory. Forcing an unsafe landing violates both safety principles and ACS standards.

Landing Area Assessment: Continuously evaluate the landing area for obstacles, surface conditions, and wind effects. External factors requiring a go-around (livestock, vehicles, etc.) do not constitute unsatisfactory performance.

Safety Priority: Never sacrifice flight safety to complete the maneuver. A go-around executed for safety reasons demonstrates proper aeronautical decision-making.

Common Errors

• Late engine failure recognition (beyond 3 seconds)
• Failure to lower collective immediately
• Incorrect airspeed control
• Poor rotor RPM management
• Improper flare timing or technique
• Forcing an unsafe landing

Schedule

Equipment

Required References

• FAA-S-ACS-15 Private Pilot Helicopter ACS
• FAA-H-8083-21B Rotorcraft Flying Handbook
• Aircraft Flight Manual/Pilot’s Operating Handbook
• 14 CFR Part 91 (Operating Rules)

Materials

• Sectional chart of practice area
• Emergency procedures checklist
• Autorotation approach chart/diagram
• Performance planning worksheets

Visual Aids

• Rotor disk airflow diagram
• Height-velocity diagram
• Autorotation profile illustration

Instructor Actions

1. Brief the student on autorotation aerodynamics using the rotor disk airflow diagram to explain the driven, driving, and stall regions
2. Review the entry procedures emphasizing immediate collective lowering and anti-torque pedal application
3. Explain the minimum 500 feet AGL entry requirement and factors requiring higher altitudes
4. Demonstrate proper engine failure recognition timing (within 3 seconds) and immediate response
5. Show the student how to establish and maintain recommended autorotation airspeed using attitude control
6. Demonstrate rotor RPM management through collective pitch control during the descent
7. Explain flare timing and technique, emphasizing the energy management principles
8. Review go-around procedures and decision-making criteria for unsafe approaches
9. Perform a complete demonstration autorotation, narrating each phase and control input
10. Guide the student through their first practice autorotation with continuous coaching
11. Observe student performance and provide immediate feedback on technique and timing
12. Emphasize safety considerations throughout, including proper landing area assessment
13. Debrief each attempt focusing on areas for improvement and positive reinforcement

Student Actions

1. Review autorotation procedures in the aircraft flight manual before the lesson
2. Listen actively during the ground brief and ask questions about unclear concepts
3. Observe the instructor demonstration, noting control inputs and timing
4. Perform engine failure recognition within 3 seconds when prompted by instructor
5. Execute immediate autorotation entry by lowering collective and applying anti-torque pedal
6. Establish and maintain recommended autorotation airspeed throughout the descent
7. Monitor and maintain rotor RPM within normal operating limits using collective control
8. Assess landing area continuously for obstacles and safety concerns
9. Execute proper flare technique at appropriate altitude (40-60 feet AGL)
10. Apply collective pitch for touchdown cushioning using stored rotor energy
11. Maintain aircraft control throughout the maneuver including directional control
12. Make go-around decisions when approach parameters cannot be safely met
13. Accept instructor feedback and demonstrate improvement on subsequent attempts

Completion Standards

The student demonstrates competency in straight-in autorotation (FAA-S-ACS-15 PH.VI.B) when they can:

1. Engine Failure Recognition: Recognize simulated engine failure and initiate autorotation entry within 3 seconds
2. Entry Procedure: Immediately lower collective pitch and apply appropriate anti-torque pedal to maintain heading
3. Altitude Management: Maintain entry altitude of at least 500 feet AGL or higher as conditions require
4. Airspeed Control: Establish and maintain manufacturer’s recommended autorotation airspeed ±10 knots throughout descent
5. Rotor RPM Management: Keep rotor RPM within normal operating range using collective pitch control
6. Flare Execution: Initiate flare at appropriate altitude (40-60 feet AGL) with proper timing and control inputs
7. Landing Accuracy: Touch down within 200 feet of intended touchdown point
8. Touchdown Quality: Achieve smooth touchdown with minimal forward speed and descent rate
9. Directional Control: Maintain aircraft heading throughout the maneuver ±10 degrees
10. Safety Decisions: Demonstrate proper go-around decision-making when approach parameters cannot be safely met
11. Risk Assessment: Continuously evaluate landing area safety and external factors affecting the approach