Powerplant Failure at Altitude in a Single-Engine Helicopter

Objective

Upon completion of this lesson, the student will demonstrate the knowledge, risk management, and skills required for powerplant failure at altitude in a single-engine helicopter according to FAA-S-ACS-15 PH.VIII.B. The student will be able to identify appropriate entry conditions, execute a proper autorotation sequence, demonstrate energy management throughout the descent, and complete a power recovery at the appropriate altitude while maintaining aircraft control within ACS standards.

Content

Regulatory Foundation

Per 14 CFR 61.87(n), student pilots must receive training in emergency procedures including power failure situations. Commercial and private pilot training under 14 CFR 61.127 and 61.107 respectively mandate emergency procedure proficiency. This training directly supports 14 CFR 91.119 minimum safe altitude requirements and emergency landing procedures.

Principles of Autorotation

An autorotation is the helicopter’s equivalent of a glider’s best glide. When engine power is lost, the helicopter becomes an autogyro, with rotor rpm maintained by upward airflow through the rotor disc. The rotor system stores kinetic energy that can be converted to lift during the landing flare.

Think of autorotation like a maple seed falling from a tree - the spinning wing (rotor) creates lift and controls the descent rate. The key is managing this energy properly.

Energy Management Fundamentals

During autorotation, you’re managing three forms of energy:

• Potential energy: Aircraft altitude
• Kinetic energy: Forward airspeed
• Rotational energy: Rotor rpm

These energies are interconnected. Lower the collective to reduce drag on the rotor system, allowing rpm to increase. Adjust cyclic to maintain proper airspeed for your aircraft’s height-velocity diagram safe zone.

Autorotation Entry Sequence

Immediate Actions (Memory Items):

1. Lower collective - Reduce collective pitch to maintain rotor rpm
2. Enter autorotative glide - Establish proper airspeed per aircraft handbook
3. Check rotor rpm - Maintain within green arc (typically 90-110% Nr)

Follow-up Actions: 4. Attempt restart if altitude and time permit 5. Select landing area 6. Transmit emergency on 121.5 if time permits 7. Brief passengers 8. Secure aircraft systems

Airspeed Management

Reference your specific aircraft’s height-velocity (H-V) diagram. For most training helicopters like the R22, maintain 65-70 KIAS during autorotation to stay in the safe operating envelope. This airspeed provides:

• Maximum glide distance
• Adequate energy for flare
• Compliance with H-V diagram requirements

Energy Conversion During Flare

The flare converts forward airspeed into rotor energy and vertical lift. Begin the flare when you can identify individual surface features (typically 40-100 feet AGL depending on aircraft). Pull aft cyclic progressively to:

• Reduce forward airspeed
• Increase rotor rpm through energy transfer
• Reduce rate of descent

Risk Management Considerations

Altitude Requirements: Per ACS standards, practice autorotations must begin at minimum 1,000 feet AGL with power recovery completed by 500 feet AGL. This provides adequate safety margin for emergency procedures and prevents actual ground contact during training.

Location Considerations: Always practice over suitable landing areas. Consider:

• Wind direction and velocity
• Surface conditions
• Obstacles in approach path
• Emergency landing site availability

Airspeed and Energy State: Maintaining proper airspeed keeps the helicopter in the safe portion of the H-V diagram. Too slow creates a dangerous situation if actual power failure occurs. Too fast reduces autorotation efficiency and increases landing loads.

Common Errors

• Late collective reduction: Delays entry, causes rotor rpm decay
• Improper airspeed: Either too fast (reduces efficiency) or too slow (H-V concern)
• Inadequate rotor rpm monitoring: Allows rpm to decay below minimum
• Premature or late flare: Affects landing energy management
• Overcontrolling: Causes aircraft oscillations during critical phase

Power Recovery Procedures

Recovery must be smooth and positive:

1. Smoothly raise collective while adding power
2. Adjust cyclic to arrest descent and maintain airspeed
3. Return to normal flight attitude
4. Monitor engine parameters during power application

Schedule

Equipment

Required References

• FAA-H-8083-21B Helicopter Flying Handbook (Chapter 11)
• FAA-S-ACS-15 Private Pilot Helicopter ACS
• Aircraft Flight Manual/Pilot’s Operating Handbook
• Height-Velocity diagram for specific aircraft
• Emergency checklist

Materials and Visual Aids

• Whiteboard for energy management diagrams
• Aircraft H-V diagram poster or handout
• Training helicopter with appropriate emergency equipment
• Radio for emergency frequency practice

Instructor Actions

1. Brief student on lesson objectives and review autorotation theory using energy management diagrams on whiteboard
2. Demonstrate proper H-V diagram interpretation specific to training aircraft, emphasizing safe operating envelope
3. Review emergency checklist procedures and memory items for powerplant failure
4. Conduct pre-flight briefing covering altitude requirements, recovery procedures, and safety protocols
5. Demonstrate complete autorotation sequence from 1,000+ feet AGL, narrating each step of collective reduction, airspeed establishment, and energy management
6. Show proper rotor rpm monitoring throughout the descent, pointing out green arc limits and energy indicators
7. Demonstrate flare timing and technique at approximately 500 feet AGL, explaining energy conversion principles
8. Execute smooth power recovery while maintaining aircraft control and explaining collective/cyclic coordination
9. Coach student through first practice attempt, providing immediate feedback on collective timing and airspeed control
10. Guide subsequent practice iterations, focusing on consistency and addressing specific technique deficiencies
11. Debrief each attempt immediately after power recovery, highlighting successful elements and areas for improvement
12. Conduct post-flight analysis of overall performance against ACS standards

Student Actions

The student will:

1. Participate actively in ground briefing, asking questions about autorotation theory and emergency procedures
2. Study H-V diagram for the training aircraft and identify safe operating parameters
3. Verbalize understanding of altitude requirements and safety protocols before flight
4. Observe CFI demonstration carefully, taking mental notes of timing and control inputs
5. Practice autorotation entries beginning at minimum 1,000 feet AGL with smooth, deliberate collective reduction
6. Maintain proper airspeed throughout descent according to aircraft specifications
7. Monitor rotor rpm continuously and make collective adjustments to keep within green arc
8. Execute power recoveries smoothly at or above 500 feet AGL using coordinated control inputs
9. Self-evaluate performance after each practice attempt, identifying areas for improvement
10. Ask specific questions about technique or theory during practice sessions
11. Demonstrate consistent technique across multiple practice iterations

Completion Standards

The student demonstrates satisfactory performance when they can consistently accomplish the following elements according to FAA-S-ACS-15 PH.VIII.B:

Knowledge Requirements

• Explain autorotation aerodynamics including energy management principles and rotor behavior during power-off flight
• Identify proper entry procedures including memory items and follow-up actions per aircraft checklist
• Describe H-V diagram limitations and explain how airspeed selection affects emergency landing capability

Risk Management Requirements

• Initiate autorotation practice only at minimum 1,000 feet AGL over suitable landing areas
• Complete power recovery at or above 500 feet AGL maintaining positive aircraft control
• Select appropriate airspeeds that maintain helicopter within safe H-V envelope throughout maneuver

Skill Requirements

• Enter autorotation within 2 seconds of simulated power failure with immediate collective reduction
• Maintain rotor rpm within manufacturer’s specified limits (typically ±10% Nr)
• Establish and maintain appropriate airspeed ±5 knots of target speed for aircraft type
• Execute smooth power recovery at appropriate altitude without altitude loss exceeding 100 feet
• Demonstrate coordinated flight controls throughout maneuver without adverse yaw or excessive control inputs

Performance meets standards when student can complete 3 consecutive autorotations demonstrating all required elements within specified tolerances while maintaining aircraft control and following proper procedures throughout the sequence.