Dynamic Rollover

Objective

The CFI candidate will demonstrate the ability to teach dynamic rollover to a student pilot by explaining the aerodynamic and physical forces involved, identifying contributing factors and risk conditions, demonstrating preventive techniques and recovery procedures, and evaluating student understanding through effective questioning and assessment techniques, meeting the standards outlined in ACS task HI.XIII.I.

Content

Dynamic Rollover Fundamentals

Dynamic rollover is a critical hazard unique to helicopters that occurs when the helicopter pivots laterally around the landing gear, tire, or skid in contact with the surface. Unlike static rollover (which happens slowly), dynamic rollover develops rapidly and can result in catastrophic aircraft damage or destruction.

The Physics of Dynamic Rollover Think of dynamic rollover like a teeter-totter that suddenly tips past its balance point. Once the helicopter’s center of gravity moves beyond the pivot point created by the landing gear, gravity takes over and the aircraft rapidly accelerates toward the ground. The key difference is that helicopter rotors continue producing lift throughout this process, which can actually accelerate the rollover rate.

Critical Angle Every helicopter has a critical rollover angle - typically between 5-17 degrees depending on the aircraft type. Once this angle is exceeded, recovery becomes impossible with normal flight control inputs. This is why prevention is absolutely critical.

Contributing Factors and Interactions

Primary Contributing Factors:

1. Lateral Center of Gravity - Heavy loads on one side create an initial rolling moment
2. Crosswinds - Create lateral forces that must be countered with cyclic input
3. Slope Operations - Ground slope effectively reduces the critical rollover angle
4. High Power Settings - Increase the forces transmitted through the rotor system
5. Sudden or Excessive Control Inputs - Can initiate the rollover sequence
6. Aircraft Weight - Heavier aircraft have more momentum once rollover begins

Factor Interactions: These factors compound each other. For example, a helicopter with a laterally shifted CG operating on a slope in crosswind conditions requires significant cyclic input to maintain level attitude. If the pilot makes an abrupt control input or encounters a wind gust, the combination can exceed the critical angle threshold.

The relationship between thrust and dynamic rollover is particularly important. Higher power settings increase the forces transmitted through the rotor system to the fuselage. When combined with lateral cyclic input, these forces can create significant rolling moments around the ground contact point.

Risk Management and Surface Conditions

High-Risk Surface Conditions:

• Slopes greater than 15 degrees
• Uneven or soft surfaces that allow one landing gear to sink
• Surfaces with debris that can catch landing gear
• Wet or icy surfaces reducing friction
• Rocky or irregular terrain creating unstable contact points

Landing Gear Proximity Hazards: During low-altitude hover operations, be constantly aware of:

• Proximity to obstacles that could snag landing gear
• Surface irregularities that could create pivot points
• Changes in surface firmness that could cause differential gear contact

Preventive Flight Techniques

Slope Operations:

1. Always land and takeoff perpendicular to the slope when possible
2. Use minimum power necessary for the operation
3. Make slow, deliberate control inputs
4. Maintain light skid/gear contact during slope operations
5. Plan escape routes before committing to slope landings

General Prevention:

• Maintain awareness of wind conditions and direction
• Keep lateral CG within limits
• Use smooth, gradual control inputs during ground operations
• Monitor power requirements - excessive power may indicate developing problems
• Maintain situational awareness of surface conditions

The “Light on the Skids” Technique: During slope operations, maintain just enough collective to keep the aircraft light on the landing gear. This reduces the pivot force while maintaining control authority. Think of it as “dancing” on the surface rather than sitting firmly.

Recovery Techniques

If Dynamic Rollover is Detected: The key is early recognition - once past the critical angle, recovery is impossible.

Early Stage Recovery (still recoverable):

1. Immediately lower collective to reduce thrust
2. Apply opposite cyclic to counter the roll
3. Use coordinated control inputs - don’t fight the controls
4. If unsuccessful, continue lowering collective and prepare for emergency landing

Late Stage (past critical angle):

1. Immediately reduce collective to minimize damage
2. Turn off fuel and electrical systems if time permits
3. Brace for impact
4. Execute emergency shutdown after impact

The harsh reality is that late-stage dynamic rollover is generally not recoverable. This emphasizes why prevention and early recognition are so critical.

Common Errors

1. Overcontrolling - Making excessive or abrupt cyclic inputs that initiate rollover
2. Ignoring Environmental Conditions - Failing to account for wind, slope, or surface conditions
3. Improper Slope Technique - Landing parallel to slopes or using excessive power
4. Poor CG Management - Operating with lateral CG shifts without compensation
5. Delayed Recognition - Failing to recognize early signs of developing rollover
6. Improper Recovery Technique - Attempting to recover when past the critical angle
7. Inadequate Pre-flight Planning - Not considering rollover risks during mission planning

Teaching Considerations

When teaching dynamic rollover, emphasize that this is a “no-warning” emergency that develops rapidly. Use analogies like the teeter-totter to help students understand the physics. Stress that prevention through proper technique and risk assessment is the only reliable defense.

Schedule

Equipment

Required References:

• FAA-H-8083-21A Rotorcraft Flying Handbook (Chapter 11)
• FAA-H-8083-4 Helicopter Instructor’s Handbook
• Aircraft-specific Flight Manual/POH
• FAA-S-ACS-29 Helicopter Instructor Rating ACS

Visual Aids:

• Dynamic rollover diagram showing critical angle
• Whiteboard for force vector illustrations
• Model helicopter for demonstration
• Video examples of dynamic rollover incidents (if available)
• Photos of various surface conditions and hazards

Materials:

• Slope operations checklist
• Emergency procedures quick reference
• Dynamic rollover decision tree

Instructor Actions

The CFI candidate will:

1. Present the lesson using clear explanations and appropriate analogies to explain dynamic rollover physics and the concept of critical angles
2. Demonstrate teaching techniques by using visual aids, diagrams, and model aircraft to illustrate force vectors and rollover mechanics
3. Identify and explain all contributing factors (thrust, crosswind, slope, lateral CG, weight) and their interactions using specific examples
4. Teach prevention techniques including proper slope operations, control input techniques, and environmental assessment
5. Explain recovery procedures while emphasizing the critical importance of early recognition and the reality of non-recoverable situations
6. Identify common student errors and demonstrate corrective teaching techniques
7. Conduct effective knowledge assessment using scenario-based questions and practical applications
8. Demonstrate risk management instruction by teaching hazard identification and mitigation strategies

Student Actions

The student (evaluator acting as student) will:

1. Listen actively and ask relevant questions about dynamic rollover concepts
2. Participate in discussions about contributing factors and their interactions
3. Identify risk factors when presented with various scenario descriptions
4. Demonstrate understanding by explaining prevention techniques in their own words
5. Respond to scenario questions about proper procedures and decision-making
6. Ask clarifying questions about recovery procedures and limitations
7. Participate in knowledge assessment by answering questions and solving problems
8. Demonstrate comprehension through practical application exercises

Completion Standards

The CFI candidate successfully completes this task when they demonstrate the ability to teach dynamic rollover concepts and procedures according to ACS standards HI.XIII.I. The candidate must:

Knowledge Standards:

• Accurately explain the elements related to dynamic rollover including physics, critical angles, and rollover mechanics (HI.XIII.I.K1)
• Clearly describe the interactions between thrust, crosswind, slope, lateral CG, aircraft weight, and flight controls that contribute to dynamic rollover (HI.XIII.I.K2)
• Effectively teach preventive flight techniques and recovery procedures for all flight operations including slope operations (HI.XIII.I.K3)
• Identify and explain common errors related to dynamic rollover and demonstrate corrective teaching techniques (HI.XIII.I.K4)

Risk Management Standards:

• Teach identification of surface conditions conducive to dynamic rollover and appropriate risk mitigation strategies (HI.XIII.I.R1)
• Demonstrate instruction on landing gear proximity hazards to obstructions during low altitude hover operations (HI.XIII.I.R2)

Teaching Effectiveness Standards:

• Use appropriate instructional techniques including visual aids, analogies, and practical examples
• Conduct effective knowledge assessment through questioning and scenario evaluation
• Demonstrate ability to identify and correct student misconceptions
• Present information in a logical, organized sequence that promotes learning retention
• Maintain appropriate instructor demeanor while covering this critical safety topic