Dynamic Rollover

Objective

Upon completion of this lesson, the student will be able to identify the factors that contribute to dynamic rollover, recognize conditions conducive to dynamic rollover, and demonstrate preventive flight techniques to avoid this hazardous condition during ground operations and slope landings as required by FAA-S-ACS-15 PH.VIII.H.

Content

Definition and Elements of Dynamic Rollover (PH.VIII.H.K1)

Dynamic rollover is an uncommanded rolling tendency that can develop when one skid or wheel of the helicopter contacts the surface while the aircraft is still producing lift. Unlike static rollover, which occurs when the aircraft’s center of gravity moves outside the critical angle while at rest, dynamic rollover involves the interaction of lift, pivot point, and lateral forces that can rapidly accelerate the aircraft beyond the point of no return.

The critical elements include:

• A pivot point (one skid, wheel, or obstruction)
• Continued lift production from the rotor system
• Lateral displacement of thrust vector or center of gravity
• Insufficient opposing control input to arrest the rolling motion

Think of dynamic rollover like a teeter-totter with one end stuck to the ground - the longer end will rapidly accelerate downward unless you apply immediate corrective force.

Interacting Factors Contributing to Dynamic Rollover (PH.VIII.H.K2)

Thrust and Power Settings: Higher power settings increase the upward force acting through the rotor mast. When combined with a pivot point, this creates a longer moment arm for the rolling force.

Crosswind Effects: Crosswinds require cyclic input to maintain position, which tilts the rotor disc and thrust vector laterally. A quartering tailwind is particularly hazardous as it combines translating tendency with crosswind effects.

Slope Operations: Landing upslope or downslope changes the aircraft’s relationship to gravity and affects the critical rollover angle. Downslope landings are especially dangerous because the downhill skid contacts first, creating an immediate pivot point.

Lateral Center of Gravity: Passengers, cargo, or fuel imbalances shift the CG laterally. An off-center CG reduces the critical rollover angle and makes the aircraft more susceptible to dynamic rollover.

Aircraft Weight: Heavier aircraft require more power to hover, increasing the vertical force component. However, weight also provides greater inertia that can work for or against recovery efforts.

Flight Control Position: Improper cyclic positioning, particularly holding lateral cyclic away from the pivot point, accelerates the rollover. Recovery requires immediate cyclic input toward the rising skid.

Preventive Flight Techniques and Recovery (PH.VIII.H.K3)

Prevention During Normal Operations:

• Maintain balanced loading within CG limits per 14 CFR 91.9
• Use proper crosswind landing techniques
• Avoid sideward flight near the surface
• Ensure adequate landing area clearance
• Make positive, deliberate control inputs

Slope Landing Prevention:

• Limit slope operations to manufacturer specifications (typically 15-20 degrees)
• Land perpendicular to slope direction when possible
• Use running landings on steep slopes rather than hovering approaches
• Maintain light skid contact initially

Recovery Technique:

1. Immediate cyclic input toward the rising skid - This is the critical first action
2. Lower collective to reduce lift and eliminate the pivot point
3. Add power only after achieving lateral control if still airborne
4. Do not attempt to lift off once rollover has begun - this typically makes the situation worse

The window for successful recovery is extremely narrow - typically less than 2 seconds. Prevention is always preferable to recovery.

Surface Conditions Conducive to Dynamic Rollover (PH.VIII.H.R1)

High-Risk Surfaces:

• Uneven terrain with rocks, logs, or debris
• Soft surfaces like mud, sand, or snow that allow skid penetration
• Slippery surfaces that reduce skid friction
• Surfaces with lateral slope
• Confined areas with obstacles that can catch skids

Assessment Techniques:

• Conduct thorough reconnaissance of landing areas
• Look for uniform, firm surfaces
• Avoid areas with visible obstructions
• Consider recent weather effects on surface conditions

Landing Gear Proximity to Obstructions (PH.VIII.H.R2)

During low hover operations, maintain awareness of:

• Curbs, rocks, or debris near skid positions
• Uneven pavement or concrete joints
• Parking blocks or tie-down hardware
• Snow banks or vegetation that can catch skids

Maintain at least skid-width clearance from any obstruction when hovering low. Higher hover heights eliminate this risk but create other hazards like loss of translational lift and increased power requirements.

Flight Control Inputs During Takeoff and Landing (PH.VIII.H.R3)

Critical Input Errors:

• Lateral cyclic held away from contacted skid
• Abrupt or excessive control movements
• Premature collective application during recovery
• Inadequate cyclic authority due to aft CG or high density altitude

Proper Technique:

• Smooth, deliberate control inputs
• Maintain cyclic in neutral lateral position during surface contact
• Immediate corrective action if skid contact becomes uneven
• Ensure adequate cyclic authority before attempting slope operations

Sideward Hover Risks (PH.VIII.H.R4)

Sideward hovering flight near the surface creates multiple dynamic rollover hazards:

• Translating tendency pushes the aircraft toward obstacles
• Pendulum effect can develop if the aircraft contacts an obstruction
• Reduced control response at low airspeeds
• Visual illusions make it difficult to maintain precise control

Limit sideward flight to operational necessity and maintain adequate altitude and clearance from obstacles.

Aircraft Slope Limitations (PH.VIII.H.R5)

Consult the Rotorcraft Flight Manual (RFM) for specific slope limitations, typically:

• Static slope limit: 15-20 degrees maximum
• Dynamic slope limit: Often less than static due to control margins needed
• Lateral CG considerations: Reduced slope capability with off-center loading
• Density altitude effects: Reduced performance may further limit slope capability

Per 14 CFR 91.9, operations must remain within approved limitations. Exceeding slope limits violates both regulations and safe operating practices.

Critical Rollover Angle and Rolling Moment (PH.VIII.H.R6)

The critical rollover angle varies by aircraft type but typically ranges from 8-15 degrees of lateral tilt. Beyond this angle, the center of gravity moves outside the base of support, making rollover inevitable.

Factors Affecting Critical Angle:

• Skid width relative to aircraft height
• CG position within allowable range
• Rotor mast height and thrust vector location
• Surface conditions and skid penetration

Once the rolling moment exceeds the aircraft’s ability to generate opposing cyclic moment, recovery becomes impossible. This is why immediate recognition and response are essential.

Translating Tendency and Dynamic Rollover (PH.VIII.H.R7)

Translating tendency (lateral drift due to tail rotor thrust) interacts with dynamic rollover in several ways:

• Pushes aircraft toward obstructions during hover operations
• Creates lateral loading on skids during surface contact
• Requires corrective cyclic input that can become a pivot point contributor
• Combines with crosswind effects to create complex control requirements

Anti-torque pedal inputs affect translating tendency direction and magnitude. Proper power management and wind awareness help minimize these effects.

Regulatory Considerations

14 CFR 91.9 - Aircraft operating limitations must be observed, including slope limits 14 CFR 91.13 - Careless and reckless operation prohibitions apply to dynamic rollover scenarios 14 CFR 91.103 - Preflight planning must include landing area assessment

Schedule

Equipment

Required References:

• FAA-H-8083-21B Helicopter Flying Handbook, Chapter 11
• FAA-S-ACS-15 Private Pilot Helicopter Airman Certification Standards
• Aircraft-specific Rotorcraft Flight Manual (RFM)
• 14 CFR Parts 91 (current edition)

Visual Aids:

• Dynamic rollover demonstration model or tablet simulation
• Slope angle measurement tool (inclinometer)
• Center of gravity diagram charts
• Surface condition assessment photographs
• Video examples of dynamic rollover scenarios (if available)

Materials:

• Whiteboard or flip chart for force vector diagrams
• Weight and balance calculation worksheets
• Emergency procedure checklist

Instructor Actions

1. Open the lesson by demonstrating dynamic rollover physics using a model helicopter or simple pivot demonstration, explaining how lift plus pivot point equals rapid acceleration

2. Define dynamic rollover clearly, distinguishing it from static rollover and emphasizing the time-critical nature of the event

3. Present the contributing factors systematically, using specific aircraft examples and power calculations to show thrust vector effects

4. Demonstrate center of gravity calculations showing how lateral CG shifts affect critical rollover angles using the aircraft’s actual weight and balance data

5. Explain crosswind effects using diagrams showing how quartering winds combine translating tendency with crosswind drift to create hazardous conditions

6. Review slope limitations from the aircraft RFM, calculating actual slope angles using an inclinometer and relating them to published limits

7. Walk through surface assessment techniques, showing photographs of good versus poor landing surfaces and discussing recognition criteria

8. Present the recovery procedure step-by-step, emphasizing the immediate cyclic-toward-rising-skid input and collective reduction sequence

9. Discuss real-world scenarios including dynamic rollover accidents and their contributing factors, relating lessons learned to prevention techniques

10. Address regulatory requirements under 14 CFR 91.9 and 91.103, showing how dynamic rollover prevention fits into legal operating requirements

11. Quiz the student on recognition criteria, contributing factors, and recovery procedures to assess comprehension

12. Assign homework to review RFM slope limitations and practice weight and balance calculations with various loading scenarios

Student Actions

During Lesson Presentation:

• Take notes on critical rollover angles and contributing factors
• Ask questions about specific scenarios or aircraft limitations
• Participate in force vector discussions and calculations
• Practice identifying surface hazards from photographs

Demonstrate Understanding by:

• Explaining the physics of dynamic rollover using proper terminology
• Calculating weight and balance effects on rollover susceptibility
• Identifying high-risk surface conditions and operational scenarios
• Describing the proper recovery sequence with correct timing emphasis
• Discussing prevention techniques for various operational situations

Complete Practice Problems:

• Weight and balance scenarios with lateral CG variations
• Slope angle calculations using inclinometer readings
• Surface condition risk assessments from provided scenarios
• Decision-making exercises for go/no-go determinations

Completion Standards

The student demonstrates understanding of dynamic rollover per FAA-S-ACS-15 PH.VIII.H when they can:

Knowledge Standards (PH.VIII.H.K1-K3):

• Define dynamic rollover including the three essential elements: pivot point, lift, and lateral force displacement
• Identify all contributing factors including thrust magnitude, crosswind direction and velocity, surface slope angle, lateral CG position, aircraft weight, and control input direction
• Explain preventive techniques including surface assessment criteria, slope limitation adherence, proper control technique, and balanced loading procedures
• Describe recovery procedures with emphasis on immediate cyclic input direction, collective reduction timing, and decision criteria for recovery attempts

Risk Management Standards (PH.VIII.H.R1-R7):

• Assess surface conditions identifying uneven terrain, soft surfaces, slopes, and obstruction hazards with 100% accuracy on presented scenarios
• Recognize obstruction hazards during low hover operations, maintaining awareness of landing gear clearance requirements
• Demonstrate proper control input knowledge explaining the hazards of lateral cyclic displacement and improper recovery technique
• Explain sideward hover risks including translating tendency effects, pendulum forces, and altitude considerations
• State aircraft slope limitations accurately from RFM data and explain factors that reduce operational slope capability
• Calculate critical rollover angles and explain factors affecting rolling moment development
• Describe translating tendency interaction with dynamic rollover scenarios and prevention techniques

Performance Standards:

• Completes oral examination covering all knowledge and risk management elements with no errors on safety-critical items
• Demonstrates scenario analysis correctly identifying dynamic rollover risks in 5 of 5 presented operational situations
• Explains recovery procedures in proper sequence with correct emphasis on timing and control input direction

The lesson is complete when the student can consistently identify dynamic rollover hazards, explain prevention techniques, and describe proper emergency procedures without prompting or reference materials.