1. Managing Rotorcraft Safety During Frequently Performed Unique Missions September 28, 2005 AHS International Helicopter Safety Symposium 2005 Philip G. Potts Chief System Engineer – Safety / Airworthiness Sikorsky Aircraft Corporation

2. 2 Investigation Premise Maintaining Fleet Airworthiness Presumes: Aircraft Operate within Certified Mission Profiles Some Unique Missions Regularly Expect: Aircraft to Repeatedly Perform At or Beyond Certified Limitations Frequent Short Distance Sorties at Maximum Performance Argument Unique Maximum Performance Missions, Increase Potential to Degrade Fleet Safety and Compromise Structural Fatigue Lives, Long Term AHS International Helicopter Safety Symposium 2005

3. 3 Investigation Documents Overview Fixed Wing Aircraft and Rotorcraft Accident Reports Arial Fire Fighting: Assessing Safety and Effectiveness Harsh Mission Environment Dominates Mishap Causes Fatigue of Primary Structure Caused Aircraft Mishaps US Civil Rotorcraft Accidents – Twin Turbine Mechanical Failures Dominated Mishap Causes Fatigue of Primary Drive Structure is a Significant Cause of Rotorcraft Mishaps AHS International Helicopter Safety Symposium 2005

4. 4 Aerial Fire Fighting Cause Summary Heavy Transport Fleet Mission Loads ‘The severity of the maneuver loads experienced by airplanes involved in firefighting operations’ ‘exceeded both the maneuver limit and ultimate load factors’ Structural Fatigue ‘These repeated and high-magnitude maneuvers and the repeated exposure to a turbulent environment hasten the initiation of fatigue cracking and increase the growth rate of cracking once it exists.’ Airworthiness Risk ‘…fatigue cracking and accelerated crack propagation can and should be addressed through maintenance programs.’ Conclusion: ‘…no effective mechanism currently exists to ensure the continuing airworthiness of these firefighting aircraft.’ AHS International Helicopter Safety Symposium 2005

5. 5 US Civil Rotorcraft Cause Summary Twin Turbine Fleet Structural Fatigue ‘Past design standards are inadequate relative to the many new and varied activities’ Mission Loads ‘Pilots did exceed design limits’ Airworthiness Risk ‘required and timely maintenance was skipped’ ‘…less than thorough inspections were performed,’ Conclusion: ‘The current fleet appears, broadly speaking, to be underdesigned in view of today's commercial usage’ AHS International Helicopter Safety Symposium 2005

6. 6 Report Conclusions Load Characterizations Helicopter: ‘Underdesigned’ Firefighting: ‘High magnitude maneuvers’ Responsibility to Airworthiness ‘Inadequate maintenance procedures to detect fatigue cracking’ Operators ‘did not possess engineering expertise’ ‘to predict the effects of those stresses on the operational life of the airplanes’ No Coordinated Management of Responsible Process Owners Pilot, Operator, OEM, Maintenance, Regulator AHS International Helicopter Safety Symposium 2005

7. 7 Report Conclusions in Question Process Owners Limitations Certification Standards Are Standards followed? Anticipate Mission Changes? Maintenance Inspection Procedures Not Directly Tied to Unique Missions How Does (Do): Operators Achieve Operational Safety with Limited Technical Awareness of Mission Performance OEM Collect Technical Information for Unique Missions Pilot Safely Operate to Unique Mission Parameters AHS International Helicopter Safety Symposium 2005

8. 8 Operating Standards No Measurement Requirements Airplane Firefighting Mission Measurements Certified Limit and Ultimate Loads were Regularly Exceeded An Airframe Manufacturer Analyzed a ‘5 to 7 Time’ Usage Acceleration during Firefighting Civil Helicopter Accidents Distribution Dynamic System Mechanical Failure Rate  OF 302 Total Twin Turbine Accidents (29%) 89 Dynamic System +(13%) 39 Engine  Fatigue is 42% of the ‘Cause’ Total  This Rate is Equivalent to Single Turbine Accidents, by % AHS International Helicopter Safety Symposium 2005

9. 9 Airworthiness A Manual Method Airframe Methodology …’visual inspections for cracks’ Pilots Enjoy Challenging Missions Operators Not Prepared to Analyze Unique Missions Effects Rotorcraft Fatigue Lives Derive from Mission Loads, Frequencies, and Material Strength Dynamic System Cracks are Very Small with Very Short Inspection Intervals Process Gap: Unique Missions Cause Significant Variations in Load Patterns and Frequency Maintenance Intervals Not Tracked to Unique Missions Changes ‘Visual Crack Inspection Methodology’ is Impractical for Rotorcraft AHS International Helicopter Safety Symposium 2005

10. 10 Investigation Findings Characteristics That Affect Safety Unique Operations Are Rarely Standard Unique Missions Potentially Increase Loading or Frequencies Fatigue Lives Degraded by Unique Mission Cycles Maintenance Inspections are Based on Certified Mission Maintenance Schedules not directly Linked to Mission Frequencies Airframe Visual Inspection Methodology Does Not Apply to Rotorcraft System Safety Airworthiness Requires an Automated Data Source Technical Data Needed Mission Flight Loads Require Quantified Mission Inspection Intervals Crack Growth and Fatigue Lives Affected by Increased Loads An Improved Way of Evaluating Missions is Required. AHS International Helicopter Safety Symposium 2005

11. 11 Recommendations Automate Mission Management Monitor Mission Uncertainties for Rotorcraft Drive System 1. Significant Torque and Frequency Events  Alert Operator & OEM of Potential System Life Degradation  Assess Pilot Techniques for Mission  Adjust Maintenance and Inspection Intervals to Unique Mission Conditions Dynamic Monitoring of Tail Drive System: 2. Add Vibration and Thermal Monitoring to Primary Drive Shaft Components AHS International Helicopter Safety Symposium 2005

12. 12 Backup

13. 13 Helicopter Accident Data Civil Twin Turbine Helicopter Fatigue represents 42 % of Dynamic System Failures Issue: ‘The current fleet appears …to be underdesigned in view of today’s commercial usage.’ AHS International Helicopter Safety Symposium 2005

14. 14 Helicopter Accident Data Civil Twin Turbine Helicopter Mechanical Failures Represent 42% of Fleet Accidents (29%) 89 Dynamic System +(13%) 39 Engine AHS International Helicopter Safety Symposium 2005

15. 15 Fatigue – Elements of Life Analysis [2] Fatigue Strength Curve [1] Measured Flight Loads 1 1.Flight loads 2.Material Strength of the Component 3.Frequency and duration of all maneuver loads [3] Life in Load Cycles Lower Loads Higher Fatigue Life