Presentation at 7 th Annual Wildland Fire Safety Summit, Toronto, Ontario, Canada 19th July,2003

1. THE SAFE AND ECONOMIC STRUCTURAL HEALTH MANAGEMENT OF AIRTANKER AND LEAD AIRCRAFT INVOLVED IN FIREBOMBING OPERATIONS Presentation at 7th Annual Wildland Fire Safety Summit, Toronto, Ontario, Canada 19th July,2003 Steve Hall (Celeris Aerospace Canada Inc.) Dick Perry (Sandia National Laboratory) Joe Braun (Systems and Electronics Inc.)

2. OVERVIEW • Reasons for Structural Concerns Related to Aircraft Operating in the Firebombing Role • Potential causes of structural problems • Addressing the Structural Concerns • Rationale behind the procedures and processes that need to be implemented with particular reference to fatigue and damage tolerance • Understanding the loads imposed on firebombing aircraft • Structural Health Management of Aircraft Involved in the Firebombing Role • Short and longer term issues related to the safe and economic use of these aircraft • Inspection, Maintenance and the Bottom Line • Accumulating Knowledge • Pending Activities • Conclusions and Recommendations

3. C-130A Built 1957 21,900 hours total Both wings failed June 2002 PB4Y-2 Single Tail Liberator Built 1944/45 timeframe 8,200 Special Mission hours Failure one wing July 2002 SUMMER 2002 WING FAILURES

4. REASONS FOR CONCERN • Resulted in the formation of the Blue Ribbon Commission by the USDA/FS and BLM which reported in December 2002 • Number of recommendations/observations including • Many of the aircraft involved in the firebombing role were not designed for this role • Loads to which they have been subjected are largely unknown as is their current structural health status • There is a need to harmonize the inspection and maintenance of firebombing aircraft with modern day certification approaches such as fatigue and damage tolerance • Approach to funding, contracts and the ongoing and modernization of the fleet needs to be reviewed

5. ADVERSE OPERATIONAL IMPLICATIONS • C-130A and PB4Y-2 Fleets immediately grounded • Loss of approx 10-12 Heavy Tankers • Major concerns about USDA/FS Beech Baron Lead Aircraft • Immediate need for replacement? • Forest Service note that contracts will not be awarded to C-130A and PB4Y-2 aircraft • Heavy airtankers operating with a 15% reduction in payload for the 2003 fire season • Unanticipated expenses associated with additional inspection and maintenance actions • Delayed contract award and operational availability

6. OVERVIEW OF FIREBOMBING AIRCRAFT CONFIGURATIONS AND OPERATIONS

7. FIREBOMBING AIRCRAFT • Air Tankers • 800 – 1,200 gallons • Translates to approximately 8,000 to 12,000 lbs • Heavy Air Tankers • 2,200 – 3,000 gallons and above • Translates to approximately 22,000 to 30,000 lbs retardant

8. FIREBOMBING AIRCRAFT (cont) • Lead Aircraft • Initial Survey of Fire for Escape Routes • Guide Heavy Tankers in over fire • Ensure Fire Prevention Officer has view of drop • Spend far more time over the fire than do the air tankers

9. Internal Tank External Tank Scoop AIR TANKER CONFIGURATION

10. Constant Flow One pair doors Computer controlled Aperture changes to ensure constant flow Consistent “Coverage Level” Sequenced Doors Two, four, eight or more Door sequence automatically selected Release percentage of load that is proportional to the number of doors Coverage Level not as consistent TYPES OF TANK

11. TYPES OF LOAD • Retardant or Foam • Pre-mixed or mixed on board • Drop as a barrier to the fire • Water • Dropping on the fire

12. OPERATIONAL PROFILE AIR TANKERS • Transit to fire • Depends on distance, if relatively close often below 2000 ft AGL • Holding pattern around the fire • Generally around 1,000 ft to 1,500ft around the fire • Drop Zone • 150 ft AGL (or 150ft parallel to terrain in mountainous drops) • Airspeed around 110 – 120 knots • Flap often required (typically 50%, occasionally 100%) • Want available power when retracted • Load, usually dropped in 50% increments, occasionally 100% • Drop Time • Of the order of 4 -10 seconds depending on coverage level

13. Potential Causes of Structural Problems

14. SPECIAL MISSION AIRCRAFT • Aircraft that is operating in a role for which was not envisaged during its design • Firebombing Aircraft • ILS/VOR Calibration • Pipeline/Geological Survey • Crop-Spraying • Atmospheric Research (Hurricane Hunters) • Majority tend to operate in Low-level roles • Low-level consistent use below 2,500 ft AGL • Turbulent environment aircraft subject to an increased gust frequency • Some roles involve increased manoeuvre spectrum for terrain avoidance • Note that even when an aircraft has been designed for the environment, care is required regarding the source of the design loads • Lots of data for low-level data is transit data and is not usually representative of consistent low-level operation Low-level Roles High-Level Role

15. WHAT DO WE KNOW ABOUT SPECIAL MISSION SPECTRUM? • Generally very little • Limited number of health monitoring programs completed to define the loads • NRCC/IAR Circa Mid 1970’s - 1988 • Limited NASA Work (Reliability Issue) • FAA Collecting Low-level data, yet to be collated • However, from the limited data available some initial trends have been identified which indicate an urgent need for further work

16. LOADING MECHANISMS • Two mechanisms that have to be considered • High Load Exceedance or Overstressing the aircraft • Over-g of the aircraft • High Load at High Weight Concerns • Long-term impact of cyclic loading • Fatigue and Damage Tolerance • Repetitions of cyclic loading and its accumulated impact • A major focus of past analyses of special mission aircraft has been the high load exceedance aspects • Part of the picture and something of which we have to be constantly vigilant • However, it is by no means the full picture, nor the major reason for the structural failures that have occurred

17. Exceedances/Hour (Log) -ve Spectrum +ve Spectrum Increasing Severity Increasing Severity G-Level 1.0g IDENTIFYING HARSH OR UNUSUAL USAGE

18. COMPARATIVE SEVERITY

19. F-27 DATA – SAMPLE 003

20. F-27 DATA – SAMPLE 004

21. FATIGUE CONCEPTS Alt Stress (Sa) Max Stress (Smax) Stress Alternating Stress (Sa) Sa1 Mean Stress (Sm) Min Stress (Smin) Different Mean Stress Levels (Sm) N1 Time Number of Cycles (N) Miner’s Cumulative Damage Law Smin Smax R =

22. MAIN OBSERVATIONS • Aircraft in Low-level Special Mission Roles see a much more severe spectrum than comparable aircraft operating in the roles for which they were originally designed • Inordinate amount of relatively low-level loads • Much more turbulent environment • More Manoeuvres • Control Aircraft • Terrain avoidance • Some high loads, but generally the majority of the structural damage can be attributed to the low level loads • A large amount of accumulated world-wide flying in the original design role is a necessary, but not a sufficient condition for ongoing structural integrity in the special mission role • Acceleration of damage in critical areas • Damage being sustained in previously unknown areas

23. ADDRESSING THE STRUCTURAL CONCERNS

24. SO WHAT? • The previous slides have illustrated that the limited data available suggests that from a cyclic loading perspective (fatigue) firebombing usage is more severe than many operational roles, including the roles for which the majority of the aircraft were designed • The next issue that has to be addressed is what are the implications of these loads for individual aircraft structures?

25. EVALUATING THE SIGNIFICANCE • Identify areas in the structure that are likely to be adversely impacted by firebombing usage and assess exactly how they will respond • Structural Analysis/Certification terminology these are termed critical areas, Principal Structural Elements (PSE’s) or Structurally Significant Items (SSI’s) • To do this we need to understand the cyclic stresses experienced at each location • Load is what is applied, stress is how the structure responds • Typically we measure loads • Mechanism of translating these to stresses (Use of “Transfer Functions”) • Detail structural configuration • Evaluate the structural health at each location • Where are we starting from, ie: what has happened in the past • Where are we going, ie: based on the starting point how fast is future usage consuming the “health” of the structure?

26. COMPARISON ASW vs FIREBOMBING • Data from Grumman Tracker (S2) • Canadian Forces ASW • OMNR Firebombing (Undulating) • West Coast Firebombing (Mountainous) • Assuming similar weights and Stress/g of between 5ksi/g and 10ksi/g • Firebombing is approximately 1.8 to 2.0 times as severe as ASW

27. CHALLENGES OF SPECIAL MISSION AIRCRAFT • Generally older aircraft • May or may not be supported by the OEM or a type certificate holder • Frequently not supportive or consider it not cost-effective to generate data for this role • Liability/Risk issues • Engineering data is often limited • Regular data collection and validation is not easy as aircraft are frequently geographically dispersed • Frequently not equipped with a data-bus that facilitates the straightforward capture of many parameters

28. HOW DO YOU GO ABOUT EVALUATING THE ONGOING STRUCTURAL HEALTH OF AN AIRCRAFT? What do you measure, what criteria do you use?

29. ACTIONS INITIATED • USDA/FS & Sandia Laboratory inspection base-lining program • Development of Structural Health Management Plans by some operators • Including generic and specific parameters • Instrumentation of a C-130A Aircraft and development of initial firebombing profiles • Sponsored by the FAA and TBM/IAR • Initial instrumentation and limited preliminary analysis of North American Based Airtankers • Sponsored by the USDA/FS and Sandia Laboratories • 2003 – P2, P3, DC-7 and possibly CV-580 • 2004 – Additional aircraft

30. BASELINE INSPECTION PROGRAM

31. PURPOSE • Reduce risk of major structural failure • One time for 2003 season • Enhanced Inspection Program • Determine the condition of the fleet • Basis for continuing program for long-term airworthiness • Standardization among contractors and types • Identify best practices

32. PROCESS • Documentation search • Historical information • OEM and other user documents • Site visits to all large air tanker contractors • Inspection documentation • Inspection practice • Damage histories

33. SANDIA FINDINGS • Damage Tolerance Assessment • P-3 • US Navy missions most relevant to P-3C • Full scale fatigue testing (P-3C, 2002-2003) • P-2V • No relevant data identified • C-54-DC, DC-6, DC-7 • SID on DC-6 only • 1992 • Based on service history

34. SANDIA FINDINGS (cont) • Inspection Programs (AIPs) • Wide variation in depth and detail of AIPs • No FAA process for standardization or periodic review • Wide variation in use of NDI beyond visual inspection

35. SANDIA FINDINGS (cont) • Existing history data and inspection practice are less effective than true damage tolerance assessment as air tanker time builds in relation to prior mission time • Flight environment and loads data are essential elements of a damage tolerance based continuing airworthiness program, for both current and future air tankers

36. IMPLEMENTING A STRUCTURAL HEALTH MONITORING PROGRAM

37. Previous Flight or Full-Scale Tests Past Service History Maintenance Records as a Firebomber Aircraft Configuration and Model Variants Critical Area Geometry Factors Relevant Materials Data Loads Actually Experienced by the Aircraft in Critical Areas Operational Data Acquisition and Validation Development of New Techniques Parameters to be Monitored Recorders and Instrumentation Data Analysis and Dissemination Field Deployable Depot Level Structural Health Management Plan Considerations Critical Area Identification Certified, Safe and Economically Viable Aircraft Fatigue and Damage Tolerance Analysis Inspection, Maintenance and Overhaul Intervals

38. PROGRAM SCOPE • Limited Survey and assume representative of fleet usage • Loads Environment Stress Survey (LESS) • Most severe Safety Factors • Finite Commitment • Repeat periodically to assess validity • LESS plus limited Individual Aircraft Tracking (IAT) program • Representative IAT aircraft to confirm LESS data remains valid • Safety Factors not as severe • Ongoing commitment • Repeat LESS when significant change in usage occurs • LESS program plus full IAT program • Generally subset of LESS parameters on IAT aircraft • Least severe safety factors • Ongoing commitment • Repeat LESS when significant change in usage occurs Initially Required for Firebombing as “representative” usage may not exist

39. Principle # 1: Minimize parameters to be monitored Even though cost of additional channels and sensors relatively cheap Avoid “If we are not sure let’s monitor it syndrome” AKA “More data has to be better” SELECTING PARAMETERS

40. IDENTIFYING PARAMETERS • Requirements • New requirements • Service History • Testing • Use of Existing or Development of Transfer Functions • Stress Analysis, Test Data, etc. • Durability/Reliability in Operational Environment • If you cannot reliably measure it or if robust sensor cannot be installed, the parameter is of little use • Integration with aircraft systems • Avoid impact on critical systems or structure • Do not want airworthiness or certification issues • EMI/EMC has to be considered • Components themselves • Installed in aircraft

41. GENERIC vs SPECIFIC PARAMETERS • Generic parameters are “universal” parameters that characterize the phenomena being measured • Vertical Centre-of-Gravity Acceleration (Nzcg) • Specific parameters are parameters which represent the actual response of the structure to the phenomena • Strain gauge readings measured at specific locations on a structure • Location specific • Ideally, require as many generic parameters as practicable • Practice: Require a combination of both

42. SIGNIFICANT PHASES OF FLIGHT? TAXI/TAKE-OFF “HEAVY” “BOMBING RUN” “LIGHT” LANDING

43. DATA CAPTURE REQUIREMENTS

44. HOW/WHERE WILL IT BE OBTAINED? • For each parameter you need to know • Measured • Direct reading? • Computed on Aircraft or Post-Flight? • Constant Recording or Discrete Signal • What triggers/toggles recording on/off?, eg: • Application of Aircraft Power • Weight-on-Wheels • Airspeed below a certain value for a certain time • Derived from data on Aircraft Bus • Computed on Aircraft or Post-Flight? • Derived from Ground (Meta) Data • Interrogation of hard-copy data from form? • Interrogation of electronically stored data? • Will data be obtained from a central location or from geographically dispersed locations?

45. Continuous Airspeed Centre-of-Gravity Acceleration (Nzcg) Roll acceleration Pressure Altitude Radar Altitude Flap Position Aileron Position Elevator Position Float Position ( Continuous Flow) Discrete Weight-on-wheels Firebomb door sequencing (weight) Supplementary Data Fuel Load (Average Fuel Burn rate) Flying Hours Configuration Expansion 4-8 channels to address type related issues if required Probably with strain gauges POTENTIAL PARAMETERS

47. SOURCES OF DATA ERROR • Hardware • Faulty Recorders and or Sensors • Sensor installation problems • Incorrect recorder initialization procedures • Software • Incorrect data downloading and/or transcription • Incorrect configuration tracking • Universal implementation of fleet-wide modifications • Inappropriate application of Fill-in data

48. TYPES OF DATA ACQUISITION ERROR • Two general classifications • Logical Errors - Errors that can easily be identified as right or wrong • Range checks • Event response frequency • Potential Errors - Errors which only become apparent over time and/or require detailed analysis by skilled personnel • Strain gauge drift

49. FINAL DATA VALIDATION • Confirming initial (logical error) checks performed at operational bases • Evaluating potential error checks • Strain gauge drift • Over time, implicit need for historical data • Have to compare like data, implicit need to track data by configuration • Tracking initialization readings a good first start • Statistical Validation • Beware of self-fulfilling prophecy • Look for change in usage • Value of Exceedance curves and other tools

50. OPERATIONAL ENVIRONMENT • Primary requirement is to provide a minimal increase in operational workload • You will not get the data you require if: • Acquisition equipment requires: • Too much hand holding • Takes too much time to download • Is not straightforward to use • Cannot easily be maintained or supported • Benefits of collecting data you do not require!!!