A Programmatic Approach to On Condition Maintenance

1
A Programmatic Approach to On Condition
Maintenance

• Chad Wogoman
• NAVAIR
• T58 FST

Frank Eason NAVAIR H46FST
2
Background Where we started

• Purchased 80 COTS Honeywell Model 8500C
  Balancer/Analyzer, as existing equipment was not
  supportable (1.56 M, FY 96)
• Engine Front Frame Cracking 1 Safety Issue
• Vibration due to poor RTB causing cracking
• Excessive 1 Bearing oil leakage, ingested by
  engine, caused in-flight emergency engine shut
  downs
• Costs squadron man-hours and engine replacement
• Premature structural and hinge point failures
  experienced
• New RTB procedure successfully developed to
  eliminate engine front frame cracking
• DCC-81 Modified rotor blades (105K, FY 97)
• Elimination of Whirl Tower saved 5M Annually

Drive to utilize equipment to its capacity
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Phase IGetting Started and Setting the
Foundation
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Initial Testing and Instrumentation

• COTS equipment could collect vibration data
• COTS software needed to automate the O level
  aspect of the analysis
• Develop the frequency models of the engine and
  drive train
• Optimize sensor locations through surveys and
  initial testing
• Collect data that can help establish good
  vibration limits
• Validate the system approach before fleet
  implementation

Learn the Aircraft
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Data Analysis Software

• Merely collecting data without having tools to
  drive real world interpretation will lead to
  failure
• Limits and data collection sequences must be
  modifiable by the Navy Engineering Staff
• Older Vibration Equipment required the vendor to
  modify software any time a change was needed
• Software should keep it simple for the end user
• Maintenance manuals should interface with
  analysis system

Analysis Software is Key
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System Training

• Teach the theory, not just the how
• Instructional and practical/hands-on methods
  required
• Share results
• Empower the user to be a part of the system
  developments/enhancements
• Technical representatives at the sites are key to
  success

Communicate system benefits through training
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Phase IIPeriodic Vibration Checks
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Slow methodical implementation

• 100 hour/phase checks increased knowledge
• Gained momentum as troubleshooting tool
• Maintenance time decreased
• Data review identified issues we never could have
  seen with previous test methods
• Allowed us to evaluate effectiveness before
  spending a lot of money
• Avoids false removals / A799 rates
• Able to grant high time component life extensions
• Fleet demand drove follow-on buy of 30 more 8500C
  units (780K, FY 98)

Early steps realized significant savings
9
Five Significant Case Examples

• High Speed Shaft Resonance
• High Speed Shaft Adapter Imbalance
• Main Electrical Generator failures
• Service life extensions for aft transmissions
• Excessive engine vibrations

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High Speed Shaft Resonance

• Problem
• Damaged torque sensors
• Erroneous torque readings
• Findings
• Spline wear allowing resonance in HSS
• HSS resonance undetected with previous equipment
• Pilots troubleshooting by throttling the engine
  back and causing resonance
• Spectral analysis equipment can detect resonance
• Resolution
• Inspection of spline wear implemented
• Check for resonance with use of narrowband
  equipment when erratic torque readings reported
• Pilots instructed to operate at 100 Nf/Nr

Damaged Torque Sensors
Emergency Shutdown level _at_ 20 gs Old Equipment
did not detect
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High Speed Shaft Adapter Imbalance
Improperly Balanced Adapter

• Problem
• Increase in shaft removal rejection
• Seals failing
• Engines and transmissions were being removed
• Findings
• Periodic vibration checks expanded to in flight
  regimes revealed HSS levels as high as 26 gs
• Balancing procedures at vendor and depot
  facilities found to be inadequate
• Resolution
• Balance machines updated and match set balancing
  implemented

120 KIAS regime recorded vibe levels above
shutdown limit (20gs)
Hover limit 3.6 gs
Ground limit 5 gs
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Electrical Generator Failures

• Problem
• Catastrophic generator failures
• Failures causing in-flight hazards emergency
  shutdown
• Findings
• Change in scheduled maintenance allowing
  generators to run to failure
• Resolution
• New vibration check procedure identifies degraded
  generators before catastrophic failure
• Scheduled overhaul replaced with vibration check
  (on-condition)
• Saves 900K per year

Rotor Contacted Stator
Bearing Housing Damage
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AFT Transmission Life Extensions

• Problem
• High time of Aft Xmsn is 900 hours
• Life extensions granted without data
• Untimely failures resulted
• Findings
• Failures can be detected by vibration analysis
• Resolution
• Mandatory submittal of vibration data required
  for life extensions
• If able to eliminate resonance the Xmsn may be
  able to extend to 1800 hours

Collector/spur gear mesh
Sideband spacing at spur Gear 1 per speed.
Multiple sidebands
1X of Spur gear
Multiple Harmonics of Spur Gear
3X
5X
2X
4X
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Excessive Engine Vibrations

• Problem
• Loud audible howl on newly overhauled engine
• Findings
• All test cell runs passed
• Mils Broadband was acceptance criteria
• Mobile test cell failed to identify problem
• Poorly balanced compressor rotor caused damage to
  8th, 9th, and 10th stages of the rotor
• Resolution
• 3 spectral analyzer fielded in test cells for
  data collection

Compressor Rotor Speed at 81 Ng
Note Fleet average for this frequency is below
.2 IPS
Test cell run using spectral analysis vs
Broadband Note Limit was 1.5 Mils.
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Phase IIIJustification for Hardwiring of
Aircraft
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Eng Drive Shaft Catastrophic Failure

• Problem
• Test of 1 2 Engine Drive Shafts indicated
  misalignment on Engine 1
• Findings
• Maintenance performed and aircraft released to
  serviceability
• 2 Engine Drive shaft failed catastrophically in
  flight
• Equipment installed incorrectly
• Maintenance performed on incorrect shaft
• Resolution
• Human error allowed component to fly to failure
• Hardwiring would have prevented this error

Above Limits
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AFC 433 Part 12

• Purchased kits to install sensors and wiring in
  approximately 180 aircraft (1.2M, FY 00)
• Prepares aircraft for onboard vibration system
  expansion
• Solved fleet driven complaints about SE wear and
  tear

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Phase IVTest Cell Expansion
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Initial Testing and Implementation

• Began initial data collection using 3 8500C
  spectrum analyzers in late 1999
• 2 at NADEP Cherry Point
• 1 at MALS-29/26
• Noted significant gains by progressing towards
  spectral analysis
• Provided means to isolate specific frequency(s)
  yielding greatest amount of vibration
• Significant unbalance conditions noted on main
  rotating components
• New balance machines and procedures incorporated
  (350K)
• COTS spectrum analyzers (VXP) fielded in early
  2001 (235K, FY 01)
• Spectral analysis now used on all test cells to
  accept/reject engines

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Older Vibration System Costs

• Vibration data collected by Broadband system had
  falsely led fleet to reject multiple Power
  Turbine assemblies due to excessive vibration
• GE proposed an expensive redesign of the PT
  bearing/housing as a viable solution
• COTS vibration analyzers uncovered the dominant
  frequency causing the vibration, which was the
  Gas Generator Turbine
• Immediately avoided countless PT overhauls (fleet
  wide)
• GE ceased bearing redesign effort
• Yearly savings realized, using spectral analysis,
  due to fault isolation capabilities
• PT Rotor Cost 47,757/unit
• PT Assembly Cost 99,264/assembly

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Substantial Finding Impending Bearing Failure

• Problem
• Engine passed test cell based upon Broadband
  vibration test
• Rejected on-wing due to audible howling
• Findings
• Spectral analysis indicated Gas Generator Turbine
  as the problem area
• Troubleshooting with the spectral analysis
  concluded to non-synchronous behavior, indicating
  spinning bearing race
• Large fragments found upon teardown
• Test cell Broadband equipment not properly
  configured
• Resolution
• Early detection of bearing wear possible with
  spectral analysis, avoiding potential
  catastrophic failure on-wing

Vibration pattern changed un-proportional with
engine speed
Note concave contour of journal surface (OD was
.052 in undersized as a result of spinning inner
race)
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Return on Investment
TAT

• Spectral analyzer implementations yield
  significant benefits
• Increased engine avg. mean time since repair
• Decreased engine turn around time
• Increased average net spares available

Net Spares
MTSR
Operation Iraqi Freedom
Operation Iraqi Freedom
Beginning of Vibration Program
Beginning of Vibration Program
Implemented VXP System
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Phase VOn-Board Systems Increase Safety
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Aft Transmission Bearing Failure

• Problem
• Aft Transmission Smoking in flight
• Findings
• Bearing Failure
• Gearbox failed after bearing failure resulting in
  sheared lube pump shaft
• Loss of pump caused over temp in flight
• Resolution
• 100 Phase check was not performed
• Automated on-board system would have prevented
  this human induced error

?
NO VIBE DATA TAKEN!
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Head Bearing Failure

• Problem
• Post Phase vibration checked and passed
• Significant increases in vibration reported by
  the crew after only a few hours of flight
• Findings
• Repeated vibration checks verified the crew
  discrepancy
• Vib levels had risen over a short period of time
• Sr. Squadron officer instructed the aircraft to
  remain in service
• 7 hours later the flight was aborted by the Air
  Boss aircraft significantly shaking on deck
• Failed head seal and bearing found
• Oil leakage problem was ignored
• Lack of lubrication led to failure
• Rotor head hub was close to total failure that
  would have resulted in a complete loss of the
  aircraft crew
• Resolution
• On-board equipment would have indicated the
  problem immediately

Figure 22 Here

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Phase IVOn Board System Aircraft Integrated
Maintenance System
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Eliminate Support Equipment

• Honeywell Rotor Track and Balance Model 8500C
• Vibration Signature Carry On Accessory Kit
• Howell Instruments Engine Check System NP600
• Purchased NRE and AIMS units (16M, FY 03 08)

Logistics Savings Realized
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Key Features Derive Solutions

• Rotor Track Balance
• Periodic Vibration Checks
• Continual Vibration Monitoring
• Engine Performance Checks with automatic
  nomograph and margin calculations
• Continual Aircraft Engine Parameter Monitoring
• 1553 Databus interface
• Interface to Control Display Navigational Unit
  (CDNU) via the 1553 databus
• On Board Go/No Go indications with simple user
  interface for the aircrew
• Ground Station Software with Go/No Go
  indications, data archival, data review analysis

Features with immediate payback
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RTB Displays

• Polar Plot Display
• Track Display
• Measurements Solution Display
• Adjustments

Improves Troubleshooting Capability
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Periodic Checks Continual Monitoring

• User definable configurations via Engineering
  Ground Station Software
• Multiple alarming levels, which drive visibility
  to aircrew
• Master Caution Panel
• On CDNU Display
• On AIMS Acquisition Unit
• On Ground Station

Immediate Feedback of Alarm Conditions
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Periodic Checks Continual Monitoring

• Monitors
• Engine and Drivetrain Vibration Levels
• Overspeeds
• Overtorques
• Overtemperatures
• Chip and Debris Screen States
• Oil Temperature and Pressure
• Engine Performance Margin
• Air Data (OAT, PA, KIAS via 1553B data bus
  interface)

Increasing Safety Reliability
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Engine Check Displays

• Engine performance assessed on-board, resulting
  in immediate feedback of acceptability
• Complete post maintenance check flight engine
  setup capability

• Migrating towards fully automated performance
  margin on the fly
• Potentially eliminating phase performance check
  requirement
• Potentially aiding mission planning efforts

Eliminate Manual Data Entry and Plotting of Data
Points
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AIMS Savings Realized

• Annual FCF hours using AIMS will be reduced by
  1117 hrs resulting in a savings of 10,938,505
  based on FY04 data
• FCF setup time In addition, the time savings
  will easily surpass 8,000 man hours annually
  required to set up for FCFs
• SE savings calibration, repair, fleet readiness
• AIMS monitor feature has potential to uncover
  component anomalies, prior to catastrophic
  failure, inherently save parts and will increase
  safety

Features with immediate payback
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Conclusion
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System Selection Critical

• Automation is good to a point
• No COTS system is 100 ready to go
• Demand control of configurations (routes
  limits)
• Control getting drowned in mass amounts of data
• The system must cater to the operator and
  maintainer
• More is not necessarily better
• Must be simple at end user
• Must inform the operator/maintainer of pending
  problems or failures
• Grow the system as lessons are learned
• Off site analysis is not practical
• Must conform to new software requirements - NMCI

Understand how your system works for you
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Making room for growth

• Advanced Gearbox Diagnostics
• Monitoring of flight controls
• Flight regime recognition for engine performance
  calculations
• Automation of data management, diagnostics and
  prognostics
• RTB SmartChart Technology Tell the
  maintainer what is wrong with the aircraft

Develop smart solutions
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Benefits are tangible

• Significant Cost Savings
• Achieved highest readiness rating
• Engine availability improved
• Back shop procedures improved
• Safety of flight improved

We have realized a significant return
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Questions?
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Backup slides
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Tool to reduce Total Cost of Ownership

• Man-hour/Cost Savings/Readiness Improvement
• Replaces unreliable/unavailable Support Equipment
• Reduces troubleshooting time dramatically
• Eliminates unnecessary removal of good dynamic
  components
• due to shotgun troubleshooting approach
• Operational Improvements
• Provides in-flight warnings of impending
  catastrophic failures
• Provides vib/engine data for fleet/FST
  diagnostics
• Other benefits
• 100 compatible with existing 8500C data
• Easy data sharing between O, I, D and FST

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Savings Through Diagnostics

• Fault-based maintenance is an expensive practice
• Reduces availability
• Drives unscheduled maintenance
• May involve collateral damage or flight mishap
• Condition Based Maintenance (CBM) is possible if
  you can first assess condition
• Reduced OS costs
• Increased safety, reliability and availability
• More efficient use of personnel through
  application of technology

Diagnostic Systems like AIMS is a key enabler of
CBM
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CH-46E CURRENT OPERATING SUPPORT COST
9,140 Cost per Flight Hour OS is driven by both
Direct Maintenance Cost and other indirect costs.
O S
5,100 Cost per Flight Hour DMC is driven by
depot repair and overhaul of dynamic components
and transmissions
DMC
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Cost Benefit Analysis (CBA) Technical
Maintenance Summary
CBA Cost Factor Reduction ()
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AIMS TOTAL COST AVOIDANCE FY05
13.7 M
10.1 M
3.6 M
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BREAK EVEN POINT Based on POM 06 TAI
Current
Cost Avoidance
154 Installations Completed 4TH Qtr FY 07
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BREAK EVEN POINT Based on POM 06 TAI
Current
Actual Cost Avoidance (Installs)
Cost Avoidance
154 Installations Completed 4TH Qtr FY 07
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Quantifying AIMS Savings

• Based on 154 AIMS aircraft and percentages from
  FY04
• 3920 Functional check flights.
• 3724 Flight hours to perform FCFs
• 9791 Cost per flight hour (FY04 cost data)
• Total cost for FCFs in FY 04 equals 36,461,684
•  
• Input from Val/Ver flight crews. First FCF
  performed with AIMS was a complete card on both
  engines. Total time with an unfamiliar crew was
  under an hour. As the crew becomes familiar with
  the system, times continue to reduce. A very
  conservative estimate is a 30 reduction in
  flight times for FCFs with AIMs vice using the
  NP600 for engine set-ups. After entire fleet has
  been converted to AIMS total flight hours would
  be reduced by 1117 hrs at a 10,938,505 savings
  based on FY04 data.
• Rotor Track and Balance timesavings have been
  significant as well. Due to the speed at which
  the AIMS system calculates solutions and the need
  for SE being removed, the engineering staff
  estimates at least a 50 reduction in the amount
  of time it takes to get an aircraft ready to go.
• Possibly the biggest value to the AIMS system is
  the removal of the NP600 for engine set up and
  the 8500C for RTB. A typical set up for either
  of these pieces of gear takes 2 marines around an
  hour to prep for flight when all the gear is
  available and RFI. More often than not, the gear
  is down or in for cal etc. and the time it takes
  to get the equipment and be ready for flight can
  take upwards of 3-4 hours. I created a
  spaghetti diagram based on a typical scenario
  for the current method of FCFs and one after
  AIMS is installed. Installation of AIMS will cut
  the need for mechs to walk to the SSE room, Cal
  shop etc. to get the gear. I estimate a typical
  walking savings of 5400 feet per FCF for a total
  of over 4000 miles per year that the mechs dont
  have to walk to set up for FCFs. In addition,
  the time savings will easily surpass 8,000 man
  hours required to set up for FCFs.