rcm eaa
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EAA Chapter 393 (June 2008)
Copyright 2008 Savvy Aviator, Inc.
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Chapter 393Reliability-CenteredMaintenance (RCM)
The science of achieving
better safety & dispatch reliability
by doing less maintenance!
EAA Chapter 393 (June 2008) Copyright 2008 Savvy Aviator, Inc. 2
Chapter 393Who uses RCM?
Airlines (1970s-)
Air Transport Ass’n MSG-3
Military aviation (1980s-)
Non-aviation (industrial)Nuclear power plants
Oil refineriesWater treatment plantsMarine vessels
Heavy equipment manufacturing
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Chapter 393
Benefits of using RCM
0
50
100
150
200
250
300
350
Components subject to scheduled overhaul
or replacement
DC-8: 339
DC-10: 7
DCDC--8:8:TraditionalTraditional
DCDC--10:10:RCMRCM
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Chapter 393Benefits of using RCM
0
500000
1000000
1500000
2000000
2500000
3000000
3500000
4000000
Man-hours of structural inspections
(first 20,000 hours TIS)
DC-8: 4,000,000
B-747: 66,000
DCDC--8:8:TraditionalTraditional
BB--747:747:RCMRCM
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Chapter 393
Benefits of using RCM
RCM has saved the airlines a fortune by
Slashing the amount of scheduled PM
Eliminating most TBOs
Big surprise: When PM was slashed andTBOs eliminated, aircraft safety and dispatchreliability improved dramatically!
Q:Q: How can doing LESS maintenance result in
MORE safety and reliability? A:A: By reducing MIFs (Maintenance-induced failures)
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Chapter 393
Maintenance is inherently invasive —it oftenbreaks things that were previously working fine
We call this a maintenance-induced failure (MIF)
The more invasive the task, the more likely a MIF
Performing unnecessary maintenance
Wastes money and increases the risk of MIF
Eliminating unnecessary maintenance
Saves money and improves safety and reliability
Maintenance has a dark side!Maintenance has a dark side!Maintenance has a dark side!
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Chapter 393
Traditional vs. RCM
Traditional view:
Maintenance is a good thing
The more we do, the better
RCM view:
Maintenance is a necessary evil…like surgery
The less we do, the better
We should do it only when absolutelynecessary, or when the benefits clearlyoutweigh the associated risks and costs
EAA Chapter 393 (June 2008) Copyright 2008 Savvy Aviator, Inc. 8
Chapter 393Key RCM questions
What are this component’s failure modes?
For each failure mode:
How likely is this failure to occur?
Is the probability of this failure:
Higher when component is old? (“age-related”)
Higher when component is young? (“infant mortality”)
Unrelated to component age? (“random”)
How serious are the consequences of this failure?
Can we detect an incipient failure before it occurs?
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Chapter 393
TDM versus CDM
Time-directed maintenance (TDM)
Attempts to avoid failures by retiring, replacing oroverhauling components at a specific age (TBO)
Condition-directed maintenance (CDM)
Attempts to avoid failures by monitoring componentcondition to detect potential failures before theybecome functional failures
CDM is always more efficient than TDM TDM should be used only when CDM is infeasible
EAA Chapter 393 (June 2008) Copyright 2008 Savvy Aviator, Inc. 10
Chapter 393Hierarchy of consequences
Safety consequences Failure might hurt or kill someone Example: engine connecting rod failure
Hidden consequences Failure invisible to crew, and might reduce safety Example: failure of standby vacuum system
Operational consequences Failure might make aircraft unflyable (AOG) Example: failure of a magneto
Economic consequences Failure has no significant operational impact Example: failure of #2 comm radio
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Chapter 393
RCM decision tree
Risks damage?
Impacts mission?
Impacts safety?
Is CDM effective?
Is TDM effective?
Perform CDM Perform TDM
Accept failure,redesign system,
or add redundancyRun to
failure
Yes
No
Yes
Yes
Yes
Yes
No
No
No
No
EAA Chapter 393 (June 2008) Copyright 2008 Savvy Aviator, Inc. 12
Chapter 393Age-related failures
Traditional view…
A few premature failures Unacceptable rate of failure
TBO TBO Safe Life Safe Life
Do our pistonDo our piston
aircraft enginesaircraft engines
exhibit thisexhibit this
failure pattern?failure pattern?
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Chapter 393
Engine-failure accidents (2001-2005 small piston airplanes)
Age-related failures
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Chapter 393
Engine-failure accidents (2001-2005 small piston airplanes)
????
!! !!
Past TBO?Past TBO?
InfantInfant--mortality!mortality!
Age-related failures
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Chapter 393
Age-related failures
Second-generation view…
OVERHAUL AT TBO??? OVERHAUL AT TBO???
“ “ Bathtub curve Bathtub curve ” ”
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Chapter 393Age-related failures
Third-generation view (RCM)…Age-relatedNon-age-related
77% to 92% 8% to 23%
TBO makes sense for TBO makes sense for only 4% to 6% of theonly 4% to 6% of the
components on civil A/Ccomponents on civil A/C
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Chapter 393 Simple items
One dominant failure mode (e.g., metal fatigue)
Failure probability often increases with age
An age limit, safe-life limit, or TBO may be useful
Complex items
Many different failure modes
Failure probability usually doesn’t increase with age Age limits, safe-life limits and TBOs are not effective
Simple vs. complex
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Chapter 393Condition monitoring
Rule of thumb:
For condition monitoring to detect potential failures reliably and
prevent functional failures, we must inspect for potential failures
at approximately one-half of the P-F interval.
Scheduled inspection for potential failures (P)
intended to prevent functional failures (F)
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Chapter 393
Nowlan & Heap report: “Reliability Centered Maintenance”Dec. 1978, 520 pages
http://www.savvyaviator.com/rcm_nowlan_heap.pdf
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Chapter 393Let’s talk about TBO…
Overhauling an apparently healthy engine at
TBO makes very little sense
Complex item, no single dominant failure mode
so overhauling at TBO is not an effective methodof reducing failure risk
Most likely catastrophic failure is infant mortality
so overhauling arbitrarily at TBO is more likely toincrease risk than decrease it
Why throw away years of useful life?
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Chapter 393
Let’s talk about TBO…
Operating an engine beyond TBO…
…is absolutely legal
…won’t void your aircraft insurance
…won’t make the overhaul more costly
…won’t make a catastrophic failure more likely
In fact, it will do exactly the opposite!
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Chapter 393A tale of two engines
My 1979 Cessna T310R has two TSIO-520-BBs
TCM’s published TBO is 1,400 hours
On first run, these engines ran trouble-free for
1,900 hours SNEW, then field overhauled
Why? Because I chickened out! (Pretty dumb, huh?)
At teardown, engines immaculate
All 12 cylinders re-valved and continued in service At TBO (1,400 SMOH), running great
At 2,300+ SMOH (164% of TBO), still running fine
This time, I’m in no hurry to overhaul!
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Chapter 393
TBO do’s and don’ts
How we should use TBO
Use it to plan reserve for overhaul
Use it to adjust fair market value
How we should not use TBO
Don’t euthanize an engine just because it hasattained some arbitrary age
Why throw away years of useful life?
Monitor engine health using all available tools, andoverhaul strictly “on condition”
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Chapter 393Compression test
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Chapter 393
Compression test
Mandated by FARs but problematic:
Very unrealistic test conditions
Poor precision and reproducibility
Sensitive to equipment, technique
Numerous “false positives”—tens of thousandsof cylinders have been removed unnecessarilydue to “weak compression”
Never pull a jug solely because of a low compression reading!
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Chapter 393Compression test
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Chapter 393
Oil filter inspection
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Chapter 393Oil filter inspection
Mandated by FARs
Very important test, but has limitations:
Won’t detect microscopic wear metal particles<20 microns
May not detect large chunks >1/16”
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Chapter 393
Oil filter inspection
But may not detect this…Will detect this…
EAA Chapter 393 (June 2008) Copyright 2008 Savvy Aviator, Inc. 30
Chapter 393Oil filter never saw this!
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Chapter 393
Oil filter inspection
How much metal is too much?
TCM does not offer guidance
Lycoming says ground the aircraft if
filter is found to contain:
Any large pieces of metal(the size of broken pencil point)
Numerous small particles totaling¼ teaspoon or more
Anything less, fly and re-evaluate
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Chapter 393
¼”¼”
≈≈
¼¼ teaspoon of ferrous metalteaspoon of ferrous metal
On the tip
of amechanic’s
magnetic
pickup tool
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Chapter 393
Dry particle analysis
When significant metal is found in filter :
Use magnet to identify if ferrous or non-ferrous
Send filter contents to labfor scanning electron microscopy (SEM)
Can often identify the exact source of the metal
TCM and Lycoming both do this
Also independent labsAviation Laboratories, http://www.avlab.com/
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Chapter 393Oil pressure
Transient in-flight oil pressure fluctuation
may indicate chunks of metal (or other foreignmaterial) passing thru pressure relief valve
Land immediately!
Check oil filter, pickup screen, governor gasket
In technically-advanced aircraft, might be anelectrical gremlin—but you must assume
it’s real unless proven otherwise
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Chapter 393Spectrographic oil analysis
Complements filter inspection
Detects microscopic wear metal particlesthat are too small to see
Establishes a baseline “wear signature” forengine, then looks for departures from thatnorm
Oil analysis excels at:
Detecting very slow wear events
Early warning of accelerating wear
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Chapter 393Spectrographic oil analysis
272949225132454/30
12273431891972/992744520815011/15
10284481991038/27
8394622212555/5
851361152823102/1
SiSnCuNiFeCr Al
----- Parts Per Million -----Total
Hours
Sample
Date
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Chapter 393
Borescope inspection
90-degreeviewing angle
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Chapter 393Borescope inspection
Internal cylinder inspection
Without cylinder removal
Now “required” by TCM SB03-3
at each compression test and
annual/100-hour inspection
FAA says it’s not compulsory for Part
91…but you’d be crazy not to!
Eliminates most “false positives” ofcompression tests
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Chapter 393
Borescope inspection
Best cylinder
borescopeI’ve
found so far is a
dental intraoral
camera!
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Chapter 393Borescope inspection
ExhaustExhaust
ValveValveIntakeIntake
ValveValve
Thisexhaust
valvelooks
normal
Notesymmetrical
exhaustdeposits
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Chapter 393
Borescope inspection
Thisexhaust
valvelooks fine
Notereasonablysymmetrical
depositpattern
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Chapter 393Borescope inspection
Thisexhaustvalve is
burned!!!
Noteasymmetrical
deposits, andarea devoidof deposits(“hot spot”)
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Chapter 393
#3 Exhaust Valve#3 Exhaust Valve
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Chapter 393
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Chapter 393
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Chapter 393
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Chapter 393
EAA Chapter 393 (June 2008) Copyright 2008 Savvy Aviator, Inc. 48
Chapter 393Digital engine monitors
JPI EDM-760 Insight Gemini 1200
JPI EDM-700 E.I. UBG-16 Insight GEM-610
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Chapter 393
JPI EDM-930 E.I. MVP-50
XerionAuRACLE
Digital engine monitors
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Chapter 393Digital engine monitors
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Chapter 393
Absolutely indispensable for real-time
monitoring and diagnosis of:
Burned exhaust valves
Misfiring spark plugs
Faulty ignition leads
Improper magneto timing
Clogged fuel injectors
Induction leaks
Cooling baffle problems
Digital engine monitors
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Chapter 393EGT
CHT
4 Hours
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Chapter 393EGT
CHT
4 Hours
What’s wrong with this engine?
~30°F
20 cycles in 30 minutes
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Chapter 393
#3 Exhaust Valve#3 Exhaust Valve
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Chapter 393
Burned exhaust valve
Signature is “dancing EGT”
EGT variation ~30-50°F, often ~1± cycle/minute
If your analyzer isn’t in “normalize” mode,you’ll never notice it!
Distinguishing from a failing probe
or loose connection
Usually rapid and random,
not slow and rhythmic Usually spikes DOWN (not UP)
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Chapter 393Apr 9, 2005Apr 9, 2005
Jun 5, 2005Jun 5, 2005
Jul 28, 2005Jul 28, 2005
Aug 7, 2005Aug 7, 2005
Aug 21, 2005Aug 21, 2005
#2 EGT#2 EGT
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Chapter 393
TCM IO-520
One Minute
ROP→ LOP
“Big Mixture Pull”Rough Engine
#2 & #4 go cold
Enrich a bit
#2 & #4 come back
but EGT erratic
EGT
CHT
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Chapter 393
ROP→ LOP
“Big Mixture Pull”#5 EGT and TIT
drift up; other
EGTs stable
TCM
TSIO-52010 Minutes
EGT
CHT
Pilot goes full-rich,
then leans a bit
less aggressively
#5 EGT and TIT
are now stable
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Chapter 393
Is it fuel or spark?
Fuel-related problems usually cause CHTand EGT to move in the same direction
Ignition-related problems usually causeCHT and EGT to move in the opposite
direction
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Chapter 393
TCM
TSIO-520
EGT
CHT
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Chapter 393
TCMTSIO-520
EGT
CHT
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Chapter 393Troubleshooting high CHT
Two possibilities:
Too lean
Poor cooling
If cylinder is running too lean: Hot when ROP
Cool when LOP
If cylinder has inadequate cooling air (dueto problems with baffles and/or baffle seals): Hot when ROP
Hot when LOP
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Chapter 393
Using these tools together
Never remove a cylinder or tear down an
engine based on any one test:
If there’s a real problem, it will almost alwaysreveal itself in several ways
If the preponderance of the evidence allpoints in the same direction, you can beconfident of the diagnosis
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Chapter 393Using these tools together
Example:
Feb. 2006, oil analysis shows elevated nickel.
Apr. 2006, RE #3 compression is “funky”but exhaust valve looks fine under borescope.
Mar. 2007 (11 months and 150 hours later),engine monitor shows RE #3 EGT jitters.
Borescope clearly shows two hot spots on valve.Compression test shows RE #3 at 0/80.
Verdict: Replace RE #3 exhaust valve & guide
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Chapter 393
A 21st century engine condition
monitor ing program includes:
Oil filter inspection
SEM analysis of filter contents
Spectrographic oil analysis
Oil temperature & pressure trend analysis
Compression test
Borescope inspection
Spark plug inspection Digital engine monitor data analysis
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Chapter 393
Secrets of Cost-Effective
Maintenance
Five simple rules that can
dramatically reduce your
maintenance expenditures,year after year
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Chapter 393
Maintenance is a team sport!
FAAFAA Certificated mechanic (A&P)
Performs repairs and alterations
Analogy: “licensed electrician, plumber, roofer”
Authorized inspector (IA)
Inspects and approves (annuals, 337s)
Analogy: “licensed building inspector”
Aircraft owner/operator
Primary responsibility for maintenance
Analogy: “general contractor”
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Chapter 393Why this teamwork breaks down
Asymmetric knowledge
Owner is theoretically in charge
A&Ps and IAs are theoretically “hired help”
In GA, owner usually has no maintenancetraining and minimal maintenance knowledge
Conflicts of interest
IA determines what work must be done
A&P income derives from work performed
In GA, IA and A&P are usually the same person!
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Chapter 393
Why this teamwork breaks down
Lack of “informed consent”
Aircraft owners routinely approve maintenancewithout knowing:
What it is going to cost
Why it is being performed
Whether it is really necessary for safety
Whether it is required by regulation
How invasive it is
What the risks are Whether the benefits outweigh the risks and cost
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Chapter 393Why this teamwork breaks down
Defensive maintenance
Explosion in litigation since 1994 (GARA)
18-year limit on manufacturer’s product liability
Prior to GARA, A&Ps worried about two things:
It it safe?
Is it legal? (i.e., does it comply with FAA regulations?)
Since GARA, A&Ps have to worry about a third: How will it look to a jury of citizens (who have no
knowledge about aviation or maintenance) when spun inthe most unfavorable possible light by a skilled plaintiff’sattorney?
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Chapter 393The bottom line:
Most aircraft owners
do a terrible job
of managing their
maintenance!
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Chapter 393
www.savvyaviator.com
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Chapter 393
Training may not be enough!
Managing maintenance properly requires a
major investment in time, effort and study
Some owners can’t do this because they’re too
busy running a business or raising a family.
Some owners feel they bought an airplane to
save them time, not cost them time.
Many owners are not comfortable telling their A&Ps what to do (instead of the other way around)
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Chapter 393
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Chapter 393Rule #1:
Choose the right
service facility
and/or technician
for the job.
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Chapter 393An owner’s job #1
As “general contractor” an owner’s job is to:
Hire skilled tradesman (IAs, A&Ps, other technicians)
Manage them to ensure they perform as desired andget the job done within schedule and budget
Fire them if they do not perform to expectations
The most important of these is the first!
If you hire the right person for the job, the resttends to work out well most of the time
If you hire the wrong person for the job, the bestmanagement skills in the world may not be enoughto rescue the situation
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Chapter 393
Hiring the right shop
Most owners do it the wrong way:
The shop is at or near the aircraft’s home base
The mechanic or DOM seems friendly
An aircraft-owner friend recommends it
Much more “due diligence” is required
Interview the shop as you would an employee
Look for the three C’s: Competent Communicative Cooperative
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Chapter 393The three C’s
Competent means the shop has extensiveexperience with your make and model
Communicative means the shop is committedto keeping you continually “in the loop”
Cooperative means the DOM is customer-oriented and willing to do things your way
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Chapter 393Rule #2:
Insist on a written
discrepancy list
and cost estimate
before approvingany work or parts.
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Chapter 393Avoiding “sticker shock”
Never approve maintenance until you know
what it’s going to cost
Get it in writing!
Instruct the shop that they are not authorized toexceed their written estimate unless they give you
an amended estimate and obtain your explicitapproval
If you first learn the cost at invoice time, it’s toolate to affect the outcome!
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Chapter 393
What about inspections?
Require a three-phase protocol:
Shop inspects aircraft (for a flat-rate charge) andpresents owner with a written discrepancy list, withspecific repair recommendations and detailed costestimates for parts, labor, and outside work
Owner reviews discrepancy list and estimates,asks questions, seeks second opinions, doeshomework to ensure informed consent
Owner gives shop specific written direction
and authorization to proceed
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Chapter 393Rule #3:
If it ain’t broke,
don’t let them fix it!
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Chapter 393
If it ain’t broke, don’t fix it!
Every service manual contains hundreds of
scheduled preventive maintenance tasks
Such one-size-fits-all recommendations
make no sense!
Is aircraft based in Tampa or Tucson?
Does aircraft fly 30 hours/year, or 300 hours/year?
Is aircraft hangared, or tied down outdoors?
Compliance is usually not required,
and often is a huge waste of money
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Chapter 393Don’t do it “by the book”!
It never makes sense to maintain any
component on a fixed timetable if it isfeasible to monitor condition and determinewhen maintenance is actually required
CDM is always more cost-efficient than TDM
TCM should be used only if CDM is infeasible
Numerous studies show that CDM is feasible forabout 95% of the components on civil aircraft
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Chapter 393Rule #4:
Don’t let them fix it
until you’re sure
what’s wrong with it!
(Complete the diagnosisbefore starting therapy.)
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Chapter 393Troubleshooting failures
Have you ever had this experience?
You put your aircraft in the shop to have a squawk fixed;
You received an invoice for parts and labor;
You discovered that the squawk wasn’t fixed?
If so, you were victim of
a troubleshooting failure!
Incorrect/inadequate troubleshooting is the
#1 cause of wasted maintenance dollars!
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Chapter 393
Troubleshooting failures
A&Ps are often poor troubleshooters
They are trained as therapists, not diagnosticians
Many aircraft problems cannot be reproduced in themaintenance hangar
If a mechanic can’t reproduce a problem, he can’ttroubleshoot it systematically (so he has to guess)
What’s the solution?
Troubleshoot the problem yourself
Consult with an expert on the system in question
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Chapter 393Rule #5:
Don’t let your shop
overkill the problem!
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Chapter 393
Don’t overkill the problem!
When your airplane has a problem and you’vediagnosed it properly, get it fixed but don’t go
overboard!
If you have a cylinder with a burned exhaust valve,repair the valve, don’t replace the jug
If you have one or two weak cylinders, don’t gettalked into doing a top overhaul
No matter how many cylinders are bad, don’t eventhink about overhauling the engine
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Chapter 393Review: The five rules
1. Choose the right shop and/or technician
2. Require a written discrepancy list & estimate
3. If it ain’t broke, don’t let them fix it
4. Don’t fix it until you’re sure what’s wrong
5. Don’t overkill the problem
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Chapter 393Does this stuff really work?
You bet it does!
Lots of good info at
www.savvymx.com www.savvymx.com