AC (advisory circular

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J U.S.Departmentot Transportation

FodomlAvianon Circular

Subject: RECIPROCATING ENGINE POWER- Date: 6/15/98 AC No: 20-105B

LOSS ACCIDENT PREVENTION

AND TREND MONITORING

Initiated by: AFS-340 Change:

1. PURPOSE. This advisory circular (AC) updatesstatistical information and brings to theattention of aircraft owners, operators, manufacturers, and maintenancepersonnel he

circumstancessurrounding engine power-loss accidentswith recommendationson how, throughindividual effort and consideration, those accidentscan be prevented. This AC will also offer

procedureson how to set up a reciprocating engine rend monitoring program to improve both

engine and related system reliability over the recommendedoperating life of the engine.

2. CANCELLATION. AC 20-105A, Engine Power-Loss Accident Prevention, dated

November 20, 1980, is canceled.

3. BACKGROUND. Four and six cylinder reciprocating enginespresently installed in Civil

’

Aviation Regulation (CAR) 3 and Title 14 of the Code of Federal Regulations (14 CFR) part 23

type-certificated aircraft are the engine of choice for small s ingle engine and multi-engine aircraftbecauseof their reliability. The recommended ime between overhaul (TBO) for reciprocating

engines ange between 1500/l 800 hours for high performance six cylinder engines o 2000 hours



AC 20-105B 6/l 5198

4. DISCUSSION OF OPERATIONAL ENGINE FAILURES.

a. Lack Of Pilot Training. Mismanagement f enginecontrol system(s)by the pilot

continues o be the leadingcause f eng ine ailure. Most of these ypesof failures esult from

improper preflight plann ingor improper uel management rocedures.Fue l starvation fuel onboard he aircraft but not supplied o the engine(s),and fuel exhaustion no fuel on board he .aircraft) account or over 5 1%of all enginepower-lossaccidents.Pilots and operators hould

review their aircraft’s fuel andenginesystemoperating equirements o ensure hat:

(1) The pilot is completely amiliar with both the airframe and engineoperatingmanuals,especially he chapters oncerning uel management, nginepower settings,useof carburetor

heatan deachof the aircraft’s systemsdesign, ocations,an dcontrols.

(2) The pilot adhereso a ll manufacturer’soperating nstructions,placards,andotherlimitations andavoidsovertemp,overheat,overboost,andoverspeed perations.

(3) The useof the aircraft’s checklistduring norma l and emergency perations sstressed.

(4) Recurrent raining is a continuingprocess. Both pilots a ndmechanics houldkeepabreastof technical nformation related o the aircraft’s fuel, oil, replacement arts, airworthiness

directives,an dmanufacturer’s echnicalpublications.

b. Inadequate Preflight Inspection. A largenumberof enginepower lossaccidents ould

havebeenavoided f the pilot took the time to plan the flight andperformed a goodpreflight.Eachyear the accident ecordsshow a high numberof accidents hat were caused y pilots

runningout of fuel. For good light planning he pilot sho uld ncludeat least he followinginformation in h is or her pre-flight check ist.



6/l S/98 AC 20-105B

To prevent uel selector ailure prior to taxi, exercise he selectorvalve by switching tanksandensuring hat there s fue l flow from eachselected ank to the engine(s). Remember o allow

sufficient time (3 to 4 minutes) or eachcheckas he carburetor/fuel njector lineshold fuel from

the previousselected ank. Do not forget to monitor the fuel pump pressure.At leastonceamonth, check hatme fuel selector’s uel shut off position o ensu re t will stop he fuel flow to

the engine. Remember t will take a few m inutesat low RPM setting or the engine o drain thefuel from the fuel lines/carburetor/fuelnjector and cause he engine o quit. This check s very

importantbecausen caseof an engine ire, the fuel shut off valve will stop fuel flow on thecabinsideof the fire wall, effective ly preventingan eng ine ire from being ed from the aircraft

fuel tanks. If a worn or galled uel se lector s suspected, avea mechanic ubricateor replace hevalve, asneeded.

c. Fuel Contamination. Thereare wo basickinds of fuel contamination,solid and water.Solidcontaminates, uchas sand, ust, and other debriscan be found by inspecting he low

areas/sumpsf each empty andproperly purged) uel tank with an explosionproof flashlight,andby inspecting he fuel system illers andcarburetor/injector n-line filter screen or solid

particulatecontamination. If solid particle contamination ontinues o occur on a frequentbasics, he primary fuel supp liermay be the sourceof the problem.

(1) Water contamination ontinues o be a major causeof fuel relatedaccidents.Thereare hree ways water canenter a fuel system. The irst is condensation, r the reductionprocessin w hich the moisture n warm air is reduced nto liquid water. This phenomenons exactly whatcauseswindows n a warm house o “sweat” during the winter months. In an aircraft,

condensation anhappen nsidea less han full fuel tank. When a temperaturedifferenceoccursbetween he walls of the fuel tank and he air in the tank, water dropletswill form on the inside

top part of the fuel tank walls anddrain down into the fuel. The effects of condensation anbereducedby keeping he fuel tanks full while the aircraft is parked.

(2) The secondway water gainsaccess o the fuel system s through he fuel filler caps.Rain water or snow runoff entry into the fuel system s m adeeasier f the fuel filler capshave



AC 20-105B 6/l S/98

leastonce a day for overall quality and ndicationsof water or other contaminates.Each

inspectionshouldbe documented. SeeAC 20-125, Water in Aviation Fuels, or additionalinformation.)

d. Misfueling Accidents. This occurswhen Jet A, a turbine engine uel is substituted oraviation gasoline. W henJet A contaminates reciprocatingenginepoweredaircraft’s fuelsystem he overall impact s not read ily apparent. Dependingon the amount of Jet A pumped

into the aircraft fuel tank, evena close nspectionof a fuel samplemay not always ndicate

misfueling hasoccurred. Even the enginestart up and taxi may appear o be normal becausehe

Av-gas, that is still in the fuel supp ly system in e and filters from the last flight is not

contaminated nd t usua lly akes he enginea few minutesat relatively high power settings odraw contaminated uel from the selected ank. This is why a largenumber of misfueling

accidentsoccursat high power setting usuallyduring or shortly after takeoff.

(1) Reciprocatingengines hat burn Jet A at high power settings,suffer detonations , apid

loss of power, andhigh cylinder head emperatures,quickly followed by completeengine ailure.

Switching to anotheruncontaminateduel tank as soonaspossibleafter the enginedetonationoccursmay re lieve someof the major symptoms,and he enginemay developenoughpower to

stiely land. Unfortunately, nternal damage o the eng ine hat occurs n the first 10 to I5 seconds

is usually severeenough o requirea tear-down nspectionand engine ebuild. In all cases,follow the enginemanufacturer’s nstructions f the enginehasbeenoperatedwith the wrong

fuel.

(2) The potential for misfueling canbe reduced f the pilot personallyoverseeshe

refueling operation. Thepilot shouldcarefully check he fueling receipt for both the quantity andtype of fuel added. Also checkbeforeand after refue ling for clarity, color, and ndica tionof

water in the fuel. It is suggestedhat the aircraft’s owner/operatorensure hat the fuel filler portsareproperly markedwith the proper type andoctaneof the fuel to be used,and the capacityof

the tank.



6/l 5198 AC 20-105B

f. Exceeding TBO Time. Another causeof engine ailure is allowing the engine o run pastthe manufacturer’s ecommended ime BetweenOverhauls TBO). TBO time is computedby

the enginemanufacturerand s a reliable estimateof the number of hours the enginecouldperform reliably within the established ngineparametersand still not exceed he servicewear

limits for overhau l or major componentparts such as he crankshaft, cam shaft, cylinders,

connec ting ods, and pistons.

(1) Runn ing the enginepast TBO time usually accelerateshe overall wear of the eng inedue o bigger bearing olerances, oss of protective materials such asplating or nitrating on the

cylinder walls, and vibration causedby engine eciprocatingparts that haveworn unevenlyand

are now out of balance.

(2) The TBO times are make and model specific and the recommendedoverhau l imes areusually dentified in the enginemanufacturer’sServiceBulletin o r Letter. For 14 CFR part 91

operationscomp liance o the TBO time is not a mandatorymaintenance equirement. However,for engines n 14 CFR part 121 or part 135 serviceTBO compliance s mandatory. It is

recommended hat TBO be observedby part 91 owners for two reasons: first, an overhaulat TBO

will ensuresafety and reliability, and the second:an engineoverhaul at TBO is usually less

expensive han an engine hat has been un an additional 200 or 300 hours.

g. Poor Operating Techn ique. Reciprocatingengine eliability dependson the engine

operatingwithin a narrow performance ange. This operating angehas specific limits such asI

RPM, fuel flow and mixture settings,man ifold pressure,cylinder head emperature,oil pressure

and temperature hat should not be exceeded.Furthermore, all reciprocatingenginesare

temperaturesensitive. Eng inecylinders and valves can be damagedby thermal shock f the

eng ine s not properly warmed up, prior to full power applications,or the cylinder headscan

crack by allowing the eng ine em perature o cool off too rapidly in long gliding descentsatreducedpower.



AC 20-105B 6/l 5198

the “0” rings in the primer pump arenickedor crackedwhich allows fuel to pass he “0” rings

and nto the cylinder even f the pump handle s stowedand ocked. If this condition s suspected

havea certificated mechanic heck he primer system.

(2) EngineControls. Throttle, mixture, carburetorheat, andpropeller RPM controlsaresimple n designand construction. Eachcontrol is basica!lya flexible m etal wire insidea

stainless teelhousing. Due to the inherent lexibility of the design, f the cablehousing s not

secured t leastevery 12 nches, he cablewill bend n the middle, severely imiting the amountof control movementavailableat the carburetoror propeller governor. Mechanics hou ldensure

that the controls are ubricated,smoothandpositive in operation,and that the lengthof cablemovementensures ull travel and hits the stops. It is suggestedhat mechanics nsure hat

controlswith rod endshave argeareawasherson both endsof the attachingbolt to serveasa

safety in caseof failure of the rod endball.

(3) PropellerGround Strikes. Any kind of a propeller ground strike is a very serioussituation hat requires mmediateattention.Engines hat havesuffereda propellerstrike should

be inspected n accordancewith the manufacturer’s nstructions. Ground strikeshavebeenknown to cause rankshaftcracks,bendpropeller langes,and cause od end bolts to fail.

(4) Internal Failuresof Mufflers. Enginescanexperience ubstantialpower reductionsandeven ailure when the internal bafIling of the muffler breaks ooseand partially coversover

the muffler’s exhaustpipe. Indicationsof this kind of problem are a large eduction n RPM, rich

mixture indication, ough running, vibration, and after firing. It is recommendedhat each

annualor 100hour, the mufIler be inspectednternally for cracksandcondition,

(5) PropellerMaintenance.Propellers eem o get the leastattentionof type-certificatedproducts,yet they handlehigh thrust and orsional oadson every flight, and serveasa tow barfor parking the aircraft. Havea qualified maintenance ersondressout propeller bladenicks,

dents, scratches, tc., as necessary,o prevent fatigue cracks hat could causepropellerbladefailure resulting n power-loss. The dressingof propellerbladesshouldbe done ollowing the



6/l S/98 AC 20-I 05B

(7) SparkPlug Fouling. Sparkplugs hat consistently oul canbe an ndicationof wornrings, excessive ich mixture, impropersparkplug heat ange,shortignition harness, racked

cigarettes,wrong fuel, sparkplug barrels hat are dirty or wet with moisture, gnition timing off,low speed pen&n and dle, improper eaningprocedures nd apid cool down of the engine n

long gliding descents.Frequent nspection,cleaning,gapping,and otation of the sparkplugsmay prove helpful in reducing ou ling. Refer to the Pilot’s OperatingHandbook or approved

engineoperatingprocedures.

(8) Low Cylinder Compression.A compressionest is a procedure n which 80 poundsper square nch (psi) air is introduced nto a cylinder with its piston at top center o determine

how tight the cylinder holds he fuel/air mixture when t is compressed.The pressurized ir iscontrolledwith a differential pressure auge hat has wo gauges. One gauge eadssupplyair,

and he other gauge eads he air pressure n the cylinder. The idea lcompression eadingon thedifferentiation gaugeshouldbe 80/80 psi at top deadcenter. However, the maximum oss of

compressed ir shouldbe no more than 25%, or a readingof 60/80psi. If the cylinder eading slower than 60/80psi reading, hen perform the following test. When he 80 psi compressed ir is

still being ntroduced nto the cylinder, and an experienced ersonholding the propeller so t willnot rotate, isten at the exhaustpipe outlet for an air leak. If an air leak s present, he exhaust

valve or g uideor both is worn and eaking. Perform the same est by listening or an air leak at

the air cleaner, f you hearan air leak then the intakeand/or ntakevalve guide s worn andleaking. To check, f the compression ings are worn, remove he oil d ip stick, and isten at theoil d ip stick tube. If you hearan air leak the piston rings or cylinder walls are worn. A good

visual nspectionof the cylinder canbe accomplished y meansof a borescopeo check orscoringof the cylinder walls andcondition of the valvesand seats.

(9) Air Filters/CarburetorHeat Control, AlternateAir. Unfiltered air, whether t comesfrom a dirty air cleaner, arburetorheatcontrol or alternateair door left on/openduring taxi,

allows dirt, sand,andother debris o be ngestedby the engineand will score he cylinder wallsand ncrease iston ring damage, ausing ower compression eadingsand ncreasing ilconsumptionandblow-by. As a rule of thumb, air filters shouldbe changed t leastoncea year,



AC 20-105B 6/l 5198

(2) Area #2. Cylinder assemb lyncludes he cylinder, piston andpin, intakeandexhaust

valvesand seats. These omponents anbe removed or an n-depth nspectionbut normally aninspectionof the sparkplugsand a compressionest will give a good overview of the cylinder’scondition. Sparkplugs arechecked or wearand fouling. Fouledsparkplugscan ndicate oo

rich a mixture, or compressioning wear.

(3) A rea #3. Accessoriesncluding he magnetos,harness, parkplugs, exhaust,generator, r alternatordrive belts,generatoror alternator,carburetor/fuel n jectionunit andvacuumor pressure ump, areeasily emovab le or inspectionand testingand usuallygive the

pilot an ndicationof their operatingconditionby instrumentation nd gaugesn the cockpit.

b. A generic rend monitoringprogram s found n Append ix 1 and2. Appendix 1 is asampledata form that the mechanicandpilot will fill out. Appendix2 is a sample racking sheetin which all tracked tems collectedon the data orm are isted together n sequenceor easiercomparisonandanalysis.The actualanalysisof the airworthiness tems shou ldbe accomplished

by comparing he readings btainedandnoting the trend asmeasured gainst he manufacturer’srecommendedeading. For example, f the enginemanufacturer ecommended cruiseoilpressure f 55 to 60 psi and he indicated eading n cruisewas 48 psi the mechanic houldcheckoil viscosity, oil quantity, oil relief valve setting,oil filter, bearingwear, ndicationsof blow

by/leaks,and the accuracyof the oil p ressure auge. The mechanic analso crosscheckwith the

resultsof the oil ana lysis, ylinderhead emperatures, il temperatures, parkplug condition,andcylinder compressioneadings.

NOTE: A trend monitoring program is only as good as the information that

it collectsand analyzes. Before incorporating an engine rend monitoringprogram, the owner/operator shou ld ensure that the following aircraft’sinstruments and gaugeshave been ested for accuracy; RPM gauge,oilpressure, oil temperature, cylinder head temperature, Exhaust Gas

Temperature (EGT), fuel gauges,and manifold gauge, f applicable.

c. An engine rend monitoring program s requiredundercertainprovisionsof part 135



6/l 5198

AC 20-105B

Appendix 1

APPENDIX 1. ENGINE TREND MONITORING DATA FORM

INSTRUCTIONS: Form is to be filled out by both the pilot and mechan ic prior to or

durjng inspection interval. Asterisk (*) items are pilot functions.

DATE OPERATOR“N” NUMBER

MODEL NUMBER

TOTAL TIMETOTAL TIME SINCE OVERHAUL

SIN

MFG.TYP E OF OIL USED

HOBBWTACH

AREA #l ENGINE CASE COMPONENTS:

OIL ANALYSIS:DATE TAKEN LABORATORY

SILICONALUMINUM

IRON

CHROMIUMCOPPER

*OIL PRESSURE@ CRUISE RPM*OIL TEMPERATURE @ CRUISE RPM

*STATIC RPM (FIXED PITCH)*MANIFOLD PRESSURE@ TAKEOFFOIL FILTER CONDITION:

OK

TAKE OFF RPM(CONT. PITCH)

MAGNETIC PARTICLES QUANTITY



AC 20-105B

Appendix 1 6/l 5/98

APPENDIX 1. - continued

ENGINE COMPRESSIONRESULTS:

#l#2#3#4

#5#6#7

#8

SPARK PLUG CONDITION: 1 = good 2 = worn 3 = oil fouled 4 = carbon ouled

#l CYLINDER TOP

BOTTOM

#2 CYLINDER TOP

BOTTOM

#3 CYLINDER TOPBOTTOM

#4 CYLINDER TOP

BOTTOM

#5 CYLINDER TOP

BOTTOM



OPERATOR TYPE OF OIL USED

“IT’ NUMBER SiN

MODEL NUMBER MFG.

DATE:

TOTAL TIME:

TOH:INSPECTION INTERVAL (50/l OO/ANNUAL):

AREA #l

OIL ANALYSIS:

ALUMINUM

IRON

COPPER

SILICON

INSP. 1 INSP. 2 INSP. 3 INSP. 4 INSP. 5 INSP. 6 INSP. 7 INSP. 8

CHROMIUM

OIL PRESSURE

OIL TEMPERATURE

OIL FILTER

OIL SCREEN

OIL CONSUMPTION



AREA #2

CHT

EGT#2

JNSP. 1 lNSP. 2 INSP. 3 INSP. 4 INSP. 5 INSP. 6 INSP. 7 INSP. 8

COMPRESSION

\I

#6

#7

#8

DATE SPARK PLUG REPLACED @ ENGINE HOURS



SPARK PLUG CONDITION: 1 = good 2 = worn 3 = oil fouled 4 = carbon fouled



FUEL BURN

GPH

lNSP. 1 MSP. 2 INSP. 3 MSP. 4 INSP. 5 MSP. 6 INSP. 7 INSP. 8

AREA #3 ACCESSORIES

MAGNETO DROP @1500/1700 RPM

INSP. 1 INSP. 2 lNSP. 3 INSP. 4 l-tap. 5 MSP. 6 MSP. 7 INSP. 8

RT LT RT LT RT LT RT LT RT LT RT IT RT LT RT LT

VACUUM GAUGE @

1500/1700 RPM

ELECTRICAL VOLT/AMP @J

2100 RPM

n

MSP. 1 INSP. 2 INSP. 3 INSP. 4 INSP. 5 INSP. 6. INSP. 7 INSP. 8

h

AIR FILTER CONDITION

DATE AIR FILTER REPLACED

INSP.l 1 INSP.2 1 l-NSP.3 1 INSP.4 1 lNSP.5 ) INSP.6 1 INSP.7 1 lNSP.8I I I I I I I

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