DATA SUMMARY - Ministerio de Fomento · main rotor and the right horizontal stabilizer. There was a significant deformation on the stabilizer where it was supporting the weight of

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REPORT A-024/2013

DATA SUMMARY

LOCATION

Dateandtime Sunday, 4 August 2013; at 19:50 h1

Site Puebla del Maestre (Badajoz, Spain)

AIRCRAFT

Registration EC-KIE

Typeandmodel AIRBUS HELICOPTERS AS-350-B3

Operator Inaer

Engines

Typeandmodel TURBOMECA ARRIEL 2B1

Number 1

CREW

PilotAge 28 years old

Licence CPL(H)

Totalflighthours 1,250 h

Flighthoursonthetype 100 h

INJURIES Fatal Serious Minor/None

Crew 1

Passengers

Thirdpersons N/A

DAMAGE

Aircraft Significant

Thirdparties None

FLIGHT DATA

Operation Aerial work – Commercial – Firefighting

Phaseofflight Landing

REPORT

Dateofapproval 12 November 2014

1 Alltimesinthisreportarelocalunlessotherwisespecified.

Report A-024/2013 Addenda Bulletin 2/2015

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1. FACTUAL INFORMATION

1.1. History of the flight

OnSunday,4August2013,anAirbusHelicopters2AS-350-B3aircraft,registrationEC-KIE, was involved in efforts to fight a forest fire between the towns of Pallares andLlerena(Badajoz).12

Aftermaking severalwater drops, thepilot proceeded to thebase atCalera de León(Badajoz)torefueltheaircraftandtaketherequiredrest.

Duringhisbreakhewasinformedthatthefirewasundercontrol,thatnofurtherwaterdropswerenecessaryandthathecouldreturntohisusualbase,whichwaslocatedinValenciadeAlcántara(Cáceres).Asaresult,heproceededtoplacetheBambibucketinitsbasketandat theconclusionofhis restperiod,he tookoffandset course for theareaofthefiretopickupthefirefightingsquadandreturntobase.

As he approached the fire area he received a call on the radio from the coordinatoraskinghimtoflyoveracertainspot tosee if thefirehad reflashed.Heproceeded tothe indicatedareaandsawthatthefirehadindeedreflashed,astherewereflames inthe area.He reported this to the coordinator,who instructedhim todropwateroverthearea.

Heradioedthesquad leaderto informhimofhisnewordersandthathewould landsomewhereneartheir locationsothattheycoulddeploytheBambibucket.

HesawasectionoftheoldEX103roadand,believingithadthenecessarycharacteristicstoland,headeddirectlytowardit.

He landed normally and verified that the helicopter was properly supported on theground.Severalminutes later thefourmembersof thesquadapproachedandtwoofthem went inside the helicopter. The pilot informed them that they had to exit anddeploytheBambibucket.Threeofthemproceededtotakethebucketoutofitsbasketandlaiditoutinfrontofthehelicopter.

After this two of them moved some distance away from the helicopter and a thirdstayedalongsidetheBambibuckettotest itselectricallyoperatedopeningsystem.

As the pilot stated, he saw the firefighter walk to the front of the helicopter anddisappear underneath the nose, possibly to check something in the area where theBambibucketis latchedtothehelicopter.

2 AirbusHelicoptersisthecurrentnameoftheaircraftmanufacturerformerlycalledEurocopter.

Addenda Bulletin 2/2015 Report A-024/2013

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Figure 1. Sketchofthepositionofthehelicopterandofthesquadmembersatthestartoftheevent

Just thenthepilot felt thehelicopterstart tobouncewith increasing intensity.Fearingfor thefirefighterunderneaththehelicopter,hedecidedtotakeoff.Hepulledonthecollective and the helicopter started to climb, though the abrupt motions continuedevenmoreintensely.

The firefighter who was underneath the helicopter hooked himself to the right skid,remainingattached to it until hewasable to takeadvantageof a forwardmotionofthehelicoptertofreehimself.

Thepilot triedto regaincontrolof theaircraftbutwasunable to, losingallcontrolofthehelicopter,whichendedupturnedonitsrightside.

Thepilot,whowasuninjured,stoppedtheengineandcutthefuelandpower.Hewasabletoexitthehelicopter,aidedbythemembersofthesquad.


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1.2. Injuries to persons

The firefighter who was underneath the helicopter was slightly injured when he wascut,probablybyseveralbladefragmentsthatdetachedduringtheaccidentandimpactedhim.

1.3. Damage to aircraft

Theaircraftsufferedsignificantdamage,whichprimarilyaffectedthefollowingareas:

• Landinggear• Mainrotor• Anti-torquerotor• Tailcone• Horizontalstabilizer

1.4. Personnel information

Age: 28yearsold

Nationality: Spanish

License: CPL(H),validuntil28/01/2018

Ratings: • AS350/EC150/SPvaliduntil30/04/2014 • Forestry(firefightingonly)validuntil30/09/2014 • Class1medicalcertificatevaliduntil13/07/2014

Totalflighthours: 1,250h

Flighthoursontheaircrafttype: 100h

Regarding his experience in firefighting, the 2013 was his third campaign, havingparticipatedintheonesoftheprevioustwoyears.

Activity

Thepilot’s duty schedule for the June and July preceding the accident is as shown inthe timelinesbelow,withdutydays represented inamberandoff-dutydays shown ingreen.

JUNE 2013

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30


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JULY2013

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

The pilot was on duty during the four days in August leading up to the day of theaccident.

Flight hours

• Intheprevious90days:30:34h• Intheprevious30days:07:21h• Intheprevious24h:03:00h

Onthedayoftheaccidenthehadcommencedhisflightactivityat16:40.

Training

• 09/04/2013 Recurrent ground training and check on firefighting operations. ESP-OPS-H-TA-F-D02

• 30/04/2013 TrainingandchecktorenewtheAS350typerating.• 31/05/2013 In-flightfirefightingtraining.FormESP-OPS-H-TA-F-D01

1.5. Aircraft information

1.5.1. General information

Manufacturer: AIRBUSHELICOPTERS

Model: AS-350-B3

Serialnumber: 4286

Yearofconstruction: 2007

Airworthinessreviewcertificate: Validuntil12/07/2014

Engines,number/manufacturerandmodel: One(1)/Turbomeca,Arriel-2B1,s/n:23299

Emptyweight: 1,275kg

Maximumtakeoffweight: 2,250kg


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Dimensions: • Mainrotordiameter:10.69m • Total length:12.94m • Fuselagelength:10.93m • Totalheight:3.14m

Aircrafthours: 1,355h

Enginehours: 1,211h

Landings: 4,066

Maintenancestatus:3

Inspection type Date Hours Remarks

Basic(1,200h/4year) 30/05/2012 1,237 Enginereplaced

100h/annual 04/06/2013 1,311 Vibrationsmeasured2

Monthly 04/07/2013 1,345

Modificationsmadetotheaircraftafter leavingthefactory:

Approval ref. Title

BI-002-06 InstallationofPowerfillandSacksafoam

CMA165-BI Installationofexternalloudspeaker

CMA107-1 InstallationofP2500VHF-FMradio

CMA163-BI Installationoffleettrackingequipment

CMA108-BI Bambybucketopeningsystem

STCSR00213NY Dartutilitybasket

SB25.00.78 Installationofcablecutter

M12/053/24-BI PortableGPSpowersupply

1.5.2. Information on the flight manual

IntheTakeoffsection(4.4),anoterecommendsadjustingthefrictiononthecyclicandcollectivecontrolssothatthepilotfeelsresistancewhenmovingtheflightcontrols(seeFigure2).

3 Vibrationsweremeasuredinthemainrotor,tailrotorandtailrotorgearbox.


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Figure 2. Beforetakeoffchecklist

Additionally, the enginepre-start checklist (4.3.1) in the Start-up section (4.3) includestheactiontoadjustthefrictiononthecyclicandcollectivecontrols(items17and18).

1.6. Wreckage and impact information

1.6.1. Information on the accident site

TheaccidentoccurredonasectionoftheoldEX-103road.

As figures 3 and 4 show, this segment of the road is cut off at either end by a leftturn inthenewroad,which iscut intothehillsidetotheeastoftheoldroad,whichmadearightturnatthis location.Onthewestsideoftheoldroadisawoodedareacontaining mainly oak trees. The elevation of the new road is below that of the oldonebyabout4m.

Thissegmentoftheoldroadbasicallycomprisesaplatformwithadistinctlycurvedandelevatedgeometrywithrespecttothenewroad.


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Figure 3. Aerialviewoftheaccidentsite

Figure 4. Viewoftheaircraftwreckage

The part where the helicopter landed (central area of the segment) has a maximumwidthofabout10mmeasuredfromtheedgeofthewoodedareatothestartoftheincline.Thepavementinthisareaismixed,withdirtateitherendandasphalticconcreteinthemiddle.Thegradientinthisareafromwesttoeast isrising-falling-rising.


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1.6.2. Wreckage information

Theaircraftwasonitsrightsidealmostattheedgeoftheincline,withitslongitudinalaxisfacingNorth(005°).Thehelicopterwasrestingontherightsideofthecockpit,themainrotorandtherighthorizontalstabilizer.

Therewasasignificantdeformationonthestabilizerwhereitwassupportingtheweightofthehelicopter.

Thetailrotorhaddetachedfromtheaircraftandwasontheditchofthenewroad,whichrunsalongthebottomoftheincline.Oneofthetwobladesontheanti-torquerotorhaddetachedandwasalsoatthebottomoftheincline,but20msouthoftherotor.

Themain rotor still had someblade segments attached to it.Mostof thebladeshadfracturedduetotheimpactandthedetachedfragmentswerescatteredtotheeastandwestofthemainwreckage.

Partof the right skidhaddetacheddue to two fractures,oneon the skid itself, rightbehindtheforwardcrossbar,andtheotherontherearcrossbar.Thedetachedfragmentwasnexttothemainwreckage.

Theaircraft’stailskidhadalargenumberofperpendicularmarkingsonit.

Thetailguard,locatedattherearofthetailboomandwhoseendsareattachedtothefuselageandtothebottomoftheverticalstabilizer,wasbrokeninthemiddle.Thepartthat remained attached to thefuselage was rotated 90° clockwiseout of its normal position as seenfromabove.

There was a nearly circular markthatsurroundedmostoftheaircraftand where the right horizontalstabilizerwasfound.

Surrounding the circular markdescr ibed in the precedingparagraph, especially to the southof the aircraft, was another, faintmark.

Next to it was yet a third faint,longitudinal mark facing west(heading265°). Figure 5. Close-upoftheellipticalmark


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Therewasanellipticalmarkmeasuringabout60×40cmneartheareawheretherearcrossbarhadfractured,theendofwhichexhibitedsignificantimpactdamage.

In the area near the nose of the aircraft there were several deep, parallel marks thathadbeenmadebystrongimpacts.

Therewerenoclearmarksindicatingwherethetailrotorhadimpacted.

Themechanismusedtoadjustthefrictionofboththecyclicandcollectivecontrolswasfound to be in the position of minimum friction. The collective pitch control was notlockedinits lowerposition.

1.6.3. Inspection of the aircraft

Theaircraftwastakentotheoperator’sfacilitiesforthepurposeofsubjectingittoamoredetailed inspection.Aiding inthis taskwastheBureaud’Enquêtesetd’Analysespour laSécuritédel’AviationCivile(BEA),whichistheFrenchauthoritychargedwithinvestigatingcivilaviationaccidentsandincidents,andtheaircraftmanufacturer,AirbusHelicopters.

1.6.3.1. Card AMM 05-50-00, 6-20

In lightofthe informationreportedbythepilotregardingthebehavioroftheaircraft,it was decided to inspect it as per the instructions on “card AMM 05-50-00, 6-20.Actions to be taken in the event of abnormal behavior of helicopter on the ground,with rotor spinning”,whichdescribes theparts of thehelicopter tobe inspected if itbehavesabnormallywhileonthegroundwiththerotorsturning.Theseparts include:

• Mainrotor• Gearbox• Landinggear• Starflex• Tailrotor

Duetothedamagesufferedbythehelicopterduringtheaccident, itwasnotpossibletodoall of the actions indicatedon the card, especially those involving the rotors.Asummaryofthefindingsisprovidedbelow.

Main rotor head

• Starflex.Overall itwasheavilydamagedduetotheimpactofthebladesagainsttheground,whichcausedthearmontheredbladetofracture.Thedamagefoundwasconsistentwith the impactof thebladesagainst thegroundatpower.Noevidenceofpreviousdamagewasfound.


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• Ball joint.Due to the impactsof thebladesagainst theground, theball joint couldnot be checked. A visual inspection, however, did not reveal any abnormalities orsignsofexistingdamage.

• Sphericalthrustbearings.Thesehadcomeloosefromthestarflexduetotheimpacts.Theelastomersdidnotexhibitcracks,detachmentsorprotrusions.

• Frequencyadapters.Theywereseverelydamagedbytheimpacts,thoughnoevidenceofanexistingfaultwasfound.

Main gearbox suspension

• Laminatedstops.Thesewerestillproperlypositionedanddidnotexhibitanyshifting,bending,separationsordamage.

• Gearboxsuspensionbars.Thesewerestillproperlypositionedanddidnotexhibitanyshifting,bending,separationsordamage.

Landing gear

• Landing gear. Due to the impact it was partially fractured and bent. As a result, itwasnotpossibletodothespecifiedchecks.Thedifferentpartscomprisingthegear,however,withtheexceptionofthebrokenanddetachedskidsegment,wereproperlyconnectedandshowednosignsofcrackingorcorrosion.Therewasalsonoevidenceofdamagefrombeforetheaccident.

• Landing gear attachments. The gear was properly connected to the helicopterstructureandtothedampersandshowednosignsofwarping,crackingorcorrosion.

• Bladesat the rearof the skids.Their function is to reduce the riskof resonanceonthegroundwhilelanding,thoughtheyhavenoeffectoncetheaircraft isrestingontheground. The inspection consistsofmeasuring thedistance from theendof thestripandtheextensionofthetoppartoftheskid,whichmustnotexceed85mm.

Figure 6. Leftrear(left)andrightfront(right)attachments


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Although these checks were not valid in this case due to the deformations causedduring the accident, they were carried out for information purposes, yielding thefollowingresults:

— Leftskid:89mm — Rightskid:73mm

• Dampers. They were properly attached to the landing gear and exhibited noabnormalities.

Theyweredetachedforanoperationaltest,whichconsistsofmeasuringhowlongittakesthedampertostretchagiven lengthundera loadof20daN,thistimebeinglimitedtobetween7.1and12.5s.Thistestwasrepeatedseveraltimes,yieldingthefollowingresults:

— Leftdamper:9.7-9.4s — Rightdamper:9.8s–9.6s–9.7s

Anti-torque rotor

Thebladeswere severelydamaged from the impactwith theground,which impededcarrying out the required inspections. No evidence was found, however, of any pre-existingdamage.

Anti-torque gearbox

As with the blades, the gearbox was severely damaged, which made it impossible tocarryout the required inspections, thoughnoevidencewas foundof anypre-existingdamageeither.

1.6.3.2. Cyclic and collective pitch controls

As stated in 1.6.2, the friction on the cyclic and collective controls was set to theminimumonboth.

The device that is used to lock the collective pitch control at its lowest position wasverifiedtobeworkingproperly.

Thethrottlegripwasfoundinthe“flight”position.

1.6.3.3. VEMD4 and DECU5

Thesetwounitsstoreinformationoncertainengineandrotorparameters,andanyoverlimitsoftheseparametersthatcouldbeofusetoaninvestigation.

4 VehicleEngineMonitoringDisplay.5 DigitalEngineControlUnit.


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Inordertodownloadtheirdata,theywereremovedandsenttotheBureaud’Enquêtesetd’AnalysespourlaSécuritédel’AviationCivile(BEA),wheretheyfirstunderwentaninspectioninanefforttodeterminewhethertheirconditionallowedadirectreadingofthedatastoredonthem.

Afterthisinspection,itwasconcludedthatadirectreadingwasfeasible,sobothunitswere sent to their respective manufacturers, the VEMD to Airbus Helicopters and theDECUtoTurbomeca.

VEMD

The unit was energized on the test bench in accordance with BEA/Airbus Helicoptersprocedures.All of thedata recordedon theunitweredisplayeddirectly on its screenandphotographed.

Thedataforthelastflightrecordedwereassociatedwithflight1878,whichlasted16minutes6.Thisflightrecordedonefaultandoneoverlimit.

Thefaultinvolvedadiscrepancyinthepositionoftheanticipatorpotentiometeronthecollective.Therelevantparametersrecordedforthisfaultareasfollows:789

Time Description NG6 (%) Torque (%) T47 (°C) NF8 (rpm)

15:17min COLLPITCHPOTL 97.5 127.3 773 271

Duringthisflighttheenginetorquewasoverlimitedseveraltimes,themaximumvaluebeing128%.Thedurationoftheseviolationswereasfollows:

1sbetween105%and110%.3sbetween110%and118%1sbetween118%and128%

DECU

TheinformationcontainedonthisunitwasdownloadedattheTurbomecatestbench.

Fault block number 1 was the most recent and was associated with start-up number8576. This fault block had been recorded 968 s (16:08 min) after the DECU wasenergizedandcontainedthefollowingmessages:

6 TheVEMDstartscalculatingtheflighttimewhenthespeedofthefreeturbineexceeds60%.7 Measuredrotationspeedofthegasgenerator.8 Averagetemperatureattheexitofthegasgeneratorturbine.9 Rotationspeedofthefreeturbinecalculatedinrotorspeed.


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• ADCchannelB/OSS;DECU ThismessageinformsofadiscrepancyintheanalogtodigitalconverteronchannelB.• Steppermotor/OSS;DECU Thismessageconcernsthefuelflowactuator.• Collectivepitchmeasurement/AS;DECU Thismessageindicatesthatthevalueoftheanticipatorpotentiometeronthecollective

isout-of-specification.Thismaybeduetoadefect,anexcessoratransient.

1.7. Eyewitness interviews

1.7.1. Pilot’s statement

HebeganbystatingthatonthedayoftheeventhewasathishomebaseinValenciadeAlcántara(Cáceres).At16:25hewasnotifiedofthepresenceofafireinLaPuebladelMaestre(Badajoz).

About 10 to 12 minutes later he took off from the base, carrying onboard the four-personfirefightingsquad.

Theyreachedthefiresiteandhesetthehelicopterdownafterfindingaplacetoland.After the firefighters deployed the Bambi bucket, he took off. The squad remainedbehindtofightthefirefromtheground.

Thefirefightingcoordinatorinstructedhimwheretomakethewaterdrops.

Aftersometime,hewenttothebaseinthetownofCaleradeLeón,whereheplannedtorefueltheaircraftandtakehis legallyrequiredbreakeverytwodutyhours.

Whilehewas thereanotherhelicopterarrived. Shortly thereafterhewasnotified thatthe fire was under control and that no more water drops were needed, meaning hecouldreturntohishomebase.

Asaresult,theypickeduptheBambibucketsonbothhelicoptersandplacedthemintheirrespectivebaskets.

Oncehis rest timewas complete,he tookoffen route to theareaof thefire topickupthesquadandreturntoValenciadeAlcántara.

While in the vicinityof thefirehe receiveda call from the coordinator informinghimthat thefire appeared tohave reflashedandaskinghim toflyover a specific area toconfirmthisreport.

Hewent to thespecifiedareaandconfirmedthat thefirehadnotonly reflashed,butthattherewereflames.Hereportedthisinformationtothecoordinator,whoinstructedhimtomakewaterdropsovertheareatoextinguishthefire.


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HeradioedthesquadleadertoconveythenewinformationandtoinformhimthathewouldbelandingsomewhereneartheirlocationsotheycoulddeploytheBambibucket.

Heflewovertheareawherethesquadwas,whichwasascrublandcoveredmainly inoaktrees.Theareaofferedfewspacessuitableforlanding.

Hesawasegmentofanold road thathedetermined tobesufficientlywell suited toconductasafelanding.

Heapproacheditflyingfromthesouth-southwestoverthenewroadandashenearedthesitewherehehadchosentoland,heturnedrighttohoveroverthesite.

He landedwith theaircraftpractically facingwest,as thewindwascomingfromthatdirection.

Hecalculatedthat inthat landingposition,theaircraftprotrudedoutsidetheplatformthattheoldroadpassedthrough.Ontheotherside,despitethesmalldimensions,hehadsufficientseparationfromobstacles,whichwasprimarilytheoaktrees.

Hewaitedthereonthegroundforafewminutesuntilthesquadarrived.

Theyopenedthehelicopterdoorandtwofirefightersclimbedonboard.Heradioedtheleadertoremindthemthattheywerenotreturningtobaseyet.Hethenturnedaroundtoinformthetwofirefighterswhohadclimbedonboardthattheyhadtogetout.

TheydidandthentheyproceededtotaketheBambibucketoutof itscarryingbasket(this operation requires threepeople). They then laid it out in front of and slightly totherightofthehelicopter.

After this, two of them went to one side and the third remained next to the Bambibuckettotest itselectricalopeningsystem.Thepilotstatedthatthistest isperformedeverytimethebucketisremovedfromitsbasket.

Atonepointhesawafirefighterwalkingtothefrontofthehelicopterandthenbenddowntogoundertheaircraft.

He had the collective control in its lowest position and the throttle grip in the flightposition.

Almost instantlyhe felt thehelicopterstart tobounce.Thedescriptionhegaveof thebounceswasthat theskidsdidnot riseupsimultaneously,but ratheralternating, thatis,thehelicopterfellfirstononeskid,bouncedup,andfellontheother,andsoon.

Fearing for the firefighter underneath the helicopter, he pulled on the collective. Hecould not specify whether this action was fast or not, or how he commanded thepedals,thoughhesaidthatapplyingthepedalwhilepullingonthecollectiveisalmost


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instinctivetohim.Hecouldnotstatehowmuchinputheprovidedtothepedal,butheensuredhavingdoneit.

He thought that thehelicopterhadstarted toclimb, though thisdidnotdiminish thebouncingaction;onthecontrary,thebouncingwasbecomingmorepronounced.

He tried to control the aircraft but was unable to, eventually becoming completelyuncontrollable.

Hecouldnotspecifyhowthehelicoptermighthavemovedorturnedafterwardsbeforeitendedupturnedoveronitsrightside.

Hecutthefuel,stoppedtheengineandturnedoffthepower.

The firefighters responded quickly and told him that smoke was coming out of theengine.Hepunchedoutoneof thecockpitwindowsandgave themtheextinguisherinthecockpitsotheycoulddischargeitontheturbine.

Oncetheextinguisherwasdischarged,theyopenedthehelicopterdoorandhelpedhimexit.Onceoutsidehewasrelievedtoseeallfourmembersofthesquad.

Shortlyafterwardstheynoticedthatoneofthefirefightershadbloodstainsonhisbackthathadbeencausedbylacerations.Sotheylaidhimfacedownandnotifiedemergencyservices.

WhenthefirefightersarrivedthesquadaskedthemforaCO2extinguisher,whichtheydischargedontheturbine.

1.7.2. Squad members

No. 1

Hewas thenewestmemberof the squad,havingbecomea squadmemberonly twomonthsearlier.

Bythetimetheyreachedtheaccidentsite,thehelicopterwasalreadythere.Sincetheythoughttheyhadcompletedtheirmissionandwerereturningtotheirhomebase,theyproceeded to stow their tools in the Bambi bucket basket. They then opened thehelicopterdoorandtwoofthemclimbedonboard.Thepilot turnedtothemandtoldthemtoexitbecausehehadtomakemorewaterdrops.

TheygotoutandthreeofthemtookouttheBambibucketandlaiditoutinfrontandslightlytotherightofthehelicopter.


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Hethenproceededtotakeoutsometoolsandtakethemtotheleftofthehelicopter,specifically,toanareawithfactory-madeguardrailsfortheoldsegmentofroad.

Thesquadleaderwasinfrontofthehelicoptersohecouldsignalthepilot.

Anotherfirefighterwasnext to theBambibucket inorder to test itsopening system,andthethirdwasclosingthebasketforthebucket.

After leaving the tools, he turned toward thehelicopter and saw itwas climbing.Heestimated it climbedabout twometersand then itmoved forwardandbackward.Hethenthoughtitturnedslightlytoitsleft,sincehecouldseethepilot’sface.Andthatiswhen the tail rotor impacted the ground, though he could not pinpoint the exactlocationoftheimpact.

Thehelicopterstartedrotatingaboutitselfveryquickly.Hethoughtitmadeacompleterevolutionandthenthemainrotorbladesimpacted.

Hesawoneofhiscolleaguestryingtoavoidthehelicopter,atonepointnoticinghowhegrabbedtherightskidbeforelettinggo.

Asfor thetestof theBambibucket,hestatedthatsomepilotsdonot like toanddonotdoit,whileothersdocarryitout.

He was also asked to watch a video of a helicopter of the same model experiencinggroundresonancetoseeifthebehaviorofthehelicopterinthevideomatchedthatoftheaccidenthelicopter.

Thissquadmemberindicatedthatthetwobehaviorswerecompletelydifferent.

No. 2

Hebeganbysayingthatthehelicopterhadcomefromrefuelinginanearbybase,andthatthefirecoordinatorhadtoldthemthatthefirewasundercontrolandtheycouldreturntotheirbase.

Theyspoketothepilot,whosaidthathewould landinthesameplaceaswhentheyhadcomefromthebase,butintheendthepilotdecidedtolandelsewhere.

Thesitetheyhadusedupontheirarrivalhadbeenalevelpatchbetweentheoaktreesthat was a bit further away from them than the accident site, though the differencewas not significant. As concerns the features of the two sites, he indicated that theformerwasbetterasitwasmuchwider.

They arrived at the spot where the helicopter had landed and saw that it was fairlysmall.


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Atfirsttherewassomeconfusion,sincetheythoughttheywerereturningtobase.Thatiswhytheyputawaythetoolsandtwooftheworkersclimbedonboard.Thatiswhenthepilot radioedhimto informthemthat theywerenotgoingbackandthathehadtomakemoredropssincethefirehadreflashed.Hesawthepilotturnaroundtowardthetwofirefighterswhohadclimbedonboard,afterwhichtheygotout.

HewasstandinginfrontofthecockpitandinstructedthesquadtoremovetheBambibucketfromitsbasket.Oncedeployed,oneoftheworkersstayedalongsidethebuckettodotheoperationaltestofitselectricalopeningsystem.

Thehelicopterrosesuddenly.Heguesseditmusthaverisensome25cm.Thenitmovedforwardandbackwhilebouncing.Hestateditalsorotated180°totheright(thenoseofthehelicopterturnedtotheleftoftheeyewitnesswhowasstandinginfrontofhim).

Asregardstheplacewherethetailrotorimpacted,hecouldnotspecifythelocationashewasonlyingdownonthegroundandhadnotseenit.

Concerning the test of the opening system, he stated that there are B3 pilots (samemodelastheaccidenthelicopter)whoprefernottodoitandonlycheckitonthefirstwaterdrop.On theBell 407,however, theyalways check it sincewhen thebucket isstowed in the baggage compartment, it is disconnected from the load hook and theelectricalsystem,anditallhastobereconnectedwhenit isdeployedagain.

No. 3

Theyarrivedat theplacewhere thehelicopterhad landed.Since theirorderswere toreturntobase,theyproceededtostowtheirtools inthebasketfortheBambibucket,whichwasalreadystowed.

Thesquadleaderthentoldthemtheyhadtotakeoutthebucketfromitsbasket,whichtheydidbeforelayingitoutinfrontofandtotherightofthehelicopter.

He kneeled down next to the bucket to test its electrical opening system. This testrequiresthepilottopresstheopeningbuttonwhilethefirefighterpullsonthecable.Ifthesystemworksproperly,whenthepilotpressesthebuttonthecableshouldrelease,and when pulling manually on the cable it should unspool a certain length. He thenreleasesitandthecableshouldreel intothesamepositionasatthestartofthetest.

Hestatedthattodothetestcorrectly,hehastokneeldownalongsidethehelicopter.

Onthedayoftheaccidenthewasalreadyinthatpositionawaitingthesquadleader’ssignal to pull on the cable. He then heard a noise he thought was the skid scrapingagainsttheground.Suddenlythehelicopterbouncedforward,thatis,towardhim.


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Hethrewhimselfdownandrolledaroundonthegroundtryingtoavoidthehelicopterandfleethearea.

Thehelicopterclimbedalittle,butitwasasthoughitcouldnottakeoff.Thiskepthimfromgettingaway.Atonepointthehelicopterrosealittlemoreandhethrewhimselfattherightskid,whichhemanagedtograb.

Heheldon to theskid fora fewseconds thoughhis feet remainedon thegroundatall times, since the helicopter did not climb much. He took advantage of a forwardmotion of the helicopter to let go of the skid and propel himself to the right. Heremainedonthegroundandheardbangingnoises,thoughhedidnotknowwhereorwhattheirsourcewas,asheremainedonthegroundandcouldnotsee.

Hestooduptorunawayandfeltsomethinghithimonthelegandaburningsensationonhisback.

Hemanaged tomake itdown to thewoodedarea to the rightofhelicopter (lookingforward),andwhenthehelicopterstopped,heclimbedoncemoretotheflatarea.Onreachingit,hesawthathiscolleagueswerehelpingthepilotexitthehelicopter.

Thispersonwasaskedtowatchthesamevideoassquadmemberno.1.

Hewasofthesameopinionashiscolleagueandagreedthatthetwobehaviorswerenothingalike.

No. 4

Hebeganby stating that thepilot alonehad selected theplacewhere thehelicopterlanded, and that it was different from the place they had used to land when theyarrivedfromthebaseinValenciadeAlcántara.

They arrived at the site and started stowing their tools since they had instructions toreturntobase.Thesquadleaderthentoldthemtheyhadtotakeoutthebasketsincethecoordinatorhadorderedmoredrops.

Betweenanotherfirefighterandhimthey tookout thebucketand laid itout in frontofandtotherightofthehelicopter.

In the meantime another crewmember took out the tools. Once the bucket was laidout,oneofthefirefightersremainedalongsideittodothetest.

He went to the left side of the helicopter to close the basket used to transport thebucket.Ashedidthis,hesawthehelicopterrise(about20or30cm),andthattheleftskidwasbrushingupagainsthis legs.Thehelicoptersuddenlybouncedtotherear.


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Heshoutedtohiscolleaguesto“getout”and“getdown”andranintothewoodsinfrontofthehelicopter,wherehedroppedtothegroundandrolledtotheedgeofthewoodedarea.

Hesawthesquadleadertakecoverbehindtheguardrails.

Oncethehelicopterstopped,hewalkedtoward it.Uponreaching ithenoticedthat itwas leaking a small amount of fuel and that there was smoke coming out of thecockpit. He saw that the pilot was conscious and asked him for the extinguisher todischargeitontheturbine.

Whenaskedaboutthepositionoftheskidsbeforethehelicopterstartedtobounce,hestatedthattheleftonewaspartlyonthepavedareaandpartlyonthedirt.

Asforthetestoftheopeningsystem,hestatedthatnotallpilotsdoit.

1.8. Flight recorders

The aircraft was not equipped with a flight data recorder (FDR) or a cockpit voicerecorder(CVR),neitheronebeingrequiredforthisaircrafttype.

1.9. Organizational and management information

1.9.1. Test of the bucket’s opening system

Chapter 3 of the Special Operations Manual on firefighting (MOE) contains theinstructions of an operational nature to be used by flight crews during firefightingoperations.

Item 3.8.1 in this manual, called “Operating with the Bambi bucket”, states thefollowing:

Onreaching thedropsite, thepersonnelwilldisembarkand takeout theBambibucket, lay itoutontherightsideofthehelicopter,ensuringthatthecablesarea safedistanceaway fromthe landinggear inhelicopterswithwheeledgear,orunderneath the skid in helicopters with skis, to keep it from tangling up in thegear. The bucket is to be in a horizontal position with the fill nozzle facing thehelicopter.Oncethebucketislaidout,oneoftheFFSmemberswhooperatethebucket will give a signal to start the water drop test, and another member willchecktheopeningmechanismbypullingmanuallyonthereleasecableandthenensuringitreturnstoits initialposition.


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Following this test they will signal that everything is OK and join up with theremainingmembersoftheFFS.Thisentireoperation,aswellasthestowingofthebucketandinsertingitintothecabinattheendoftheoperation,willbesupervisedatalltimesbythesecondcrewmember,ifthereisone,orbytheFFSleaderifnot.

Additionally, item 3.7.4.1 in this same manual, titled “Preliminary check of theperformanceandtheelectricalreleasesystem”,providesthefollowinginstructions:

Theperformanceoftheh/candtheoperationoftheelectricalwaterdropsystemmustbecheckedwhenwater isfirsttakenon.Thiswillbedonebytakingonaslittlewateraspossibleandcheckingengineparameters,temperaturesandpressureswhile hovering, ensuring they are all within limits. Ensure also that no warning/alarmlightsareonandthatenoughreservepowerisavailabletotakeoff.Attheconclusion of this check, the electrical button to discharge the water will bepressed to ensure that the electrical discharge system works properly. This isimportantsinceifthewatercannotbedroppedonthefireduringadroppingrunduetoafaultyelectricalconnection,anundesirablesituationwillresultfrombeingunabletoreleasetheload, inadditiontohavingahighfuelweightonboardandpossiblybeinginahostilemountainenvironment.

1.9.2. Landing point

IntheSpecialOperationsManual,Firefighting(MOE-LCI),point2.2.1statesthefollowingregardingthelandingpoint:

Landing spot

The landingspot foraFFflightmustbesufficientlywideandproperly free fromobstacles.Forreferencepurposes,anareathat istwicethediameteroftherotorcanbeconsideredtobesufficientlywide.

As for the factors tobeused to select the landing spot from theair, it providesthefollowinginstructions:

The landing spot for dropping off or picking up firefighters must be carefullystudied.TothisendthePIC(Pilot incommand)mustkeepinmind:

Selecting the landing spot

• Flyaroundthechosenspot:

— Ahigh reconnaissance run,above300ft, toevaluate theareasurroundingthespot,


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— A low reconnaissance run, above 100 ft, to check for obstacles on theselectedapproachanddeparturepaths,and

— A final reconnaissance run while on slow approach, >60 kts, to check theground.

• winddirectionandspeed• elevationofthelandingspot• nearbyobstacles• approachanddeparturepaths• helicopterweightandreservepower• conditionandgradientofterrain• proximityofoperationalareaandeaseofaccessforfirefighters.

Factors that determine the landing spot selected from the ground

IfthemembersoftheFFsquadareonthegroundandarerequestingtobepickedupbytheh/c,thefollowingpointsaretobeconsideredwhenselectingthelandingspottobepickedup:

During the landing

Standinviewofthepilot, infrontofthehelicopterandleavingthelandingspotclear.Be particularly careful with the rotors, especially the tail rotor which, given itsspeed,maynotbevisible.Donotapproachthehelicopterwithoutbeinginstructedtodosobythecrewanddonotgiveanyunnecessarysignals.

1.10. Additional information

1.10.1. Training the aircraft operator is required to give squad members

Theaircraftoperatorhasaworkplacehealthandsafetymanagementsystem inplace,aspartofwhichithasconductedastudytoevaluatetheoccupationalhazardsinherentto helicopter operations. This study includes the work done by third parties with theoperator’saerialassets.

As for the personnel who comprise the usual crew of a helicopter (e.g. air-droppedfirefightingsquads,medicalpersonnel,rescuepersonnel,etc.),thisdocumentstatesthattheywillbeinformedofthehelicopter’ssafetyandemergencysystemsingeneral,andoftheuseandoperationofthosesystemsonthespecificmodelofhelicopterinwhichtheywillbeflying.This informationandtrainingwill include:


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• Identification of every helicopter access door, both in the cockpit and in thepassenger/cargocompartments.

• Normalopeningandclosingoperationsofeveryhelicopteraccessdoor,bothinthecockpitandinthepassenger/cargocompartments.

• Identification,locationandoperationoftheportablefireextinguishersinsidethehelicopter.

• Identification, locationandoperationofeveryemergencyexit inthehelicopter,includingemergencyreleasesondoorsorwindows.

• Identificationanduseofthevariousrestraintsystems(seatbelts)inthehelicopter.• Locationandactivationoftheemergencybeacon(ELT), ifapplicable.• Locationandactivationoftheemergencyfuelcut-offsystems,ifapplicable.• Location and activation of the emergency electrical shut-down systems, if

applicable.

As for “Safety when deploying and/or stowing the BAMBI BUCKET”, it provides thefollowinginstructions:

Everyhelicoptermodelhasorusesdifferentcarryingsystemsandprocedures formaneuverswiththeBambibucket.Asaresult,air-droppedfirefightingcrewsmustbeinstructedandtrainedonthemodelbeingusedatanygiventime.

If a different helicopter model is used for any reason, the members of the air-droppedfirefightingcrewsmustbetrainedonthenewmodelandinitsassociatedprocedures.

Themaneuversinvolvingtheremoval,deployment,retraction,foldingandstowingof the Bambi bucket in its carrying basket are to be carried out by members oftheair-droppedfirefightingsquad.

Thesepersonnelshallbedesignatedasthepermanentandusualhandlersof theBambi bucket. Only in their absence, medical leave or any other unforeseencircumstancecananotherdesignatedcrewmemberhandlethistask.

Even though the samedesignatedpersonnelwillhandle theBambibucketduringan operation, EVERY member of the air-dropped firefighting brigade shall beinstructedandtrainedonthemaneuversandproceduresassociatedwithit,suchas:

• Stowinganddeployingit• Loadingandunloading• Securing• Latchingandunlatchingtheloadhook(ifapplicable)• Electricalconnection(ifapplicable)• Procedureforcheckingthewaterreleasesystem• Identifyingandsolvingtypicalmalfunctionsorproblems.


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Theymust also receive trainingon the various components andelementsof theBambi bucket and be able to determine its condition and ensure its safe andproperoperation.

Periodichands-on trainingwillalsobeheldat thepilot’sdiscretion,orweeklyataminimum if therearenoflightsor serviceswhere this trainingwasconducted.The leaderofeachsquadmustkeepa record foreachcrewmemberassigned tohandletheBambibucketofallthetrainingcarriedoutbyeachoneandthedateofthetraining.

Duringoperations,allmaneuversaretobesupervisedbytheleaderorforemanoftheair-droppedfirefighters,whowill relayallmaneuverstothepilotflyingeithervisuallyorviaradio.

1.10.2. Training received by firefighting squad

On31Mayand12June,theaccidentpilotgaveinitialandrefreshertrainingatthebasein Valencia de Alcántara on safety and emergencies to the various members of thefirefightingsquads, includingthefourmemberswhocomprisedthesquadassignedtothehelicopteronthedayoftheaccident.Thistrainingcovered:

• Generalsafetyregulationsontheground.• Generalsafetyregulationsintheair.• Safetyregulationsforpersonneltransportedbyhelicopter:

— Helicoptersafetyandemergencysystems. — Safetywhileboarding. — In-flightsafety. — Safetywhiledisembarking. — Safetyduringtakeoffand/orstowingtheBambibucket.

• Stepstotakeinanemergency:

— Emergencydescent. — Braceposition. — Exitingthehelicopter. — Smokeinthecabin. — Fireinthecabin. — Fireorexplosionafter impact.

• Flightpractice.• Otheractions:waterimpact,stepstotake.


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TheyalsoattendedtothefollowingformationsessionsandtrainingwithhelicoptersBell407andAirbusHelicoptersAS-350-B3:

• 21Maywithsquad“AireA”,Bell407andpilotdifferentfromtheaccidentone.• 21Maywithsquad“AireB”,Bell407andpilotdifferentfromtheaccidentone.• 4Junewithsquad“AireA”,EurocopterAS-350-B3.• 5Junewithsquad“AireB”,EurocopterAS-350-B3.• 5Junewithsquad“AireA”,EurocopterAS-350-B3.• 6Junewithsquad“AireB”,EurocopterAS-350-B3.• 11Juneconsquad“AireB”,EurocopterAS-350-B3• 22 July with squad “Aire A”, Eurocopter AS-350-B3 and pilot different from the

accidentone.• 22 July with squad “Aire B”, Eurocopter AS-350-B3 and pilot different from the

accidentone.

In addition, all crewmembers had received specific training on extinguishing fires andonpreventingassociatedoccupationalhazards.

1.10.3. Evaluation of the Bambi bucket opening test

Theinvestigationintotheaccidentrevealedacertaindifferenceofopinionamongpilotsregarding theneed todo theopening teston theBambibucketwhen it is takenoutofitsbasket,tothepointwheresomepilotsdidnotcarryoutthistest.

In lightof this the investigation teamdecided itwouldbe interesting toascertain theopinionofpilotsasawholeonthisissue,towhichenditrecommendedtotheoperatorthat it survey its pilots in an effort to gather their opinions regarding the test of theopeningsystemforthebucket.

Inaerpickedagroupofhighlyexperiencedfirefightinginstructorsandpilotsandaskedfortheiropiniononthesubject.

It should be noted that there are several different cases depending on the helicoptermodel inquestion,thoughtheycanbegroupedintothefollowingtwomaingroups:

• Bambibucket transported inanexternalbasketandalwaysconnected,both to theloadhookandtheelectricalcontrolsystem.

• Bambi bucket transported in the helicopter’s luggage compartment and physicallydisconnected.

Theproceduresusedbytheoperatoratthetimeoftheaccident,whichinvolvecheckingthe operation of the opening system, were the same for every helicopter type andrequiredthreechecks:


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• Pre-flighttest.Donebythepilotandamechanicbeforetheflight.• Testbythesquad.Donebythepilotandthesquadeverytimethebucketisdeployed.

Thiswasthetestbeingdonewhentheaccidenttookplace.• Over-watertest.Donebythepilotbeforestartingthewaterdrops.

The replies receivedwere fairlyconsistent.Theanalysisof thecurrentsituationand itspros and cons was based on the risk/reward ratio, with the pre-flight and over-watertestsbeingregardedasunquestionablybeneficial ineveryscenario.

The test by the squad, however, was mostly viewed as dangerous, since it requiredhaving a squad member very close to the helicopter, which increased the risk of anaccident.

Asforthepros,therewereratherfewinthecasesofthebuckettypethatdoesnothavetobedisconnected inorder tobe stowed, since its connectionswouldnothavebeenmanipulatedafterthe lastpre-flightcheck,whichmakes it improbablethattheywouldhave been altered in the meantime. The test itself also has few benefits since thepossibilityremainsthatadisconnectionmayoccurontakeoffthatwilldisabletheopeningmechanism,anoccurrencethatwouldbedetectedbythepilotduringthewatertest.

Incontrast,thegeneralopinionwasthatbucketsthataredisconnectedwhentheyarestowed shouldbe tested, since their connections are alteredandneed tobe checkedbeforebeingused.

In light of this, theoperator decided to change its procedures anddo awaywith thebucketopeningtestdonebysquadsforbucketswhoseconnectionsarenotaffectedbythestowing/unstowingprocess.

This informationhasalreadybeenconveyedtoall instructorssotheycanstartpassingiton to thecrews.Therearealsoplans to informcrewsof thisduring theworkshopsthatareheldbeforethestartofthefirefightingseason.

Theoperator is alsopreparingfiveoperatingprocedures,one for eachaircraftmodel,containinginstructionsforoperatingwiththeBambibucket.Theseareexpectedtobedistributedbefore the start of the summer campaignandwill include the instructionsfortestingthebucket.

2. ANALYSIS

2.1. Communications

Whilethecommunicationsbetweenthepilotandfirecoordinatorwereeffective,thosebetweenthepilotandthesquadleaderdidnotappeartobe,sincetwosquadmembersboardedthehelicopterbelievingtheywerereturningtobase.


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2.2. Landing spot

Accordingtohisstatement,thepilotdidnotdothehighandlowreconnaissanceruns,instead flying over the road before landing directly. He was cognizant of the landingarea’s limitedsize.

The dimensions of the area where he landed are well below the two-rotor diameterlimitregardedastheminimumintheMOE.Infact,whenthehelicopterlanded,theaftpartofthetailconewashangingovertheinclinethatseparatedthetworoads.

Due to the limited area, the squad members were not able to stand in front of thehelicopter,havingtodosototheleftofthehelicopterinstead,nexttosomeroadsigns.

2.3. Actions of the squad

Sincetheareawherethesquadhadbeenoperatingwassouthoftheplacewherethehelicopterhadlanded,itsmembershadtogainaccesstothelandingspotfromtheleftofthehelicopter,whichisontheoppositesideofwherethepilotsitsinthehelicopter.

The squad leader placed himself in front of the helicopter and once received theclearancefromthepilottocomeclosertothehelicopter,hetransmittedthisinformationtotherestofthesquad.Possiblydueaprobleminthelastcommunicationheldbetweenthe pilot and the squad leader, the latter did not understand that the squad had tocontinue with the fire extinguishing operations and thought that they were going toreturn to the base. As a consequence the members of the squad approached thehelicopterandproceededtopackthetoolsandgetonboard insteadofextractingthebambibucketasthepilotwasexpecting.

When the statements fromtheothermembersof the squadwere reviewed,acertaindisagreementwasobserved in twoof them regarding thenumberofpeople involvedinunstowingtheBambibucket.Squadmemberno.1saidthatthreepeople(includinghimself) did it, while no. 4 said that this task was accomplished by him and anothercolleague.

As for no. 3, though he did not specify a number, he did state that he took part inunstowingthebucket.

The minimum number of firefighters required to unstow a bucket depends on theweightoftheequipment,thoughnormally it isbetweentwoandthree.

In the three statements there is one piece of information that can shed light on thisissue:eachindividualstatesthathetookpart intheactivity.


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Since information regarding one’s own involvement is more reliable than informationgivenabout someoneelse, itmaybeconcluded that, inall likelihood, threemembersofthesquadwereinvolvedinunstowingandlayingouttheBambibucket.

2.4. Test of the opening system on the Bambi bucket

Duetotheuncertaintyregardingtherisk/rewardratio involved incarryingoutthetestoftheopeningsystemonthebucket,theoperatorsurveyedsomeofitspersonnel.

This survey revealed that in helicopters where the bucket opening system is notdisconnected,it isnotnecessarytocarryoutthistesteverytimeit isunfolded.

Theoperatorisdisseminatingthisinformationtoitscrewsthroughtheworkshopsthatareheldbeforethefirefightingseasonstarts.Itisalsopreparingwrittenproceduresforthe different models it uses that it plans to have distributed to its crews before thesummercampaign.

ThisCommissionbelieves thatomitting the testof theopening systemon thebucketinthosemodelswherethefolding/unfoldingtaskdoesnotrequirechanginganyof itsconnectionswillmakefirefightingoperations saferbyminimizing theexposureof thesquadmembers.

Inapositivelight,theoperator’sresponsetothisissueisalsoworthnoting.Itconductedasurveyofasignificantsample,bothinqualitativeandquantitativeterms,ofitscrewsanddrewconclusionsthathaveresultedinchangestoitsprocedures,changesthathavebeenimplementedwithoutdelay.

2.5. Analysis of the initial loss of control of the aircraft

Theaccidentsequencebeganwhentheaircraftstartedtomoveuncontrollably.

Groundresonanceoroscillationisaphenomenonthatoccurswhenthemainrotorfirstdragvibrationmodeapproachesthenaturalrollfrequencyoftheaircraft.

The followingfigureprovidesabasicdiagramof theground resonancephenomenon,whichshowsthemarginthatexistsbetweenthecurvesinnormalconditions.Whenthemargindropstozero,thetwocurvescrossandresonancecanappear.

Thereareseveralfactorsthatcanaffectthisdiagram,andthusalterthepositionofthecurves:achangeinthespeedofthemainrotor(increase),avariationinthemainrotorhead’sstiffnesscharacteristics,achangeintheaircraft’snaturalvibrationfrequency,etc.


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Figure 7. Basicgroundresonancegraph

Increasingthespeedofthemainrotor,whichwouldshiftthebluelineinthegraphtothe right, can result froman inputmadeby thepilot to the fuel control (notpossibleonthemodel inthisaccident)orfromaproblemwiththegovernor,forexample.

The stiffnessof the rotorhead canbemodifiedby changes to the characteristicsofthefrequencydampers,forexample,andwouldresultinanupwardshiftofthegreenline.

Theaircraft’snaturalvibrationfrequencycanbeaffectedbyanyofthefollowingfactors:

• Aircraftweight• Statusofthelandinggear• Statusofthelandinggeardampers• Characteristicsoftheground

The following graph shows the effect of changing (lowering) the aircraft’s naturalvibrationfrequency.Theredcirclemarksthepointatwhichthetwolinesintersectandtheresonancecanbegin.

TheinformationrecordedontheDECUandVEMDindicatesthattherewasnosignificantchangetotherotationspeedofthemainrotor.

Thepotentiometeronthecollectivepitchanticipatorfailswhenthemeasurementofthepotentiometer’s relative position reaches the minimum (5%) or maximum (95%)thresholds, or when it varies at a rate in excess of 350% per second. The system’sdesign mechanically impedes these thresholds from being reached unless the sensorfails.


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Figure 8. Effectofvaryingtheaircraft’snaturalvibrationfrequencyonthebasicgroundresonancegraph

TheDECUusesthepotentiometer’spositiontodeterminethethrustthatisgoingtobedemandedatanygivenmomentbeforesaiddemandoccurs.Thisreadiestheenginetosupply thethrust that isdemanded,whichallows it tokeeptherotor’s rotationspeedwithinitsacceptablerange.

BasedonBEA’s,AirbusHelicopters’andTurbomeca’sexperience,afaultintheanticipatorpotentiometer is usually apartof the fault sequence that is recordedafter an impactwiththeground.Theremainingfaultsrecordedarealsoregardedasprobablyresultingfromtheimpactwiththeground.

The informationpresented above rulesout thepossibility that the rotational speedofthemainrotormayhavechanged,andthusthatthebluecurveinthegraphshifted.

The inspections of the main rotor head and of the gearbox suspension (see Section1.6.3)didnotrevealanyabnormalconditionsnorevidenceofanypre-existingfaultsordamage. Consequently, no significant changes affecting the main rotor head or thegearboxtransmissionarethoughttohaveoccurred,andthusthestiffnesscharacteristicsofthemainrotorheadremainedunaltered.

Theweightof theaircraftwaswithin limits,and thus isnotbelieved tohavehadanyeffectontheaccident.

Theconditionofthelandinggearwasacceptable.Onlythespringattheaftendoftheleft skidwasslightlyoutof specification, though it is thought that itwasbentduringtheaccident.


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Thedampersonthe landinggearwere ingoodconditionandthetestsperformedonthemindicatedthattheywereoperatingcorrectly.Thus,theyarenotbelievedtohaveplayedanyroleintheaccident.

Themarksfoundontheasphaltallowedinvestigatorstodeterminewherethehelicopter’sskidswereresting.Therightskidwasrestingentirelyonthepavedarea,whiletheleftwaspartiallyontheasphalt,itsfrontpartrestingontheasphaltwhiletherearpartwasonthedirt.Duetothegradientsofthetwoareaswheretheskidwasresting,only itsendswerebeingsupported.Thesectioninthemiddlewasleftsuspended.Itshouldalsobenotedthattheweightontherearpartoftheskidwasonlybeingsupportedbythespring,whichisahighlyelasticcomponent.

Whenthepilotcheckedthatthehelicopterwasproperlysupportedbymovingthecycliclever slightlyaround theneutralpoint, thehelicopterdidnotmove,probablybecauseitspositiononthegroundwassolidenoughtogivetheappearanceofbeingstable.

Otherfactorsthatcouldhaveaffecteditsstability,suchasthepositionsofthecollectiveandcycliccontrols,shouldalsobetakenintoaccount.

After landing, the pilot must fully lower the collective pitch lever and keep it in thatposition.

The pilot must move the cyclic control lever into a position where he feels that thestabilityandvibrationconditionsareadequate,andthenkeepitthere.

Aswasnoted inSection1.6.2,thefrictiononboth leverswasat itsminimumsetting.Under these conditions, the resistanceoffered toanymovement is very low,meaningthatthepilotmaymakeaninvoluntaryinputtothecontrolsthatheisunawareof.

After landing, the pilot had to wait for the squad members to arrive. Once they did,twoofthemclimbedonboardthehelicopter,whichforcedthepilottoturnaroundtoinformthemthattheyhadtoexittheaircraftandunfoldtheBambibucket.Oncethisoperationwascomplete,heturnedhisattentiontotestingthebucket,atwhichpointoneof thefirefighterswentunderneath thehelicopter topull on the cable. Itwasatthatmomentthatthehelicopterbegantomove.

Severalminuteselapsedbetweenthe landingandthetimethehelicopterwentoutofcontrol.Duringthistimethepilothadtomove,turnaround,giveinstructions,diverthisattention,etc.Inshort,itseemslikelythattheseactions,alongwiththelongstretchoftime that the helicopter remained on the ground, could have resulted in the pilot’sprovidinginvoluntaryinputstothecontrollevers,inputsthatcouldhavegoneunnoticeddue to theminimal resistanceofferedby the levers.Alsoduring this time, thebucketwasremovedfromitsbasket,whichalteredtheaircraft’sweightandthepositionofitscenterofgravity.


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Anymovementsoftheleverscouldhaveresultedinasubstantialshiftinthehelicopter’sequilibriumconditions.Movingthecollectiveupwouldhaveincreasedtheliftprovidedby the main rotor, which would imply an equal drop in the weight supported by theskids,leavingthehelicopterinaconditioncommonlyknownas“lightonitsskids”.Anyshift inthecyclic lever’sposition, incontrast,wouldresultachangeindirectionoftheliftvector.

Asfortherestingposition,itshouldbenotedthattheleftskidwasonlyrestingonitsends, the front one on the asphalt and the rear one on the dirt. The rear one, inaddition, was resting on the tip of the spring, which is a highly elastic component.Under theseconditions, thesupportprovidedby theskid isnotatall soliddueto theelasticityofthespring.

This could have affected the aircraft’s natural frequency vibration curve, causing it toshiftdownward(seeFigure8),withtheensuingreduction inthemarginofseparationbetweenthecurves.

ThesecouldhavebeentheconditionspresentwhenthetestoftheBambibucketwasbeingcarriedout.Itislikelythatoverthecourseofthetest,thepilotcouldhavemovedoneofthecontrolleversinadvertently,andthatthatmotionofthecontrolscouldhavebeenenoughtonegateanyseparationinthecurvesandstarttodestabilizetheaircraft.

2.6. Analysis of the wreckage and marks on the ground

The marks left on the ground and the positions of the debris were used to try todetermine the aircraft’s positionwhen thepilot lost control, aswell as its subsequentmotionandanyimpacts.

Thetwoparallelmarksfoundontheasphaltwereintheareawhere,accordingtotheeyewitnesses, the aircraft landed. It was oriented toward 265°, which matches thecoursethepilotsaidhetook.Also,thedistancebetweenthetwomarks,alittleover2m, ispractically thesameas thatbetweenthehelicopter’sskids. Itmaybeconcluded,then,thatthesemarkswereleftbythehelicopter’sskidsandindicatethepointwhereit landed.

Behindthemarkleftbytherightskidwasanothermark,elliptical inshape(seeFigure4),nexttowhichwasfoundthepartoftherightskidthatbrokeoff,aswellastherearcrossbarfromthelandinggear.Thismarkwasleftmainlybythepartthatbrokeofftherearcrossbar.

The preceding findings and the eyewitness statements indicate that the helicopterstartedmovingslightlyforwardandthenbackward,leavingthefaintmarksmentionedearlier,beforerisingofftheground.


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Itmusthavebeeninthesefirstfewinstantswhenthefirefighterwhowasgoingtodothe opening test on the Bambi bucket grabbed the right skid. The helicopter wasswayingbackandforth justoff thegroundwith thefirefighterhangingonto theskidforsometime.Whenhereleasedtheskidtogetaway,therewasanabruptchangeinthe forces acting on the aircraft. This caused the tail to descend suddenly, making itpossibleforthetailrotortoimpactagainsttheedgeofthegradient,breakingitsbladesandcausingtherotortodetach.

Boththeskidandthetailguardatthebottomaftendofthefuselagearedesignedtokeepthetailandthebladesontheanti-torquerotorfromstrikingtheground.Despitethis, inthisaccidentthebladesontheanti-torquerotordidstriketheground.

Ananalysisofthegeometryofthehelicoptertailandthefeaturesoftheaccidentsiterevealedthat itwaspossible for thetail rotorbladestoreachthegroundwithoutthisbeingpreventedbythetailskidorthetailguard.Thiswaspossiblewiththehelicopterfacingsouthwestandthetailovertheincline.

Itwaspreciselysomeofthesedetachedfragmentsofthetailrotorbladesthatimpactedthebackofthefirefighterwhohadbeenunderneaththehelicopterashetriedtogetaway.

Afterlosingthetailrotor,thehelicopteryawedsharplytotheleft,whichworsenedtheaircraft’s lossofcontrol.

Atsomepointduringthisturnthehelicopterfellonitsrightskid,causingittobreak.

The tail guard broke when it impacted against the edge of the incline during thehelicopter’sfirst rotation, though it couldnotbedeterminedwhether thisoccurredatthestartorendoftherotation.

The helicopter continued rotating to the left, resting on the broken end of the rearcrossbarandonthetailskid,whichleftafaintmarkontheasphaltedarea.Aftermakingpracticallyoneentirerotationinthisposition,theaircraftturnedoveronitsrightside.

Itwasas itfelloverthatthemainrotorblades impactedtheground,causingthemtobreakanddetach.

After falling on its side, the helicopter came to rest on the parts of the blades thatremainedattachedtothemainrotor,ontheendoftherearcrossbarandontherighthorizontalstabilizer.

Sincethemainrotorwasstillturningunderpoweratthistime,onstrikingthegrounditgrippedit,asaresultofwhichthehelicopterstartedturningcounterclockwiseasseenfromabove,makingacompleteturnthatleftthecircularmarkmadebytheendoftherighthorizontalstabilizer.


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2.7. Pilot’s actions. Friction setting

In its Flight Manual the helicopter manufacturer underscores the need to adjust thefriction settings on the cyclic and collective levers during the various phases of flight,notingthattheseneedtobeadjustedtoprovidethepilotwithafeelforthemovementoftheseflightcontrols.

The friction settingmodulates the controls’ resistance tomovement, helping thepilotfeel the inputshe isprovidingwhileoffering referencepointson theamountof inputbeingapplied.Theresistancetomotionofferedbythefrictionalsomakesitsothatanyinadvertentmovementofthecontrolsbythepilotdoesnotgounnoticed.

Inaddition,afterlandingandoncethecontrolsareputinaneutralposition,thefrictionkeepsthemfrommovingbythemselves,asmighthappenifthepilothastoreleaseoneofthem,suchastosignalpersonneloutsidethehelicopterwhoareawaitinginstructions.

It is well-known that having little resistance to movement in the control levers favorsover-control, something that is particularly relevantwhen thepilot reacts suddenly, asmightbethecasewhenrespondingtosomeabnormalsituation. Incontrast,therightamountoffrictionprovidesanartificialsenseoftherangeofmotion,making iteasiertomovetheleversjustthedesiredamount,andthustocontrolthehelicopter.

In the accident analyzedherein, once thehelicopterbecameunstable, thepilot actedtoregaincontrolbutwasunabletodoso,possiblyduetothreecircumstances:

• Limiteddimensionsof the landingarea. Thepresenceofobstacles aroundmuchoftheperimeterofthelandingareahandicappedthepilot,forcinghimtoimmediatelycorrectanymovementtowardsaidobstacles.

• The lackof friction in thecontrols,whichmade iteasier for thepilot toovercorrectfortheaircraft’smovements.

• Thefirefighterholdingontotherightskid,whichdoublyhamperedthemaneuvers:bylimitingtheactionsofthepilotwho,knowinghewasunderneaththehelicopter,was afraid of injuring him; and by the variable loads on the aircraft caused by thefirefighter.

3. CONCLUSIONS

3.1. Findings

• The pilot had the license and ratings required for the firefighting tasks he wasengagedin.

• The aircraft had valid documentation and had been maintained in keeping with itsmaintenanceprogram.


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• Communicationsbetweenthepilotandthesquadleaderwerenotfullyeffective.• Thechoiceof landingspotdidnot fullyadhere to the instructionscontained in the

operator’sSpecialOperationsManual.• Thedimensionsofthelandingareawerebelowtheminimumsrecommendedbythe

operatorinitsOperationsManual.• Theaircraft landedwiththe leftskidpartiallyrestingontheasphaltandpartiallyon

dirt,andwiththeaftmostpartofthetailovertheinclinebetweenthetworoads.• WhilecarryingoutthetestoftheopeningsystemontheBambibucket,theaircraft

destabilized.• Noevidencewasfoundofanypre-existingfaultormalfunctioninanyaircraftsystem.• Thedestabilizationprobablyoccurredasaresultofthecharacteristicsoftheground

onwhichtheskidswereresting,andofsomeinvoluntarymovementofthecyclicandcollectivecontrols

• Thefrictiononthecyclicandcollectivecontrolswasat itsminimumsetting.• While trying to control the aircraft’s movements, the pilot likely provided excessive

inputstothecontrol levers.• ThefirefighterwhowastestingtheBambibucketheldontothehelicopter’srightskid

whenitbecameunstable.• Theanti-torquerotorstrucktheedgeoftheincline,causingitsdetachmentandthe

total lossofcontroloftheaircraft.

3.2. Causes

This accident resulted from a lack of compliance with the landing procedures, whichcausedthehelicoptertobecomeunstablewhileontheground.Thisdestabilizationwasprobably due to the uneven support provided by the skids and to an involuntarymovementofthehelicopter’scontrol levers.

Contributingtothisaccidentwere:

• Thereduceddimensionsofthelandingarea.• TheperformanceofthetestontheBambibucket’sopeningsystem.• Thefrictionsettingonthecyclicandcollectivecontrol levers.• Thevariableloadsassociatedwiththeworkerhangingfromtheskid.

Documents

DATA SUMMARY - Ministerio de Fomento · main rotor and the right horizontal stabilizer. There was a significant deformation on the stabilizer where it was supporting the weight of