AIRCRAFT ACCIDENT REPORT 1/96
ACCIDENTS INVESTIGATION DIVISION
CIVIL AVIATION DEPARTMENTHONG KONG
Report on the accident toAerospatiale SA315B Lama VR-HJG8 km west of Hong Kong Sek Kong Airfieldon 29 June 1995
HKP363.124H7B96
HONG KONG GOVERNMENT
THE UNIVERSITY OF HONG KONGLIBRARIES
Hong Kong Collection
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OUR REF:
YOURREF:
TEL NO.
CABLES: AIRCIVIL HONGKONG
TELEX: 61361 CAD HK
CIVIL AVIATION DEPARTMENT46th floor,
Queensway Government Offices,66, Queensway,
Hong Kong.
His Excellency the Governor, Hong KongGovernment HouseHong Kong
Sir,
I have the honour to submit the report by Mr. K.F. Cheung, an Inspector ofAccidents, on the circumstances of the accident to Aerospatiale SA315B, VR-HJG, whichoccurred in Hong Kong on 29 June 1995.
I have the honour to beSir,
Your Excellency's obedient servant
R. A. SiegelDirector of Civil Aviation
BIB.REG.NO.
DATERHTD 2 4 JAN
CLASS NO.
AUTHOR NO.
REBOUND
ContentsPage
SYNOPSIS i
1. FACTUAL INFORMATION
1.1 History of the flight 21.2 Injuries to persons 31.3 Damage to aircraft 31.4 Other damage 31.5 Personnel information 31.6 Aircraft information 51.7 Meteorological information 71.8 Aids to navigation 71.9 Communications 71.10 Aerodrome information 71.11 Flight recorders 71.12 Wreckage and impact information 71.13 Medical and pathological information 81.14 Fire 81.15 Survival aspects 81.16 Tests and research 81.17 Organizational and management information 81.18 Additional information 91.19 Useful or effective investigation techniques 12
2. ANALYSIS
2.1 General 132.2 The recognition of working procedures 132.3 Certification of work accomplishment 132.4 The installation of the secondary retention device 14
3. CONCLUSIONS
3.1 Findings 153.2 Causes 16
4. SAFETY RECOMMENDATIONS 17
5. APPENDICES
Tail rotor head pitch change mechanism Appendix 1Secondary retention device on pitch change mechanism Appendix 2Wreckage plot Appendix 3Photographs of aircraft wreckage Appendix 4
ACCIDENT REPORT SA315B REG. VR-HJG
Owner and operator:
Aircraft Type and Model:
Nationality:
Registration:
Place of accident:
Date and Time:
Heliservices ( Hong Kong ) Limited
Aerospatiale SA315B Lama ( Helicopter)
British ( Hong Kong )
VR-HJG
Tan Kwai Tsuen Quarry, New Territories, Hong KongLatitude: 22° 25'43.7" NLongitude: 114° 00'0.7" E
29 June 1995 at 0910 hours (0110 hours UTC)
(All times in this report are local except as stated.Hong Kong standard time is UTC plus 8 hours)
SYNOPSISThe accident was notified to the Accidents Investigation Division of the Civil AviationDepartment (CAD) by the operator on the morning of the 29 June 1995. The investigation by ateam of CAD Inspectors of Accidents commenced on the same day.
The aircraft departed the operator's base at Sek Kong airfield at approximately 0830 hours(0030 hours UTC) on 29 June 1995 to carry out underslung load operations in support of theerection of electricity pylons in the New Territories. The operation was in accordance withvisual flight rules (VFR) in uncontrolled airspace. At 0910 hours (0110 hours UTC) the pilotmade an approach to a work site at Tan Kwai Tsuen Quarry to collect a further load.Approaching the site into wind, the pilot lowered the bucket to the ground and appliedcollective pitch to stabilise in the hover. The aircraft started to develop a yaw to the left whichdid not respond to the right hand pedal input applied by the pilot. While positioning the aircraftaway from workmen on the ground the yaw developed into an uncontrollable spin to the left.The pilot carried out an emergency landing from 100 feet during which the aircraft rolled overonto its side and sustained major damage. There were no injuries to the pilot or persons on theground.
The investigation identified that the loss of yaw control was due to the tail rotor gearbox pitchchange rod becoming detached from the mechanism which adjusts the pitch of the tail rotorblades in response to control pedal inputs. The pitch change rod became detached from thepitch change mechanism following the loss of the single attachment bolt in flight. This in turnwas due to a cotter pin and a secondary retention device not being reinstalled in accordancewith the requirements of the maintenance manual during maintenance carried out on the aircraftprior to the accident flight.
I. FACTUAL INFORMATION
1.1 History of the flight
During the afternoon prior to the day of the accident the aircraft was positioned tothe operator's hangar at Sek Kong airfield to enable a routine 100 hour inspection tobe carried out. The afternoon duty engineer carried out maintenance on this aircraftand then went off shift at approximately 2000 hours (1200 hours UTC). Thefollowing morning the duty engineer arrived at approximately 0720 hours (2320hours UTC on the 28 June 1995) and carried out a duplicate inspection on theaircraft which was the only recorded uncompleted item of maintenance from theprevious afternoon. After this the aircraft was released for service for the day'sflying program.
The aircraft was due to carry out a number of flights which involved underslungload operations transporting concrete for the erection of power line towers. Thepilot arrived at the operator's base at around 0730 hours (2330 hours UTC on the 28June 1995). He commenced his first flight at approximately 0830 hours (0030 hoursUTC) and had delivered several buckets of concrete at a site near Tai Lam Gap. Hethen flew back to the base at Sek Kong to replace the underslung load chain with ashorter 30 foot chain. An empty concrete bucket was hooked up and the aircraftflew to a concrete pick up point coded BS38(H) in Tan Kwai Tsuen Quarry, whichwas the site of the accident.
The aircraft arrived at BS38(H) and flared into a hover. As the pilot lowered thebucket to the ground and applied collective pitch the aircraft started to yaw to theleft. Directional control was applied to stop the yaw but there was no response evenwith full tail rotor pedal input. The pilot reported that he raised the collective pitchslightly to move the aircraft away from workmen on the ground below. At thispoint the aircraft started to spin to the left and became uncontrollable, the pilotimmediately closed the fuel shutoff cock, shutting down the engine, and proceededto carry out an emergency landing. The aircraft continued to spin and madeapproximately three turns before it impacted the ground where it rolled over andcame to rest on its right side. The pilot, who was uninjured, vacated the aircraft andreported the accident to his company.
The aircraft was examined at the accident site by inspectors from the AccidentsInvestigation Division of the Civil Aviation Department. A preliminary inspectionof the tail rotor pitch change mechanism revealed that the attachment bolt whichsecures the tail rotor pitch change spider to the tail rotor pitch change rod wasmissing.
1.2 Injuries to persons
Injuries
Fatal
Serious
Minor/None
Crew
0
0
1
Passengers
0
0
0
Others
0
0
0
1.3 Damage to aircraft
The aircraft suffered extensive damage in the ground impact but remained intact.The main rotor head, including all rotor blades, was destroyed. The tail boom wasseverely damaged with the centre frame slightly bent at one engine support tube.The tail rotor driveshaft was found to be buckled but there was no visible damage tothe tail rotor gearbox, hub and blades. The upper cabin assembly was severelydamaged and both the left and right longitudinal beams of the lower cabin assemblywere distorted. The right hand skid and the forward right hand skid leg weredamaged.
1.4 Other damage
No other damage was reported.
1.5 Personnel information
7.5.7 Pilot:
Licence:
Air craft ratings:
Last medical examination:
Last company base check:
Last company line check:
Male, aged 31 years
Commercial Pilot's Licence valid until24 July 2000
Aerospatiale SA315BEurocopter (France) AS355N
29 July 1994, Class 1, no limitations,valid until 30 July 1995
3 February 1995
2 May 1995
Flying experience: Total flying hours: 4,777.4 hoursTotal hours on type: 2,077.0 hoursHours in preceding 7 days: 24 hoursHours in preceding 28 days: 60 hoursRest period before duty onday of accident flight: 10 hours
1.5.2 Maintenance engineer(Afternoon shift on 28 June 1995local time)
Licence:
Type ratings held:
Experience:
Male aged 39 years
Hong Kong Aircraft MaintenanceEngineer's Licence valid until15 June 1996
Category A&C (Aircraft/Engines)Aerospatiale SA315B withArtouste IIIB.
Total experience:Type ratings held :
6 years7 months
1.5.3 Maintenance engineer(Morning shift on 29 June 1995local time)
Licence:
Type ratings held:
Experience:
Male aged 45 years
Hong Kong Aircraft MaintenanceEngineer's licence valid until16 February 1997.
Category A&C (Aircraft/Engines)Turbine Engined Gyroplanes/Helicopters Paragraph 7.3 (whichincludes SA315B)
Total experience:Type ratings held:
28 years17 years
1.5.4 Maintenance assistant
Licence:
Experience:
Male aged 34 years
None
5 years engaged in aircraft servicing.
1.6 Aircraft information
1.6.1 Leading particulars
Manufacturer:
Model:
Constructor's number:
Date of manufacture:
Certificate of Registration:
Certificate of Airworthiness:*
Certificate of Maintenance:
Total airframe hours:
Engine:
Maximum permissible weightwith external load:
Actual aircraft weight at timeof accident:
Maximum permissible under slungload:
Estimated weight of under slungload at the time of accident:
Estimated fuel remaining atthe time of the accident:
Aircraft centre of gravity at timeof accident:
Aerospatiale
SA315BLama
2601
June 1981
Registered in the name ofHeliservices (Hong Kong) Limited
Transport Category (Passenger), lastrenewed from 4 November 1994 andvalid until 3 November 1995
Valid until 6,609.4 Total Aircrafthours or 10 June 1996 whichever issooner
6,305.1 hours
Turbomeca Artouste IIIB
2,300 kg (5,070 Ib)
Unknown but did not exceed themaximum authorised weight
1,136 kg (2,500 Ib)
100 kg (220 Ib)
Unknown but the tank was notempty
In normal range
1.6.2 Flight characteristics
The following information from the aircraft flight manual is relevant.
" Tail rotor failure is indicated by a sudden and uncontrollable turn to the left. Therate of turn will be dependent on the amount of power that was applied, and theweight of the aircraft, at the time of the failure."
"OVER TERRAIN UNFAVOURABLE TO IMMEDIATE AUTOROTATIVELANDING
Reduce collective-pitch just sufficiently to achieve the best compromise between therate of rotation to the left, the flight path speed and the rate of descent.
In all cases, at the end of the landing approach, with full low collective-pitch, it isimperative to shut down the engine by closing the fuel shut-off cock, andaccomplish the flare-out, maintaining a constant height above the ground untilforward airspeed is zero.
Apply collective pitch as necessary upon touching the ground.
Note : If tail rotor failure occurs close to the ground (i.e. blades damaged byhitting an obstacle) full low collective-pitch must be applied, even if this isto cause a very hard landing, and shut down the engine by closing the fuelshut-off cock, and if possible before touching the ground."
/. 6.3 Aircraft flight controls
The aircraft flight controls on the Aerospatiale SA315B are conventional. The mainrotor blade pitch is controlled by the cyclic and collective controls. The pitch of thetail rotor is controlled by foot pedals. The tail rotor provides anti-torque correctionand heading control by varying the pitch of the tail rotor blades to counteract torquegenerated by the main rotor.
The tail rotor head is of the three hinged blade type which are connected by pitchchange links to a pitch change spider. The pitch change spider is in turn attached toa pitch change rod which is part of the tail rotor gearbox. Attachment is by a singlebolt with the nut secured by a cotter pin. The movement of the pitch change rodvaries with inputs from the pilot's pedals which are connected to the cable drum onthe tail rotor gearbox. The tail rotor head pitch change mechanism is shown atAppendix No. 1.
The single bolt attachment of the pitch change spider to the pitch change rod is avital point in that loss of the bolt results in loss of directional control of the aircraft.This was recognised by the aircraft manufacturer who issued a recommendedService Bulletin No. 65.24 on the 1 February 1977 to provide a secondary retentiondevice to prevent the loss of the bolt in the event of the nut becoming detached. Thesecondary retention device is a polyamid collar which is positioned on the shaft of
the pitch change rod and fits over the attachment bolt. See Appendix No. 2. ServiceBulletin.No. 65.24 was applicable to this aircraft and had been embodied.
1.7 Meteorological information
The accident happened in daylight and the weather conditions, as recalled by awitness stationed at the accident site, were considered to be good. He said it wassimilar to the weather conditions two hours later when he was interviewed at thesame location.
The observed weather conditions were : scattered cloud estimated 2000 feet;surface visibility greater than 10 kilometers; wind calm; with no precipitation.
1.8 Aids to Navigation
Not applicable.
1.9 Communications
The aircraft "HELI-JG" established radio communication with Sector InformationService provided by the Royal Air Force Air Traffic Control on 122.4 MHz at SekKong Airfield. The aircraft was airborne from the operator's base (in Sek Kong) at0838 hours (0038 hours UTC) and proceeded to Tai Lam Sector. At 0900 hours(0100 hours UTC) the aircraft checked operations normal with Sector InformationService which was acknowledged. . That was the last radiotelephony (RT)communication recorded on the tape. At 0930 hours (0130 hours UTC), a phonecall was received at Sek Kong Tower from the aircraft operator advising of theaircraft accident.
1.10 Aerodrome information
Not applicable.
1.11 Flight recorders
There was no requirement for a flight recorder to be installed and none was fitted onthis aircraft.
1.12 Wreckage and impact information
As recalled by the ground witness the aircraft spun about three turns before itimpacted the ground. The pilot stated that the aircraft hit the ground on its right
hand skid and then rolled over onto its right side. There were no apparent impactmarks but .this fact was supported as the aircraft right hand skid was found to beseverely distorted with the forward leg fractured and no damage was found on theleft hand skid.
The wreckage when inspected was resting on soft grass and was complete, nothaving broken up on impact. The most obvious damage was to the main rotor withall three blades destroyed and the right hand skid damaged as described above.Refer to Appendix No.3 and Appendix No.4.
1.13 Medical and pathological information
The pilot was medically examined shortly after the accident. It was concluded bythe medical officer that the pilot was fit at the time of the accident and there were norelevant medical factors relating to the reported events. Blood and urine sampleswere sent to the government forensic laboratory for alcohol and drug screening,there were no significant findings.
There were no other injuries.
1.14 Fire
There was no fire.
1.15 Survival Aspects
All the aircraft seats, including the seat belts, were found to be in good condition.There was no deformation evident even though the cabin assembly was damagedand distorted. The cabin door operated correctly and provided the pilot a viableescape path.
1.16 Test and Research
There were no specific tests or research carried out.
1.17 Organizational and management information
Heliservices (Hong Kong) Limited holds an Air Operators Certificate which enablesit to undertake flights for the purpose of public transport in accordance with theconditions specified in the certificate. Its maintenance organisation is approved inaccordance with the Air Navigation (Overseas Territories) Order 1977 and complieswith Hong Kong Aviation Requirements 145. The maintenance facility is managedby a Chief Engineer assisted by three licenced engineers.
1.18 Additional information
L18.1 Maintenance carried out immediately prior to the accident flight
The sequence of events are as recalled by the engineers during interviews carried outfollowing the accident.
Following completion of the day's flying on the 28 June 1995 the aircraft waspositioned to the operator's base at Sek Kong airfield where a 100 hour inspectionwas to be carried out. This was a routine inspection required by the ApprovedMaintenance Schedule CAD/MS/SA315B/HS4 Rev. O. To facilitate and assist theengineers carrying out inspections, the company print a routine worksheet from adatabase which lists the items to be accomplished.
The duty engineer who was to carry out the inspection was on the afternoon shiftfrom 1300 hours (0500 hours UTC) to 2000 hours (1200 hours UTC). The companyhad recently introduced a two shift system to meet operational needs.
The inspection on the aircraft commenced at approximately 1545 hours (0745 hoursUTC) and the engineer was assisted by a non-licenced maintenance assistant. Oneitem of the routine inspection required the three pitch change links, which connectthe pitch change spider to the tail rotor blades, be disconnected to complete a checkon the tail rotor blade hub bearings. When carrying out this check the engineernoted that a leather bellows, which is fitted over the tail rotor pitch change rod toprevent contamination of the tail rotor head, was in poor condition and decided toreplace it. The replacement of the bellows required the disconnection of the pitchchange spider from the pitch change rod. The engineer had carried out this task onmany occasions and as it was a simple task he did not make reference to the aircraftmaintenance manual. The required procedure for the disconnection of the pitchchange spider is described in the maintenance manual Chapter 56.20. Thereplacement of the bellows was not an item required by the Approved MaintenanceSchedule and was therefore not referenced on the routine worksheet. The companyprovides aircraft worksheets, reference HS/ENG/016, which are used to recorddefects, the work required and carried out additional to the routine inspection. Theaircraft worksheet also requires the certifying engineer to complete a Certificate ofCompliance for the work carried out. The engineer did. not raise an aircraftworksheet at the time he decided to replace the bellows.
When the bolt which secures the pitch change spider to the pitch change rod wasremoved the engineer saw that the shank was worn and he made a mental note tochange the bolt during re-assembly. The items removed, which comprised the bolt,castellated nut, cotter pin, secondary retention device and the worn bellows togetherwith its associated clamp were placed on a workstand adjacent to the aircraft. Atthis point in time the engineer stopped work on the tail rotor assembly to carry outan inspection on the engine at the request of another engineer who was on duty onthe morning of the 29 June 1995, the day of the accident. This engineer had come towork specifically to carry out an inspection on the engine to support a futureapplication for a life extension programme. After the inspection was completed thesecond engineer returned home. There was no record of this inspection recorded in
the aircraft documentation. After assisting with the engine inspection, the engineerdrained the tail rotor gearbox oil. Again this maintenance was not recorded in theaircraft documentation. He then fitted the new bellows onto the tail rotor pitchchange rod and using the old bolt re-aligned the pitch change spider onto the pitchchange rod. He installed the nut and tightened it up. At this point he rememberedthat he intended to change the bolt and did not proceed to insert the cotter pin tolock the castellated nut. He carried on and re-assembled the pitch change linksbetween the pitch change spider to the tail rotor blade sleeves. He recalled that hecompleted other maintenance activities in the vicinity of the tail rotor and then tooka break.
During this break, although the engineer noted that the maintenance assistant hadcleaned the area around the aircraft of the items used on the check, he was not awarethat the old bellows together with the secondary retention device, which he left onthe workstand, had been removed as well. On his return to the aircraft the engineerforgot about his intention to replace the bolt in the pitch change mechanism andwent on to complete other maintenance tasks on the aircraft.
The engineer then completed the aircraft check paperwork and signed all the entriesto signify the work had been completed. The last item on the routine checksheet is aduplicate inspection which the engineer signed for the first inspection. Theduplicate inspection statement, which is pre-printed on the routine worksheet, leavesa space where the engineer who has performed the disassembly of a control systemmust identify the items on the routine worksheet which are the subject of theduplicate inspection. The duplicate inspection requirements were not identified bythe engineer. The engineer subsequently raised an aircraft worksheet whichrecorded that the tail rotor bellows had been replaced and signed the Certificate ofCompliance. There was no mention on this worksheet that the pitch change spiderhad been disconnected from the pitch change rod and no duplicate inspection wascalled up. The engineer recalled that he placed the aircraft worksheet in the stores toalert the storeman that a bellows had been used and to re-order for stock. Theroutine worksheet was placed with the aircraft technical log for the attention of theduty engineer the next morning. The engineer considered the check and thepaperwork were complete at approximately 1845 hours (1045 hours UTC) followingwhich he went off shift.
On the morning of the 29 June 1995 the duty engineer arrived at approximately0720 hours (2320 hours UTC on the 28 June 1995). Prior to the aircraft departingfor the day's flying he reviewed the technical log and the check paperwork. He thenproceeded to carry out a duplicate inspection on the aircraft following which hesigned for the second inspection and the aircraft was then released for service. Theduplicate inspection he carried out comprised the tail rotor pitch change links forcorrect locking and assembly, flying controls for full, free and correct movement,and oil/fuel filters for security and locking. He did not recall carrying out a specificcheck of the pitch change spider to pitch change rod for correct assembly and alsodid not recall seeing the aircraft worksheet which recorded the replacement of thetail rotor bellows.
10
1.18.2 Findings at aircraft crash site
On being notified of the accident, the duty engineer attended the crash site where henoted the bolt which secures the tail rotor pitch change spider to the tail rotor pitchchange rod and the secondary retention device were missing. The secondaryretention device was later found at the operator's maintenance base.
1.18.3 Aircraft maintenance documentation
The company use a pre printed worksheet for the routine work requirementsrequired by the Approved Aircraft Maintenance Schedule and an aircraft worksheetto record any additional or non routine work carried out. An aircraft worksheetreference book is provided to record a sequential reference number for routine andnon routine worksheets used during aircraft maintenance. No references wereentered for this particular maintenance inspection on VR-HJG. There is noprovision on the routine worksheet to indicate or record if any non-routineworksheets have been raised and there was no tally sheet to record thedocumentation raised during a scheduled maintenance inspection.
A review of the routine worksheet for the 100 hour inspection revealed a number ofanomalies. The tasks are grouped together by subjects and systems. Thelubrication tasks were all pre fixed 05-00-302 however this did not align with themaintenance manual task reference. The second lubrication item also refers to a"tail rotor spin check for hard points" and "check pitch change links for play.Service letter 1051-05-91 refers." Therefore this item contained three separate tasksunder the heading of lubrication. The tail rotor spin check for hard points was thetask that required the disconnection of the tail rotor pitch links and this was the onlybreak down of the flying controls which required a duplicate inspection during the100 hour inspection. This task was derived from a manufacturer's service letter No599-65-84, however, this was not referred to on the routine worksheet. Wheninterviewing the engineers, it became apparent that the duplicate inspection calledup in the routine worksheet is considered to apply to more items than just the pitchchange links. The engineer who carries out the duplicate inspection also checks theflying control movement and certain oil and fuel filters for security and locking.These additional items are company requirements and are over and above theduplicate inspection required by the regulations and were not recorded individuallyon the aircraft routine worksheets.
Aircraft worksheets for recording non routine maintenance tasks require theengineer to enter the nature of the defect and the corrective actions carried out.When a task involves the disassembly of a flight or engine control system it isincumbent upon the engineer to record the requirement for a duplicate inspection tobe carried out following reassembly. To facilitate this, the company provide a stampwhich prints the duplicate inspection requirement.
11
1.18.4 Company procedures
A two shift system, mornings and afternoons, had been recently introduced by thecompany and there was a one hour overlap at the time of the afternoon shift changebut no overlap between the afternoon and morning shift. There was no formal shifthandover procedure in the Company Procedures manual.
The Company Procedures manual describes in general the aircraft documentationused by the company but did not specify the standard required for completion. Item5 of the general instructions in the Heliservices Approved Maintenance Schedulerequires duplicate inspections to be carried out on engine controls and flight controlsin accordance with British Civil Airworthiness Requirements whenever they aredisturbed. However, there were no further instructions on how they should becarried out and documented.
1.18.5 Engineering standards
The maintenance organisation is of a small size with 4 certifying engineers holdingtype rated licences. As type rated licenced engineers they are expected to work tohigh individual standards and the Company Procedures manual specifiedrequirements which had to be satisfied but did not define standards to be achieved,particularly in respect of the completion of aircraft documentation.
1.18.6 Corrective actions taken by the Maintenance Organisation
Immediate corrective actions were taken by the organisation. The more significantactions were:
The introduction of Engineering Notices, pending amendment of the CompanyProcedures manuals, to define standards for duplicate inspections anddocumentation, worksheet completion and the recording of documents used during amaintenance inspection.
The introduction of a shift handover procedure to ensure engineers are apprised ofwork carried out and any outstanding items.
A procedure was introduced to fix a readily visible flag to the area of the aircraftwhich requires the duplicate inspection.
1.19 Useful or effective investigation techniques
No special investigation techniques were used during the investigation of thisaccident.
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2. ANALYSIS
2.1 General
Examination of the wreckage confirmed that the bolt which secures the tail rotorpitch change mechanism to the tail rotor gearbox pitch change rod was missing.This resulted in the loss of directional control of the aircraft as the pilot controlinputs had no effect on the tail rotor blade pitch angle.
The aircraft was released for service following maintenance without a cotter pin tolock the castellated nut to the bolt securing the pitch change mechanism to the pitchchange rod. The secondary retention device for bolt retention was also not installed.During the forty minute flight prior to the accident it can be assumed that the nutvibrated off the bolt leading to the loss of the bolt and resulting in the loss ofdirectional control.
2.2 The recognition of working procedures
The task to disconnect the tail rotor pitch change mechanism to change the bellowsis not a complex task. However, the resulting accident serves as a reminder that nomatter how simple a task may be, if it is not carried out strictly in accordance withthe maintenance instructions it can have potentially catastrophic consequences. Thefact that critical tasks are not complex and are routinely carried out requiresvigilance and concentration at all times from individuals who carry them out.
2.3 Certification of work accomplishment
When a certifying engineer issues a Certificate of Compliance, all maintenancework carried out should be recorded. Prior to the granting of an AircraftMaintenance Engineer's Licence an applicant is examined on the requirements forthe certification of work accomplished on aircraft. This includes the requirementsfor duplicate inspections which are specified in detail in British Civil AirworthinessRequirements Section A/B.
On this occasion the completion and handling of the paperwork by the duty engineeron the afternoon of 28 June 1995 was considered to be below the standard normallyexpected from a licenced engineer in the following areas:
a) The routine worksheet was not recorded in the aircraft worksheet referencebook and the entry to record the requirement for the duplicate inspection wasnot completed.
b) The non-routine aircraft worksheet was also not recorded in the aircraftworksheet reference book.
13
c) The replacement of the tail rotor bellows required the disassembly of part ofthe flying controls which was not required to be disassembled during the 100hour routine inspection. However, no entry was made on the worksheet torecord the disassembly or to require a duplicate inspection followingreassembly.
d) The maintenance manual reference for the disassembly/reassembly of the tailrotor pitch change mechanism was not included on the worksheet and therequired steps were not followed.
e) On completion of maintenance the non routine aircraft worksheet was filedin stores and not retained with the routine inspection worksheets. It wastherefore not readily available with the technical log for the duty engineer onthe morning of 29 June 1995 to peruse.
The practice by the engineer to only raise the non routine worksheet when the workon the aircraft was completed must also be questioned. The primary task was toreplace the tail rotor bellows but he also decided to replace the attachment bolt.When he raised the non routine aircraft worksheet at the end of the check therequirement to replace the attachment bolt was not recorded. It is considered, hadthis been entered onto the worksheet at the time the defect was noted, it would havebeen clearly identified as an open entry and may have prevented the event whichcaused the accident.
The inclusion of the requirement for a duplicate inspection as the last entry CHI theroutine worksheet can lead to misinterpretation, particularly if the specific item theentry refers to is not identified. It would be more appropriate for the duplicateinspection item of a routine worksheet to immediately follow the reassembly of thecontrol system to which it refers. This would avoid any possible ambiguity.
The engineer who certified the second inspection did not query or question the factthe task he was to carry out was not defined on the routine worksheet. By notclearly establishing which controls had been disturbed the objective of the duplicateinspection was not satisfied.
2.4 The installation of the secondary retention device
The secondary retention device is a black polyamid collar which locates over thebolt securing the pitch change rod to the pitch change mechanism. Although it iseasy to verify its correct installation, the colour of the device does not contrast withthe surrounding structure. A device which provides a greater colour contrast mayassist engineering and flight crews to identify more readily when the device is notinstalled on the aircraft.
14
3. CONCLUSIONS
3.1 Findings
a) The aircraft had been maintained in accordance with its approved aircraftmaintenance schedule and there were no pre-existing defects that contributed to theaccident.
b) The pilot was fit at the time of the accident and there were no relevant medicalfactors.
c) The weather and air traffic control were not factors in the accident.
d) The emergency landing following loss of directional control was executed skilfullyby the pilot.
e) The tail rotor pitch change spider was disconnected from the tail rotor gearbox pitchchange rod as a non-routine maintenance task on the afternoon of the 28 June 1995.
f) The engineer performing the replacement of the tail rotor bellows did not adhere tothe required procedures contained in the maintenance manual and the associatedService Letter.
g) The engineer did not record the requirements for additional work at the time whendefects were identified.
h) The disassembly of the tail rotor pitch change mechanism was not recorded on anaircraft non-routine worksheet.
i) A duplicate inspection of the disturbed flying control as required by the ApprovedMaintenance Schedule was not called up.
j) The duplicate inspection requirement listed on the 100 hour routine worksheet wasnot specified.
k) The aircraft was returned to service without a cotter pin and a secondary retentiondevice fitted around the single nut and bolt which secures the tail rotor pitch changemechanism to the tail rotor pitch change rod.
1) The additional non-routine worksheet was not cross-referenced to the routineworksheet and was not readily available to the morning shift duty engineer who wasto complete the duplicate inspection on the aircraft.
m) The maintenance organisation had no procedures for shift handovers.
15
3.2 Causes
The following causal factors were identified:
a) The accident resulted from loss of directional control due to the tail rotor pitchchange mechanism becoming detached from the tail rotor pitch change rod.
b) The tail rotor pitch change mechanism became detached from the tail rotor pitchchange rod because the requirements of the maintenance manual were not adheredto:-
i) The cotter pin which locks the nut to the bolt that secures the pitch change spiderto the pitch change rod was not installed.
ii) The secondary retention device, comprising a guard collar, which prevents theloss of the bolt securing the pitch change spider to the pitch change rod was notinstalled.
c) The Approved Maintenance Schedule requirement to carry out a duplicateinspection on the disturbed flying control was not documented or carried out.
16
4. SAFETY RECOMMENDATIONS
4.1 Heliservices should review their procedures and, where necessary, define standardsfor maintenance and documentation completion in addition to requirements.
4.2 Heliservices should introduce a procedure for shift handovers which will clearlyidentify incomplete maintenance items to the succeeding shift engineer.
4.3 Heliservices should review their quality system to introduce procedures which willidentify when maintenance practices, including the completion of documentation,fail to meet with company standards or regulatory requirements.
4.4 Eurocopter (Aerospatiale) should consider producing the poly amid collar partnumber 3160S.33.30.067 in a colour which contrasts with the pitch changemechanism.
17
AoDendix 1
Needle bearing Angular contact bearings
Pitch change link
Pitch change spider
Blade sleeve
Lubricator
Lubricator
Tail Rotor Head Pitch Change Mechanism
Appendix 1
Tail Rotor Head Pitch Change Mechanisir
Appendix 2
BEFORE MODIFICATION
( AFTER MODIFICATION
Locking wire
Secondary Retention Device on Pitch Change Mechanism
* \
*f
\
\\
0* \
Wreckage Plot
Appendix 4
Aircraft Wreckage
General View
Aircraft Wreckage
Appendix 4
Main Rotor Assembly
Appendix 4
Aircraft Wreckage
Main Rotor Assembly
Appendix 4
Aircraft Wreckage
Tail Boom
Appendix 4
Aircraft Wreckage
Tail Rotor Assembly
Appendix 4
Aircraft Wreckage
Skid
HKP 363.124 H7 B96Hong Kong. Civil AviationDept. Accidents InvestigationDivision.
Date Due
Printed by the Government Printer, Hong Kong 7000886—4L—3/96Printed on paper made from woodpulp derived from renewable forests
