AIRCRAFT ACCIDENT REPORT 1/96 ACCIDENTS INVESTIGATION DIVISION CIVIL AVIATION DEPARTMENT HONG KONG

Transcription

1 AIRCRAFT ACCIDENT REPORT 1/96 ACCIDENTS INVESTIGATION DIVISION CIVIL AVIATION DEPARTMENT HONG KONG Report on the accident to Aerospatiale SA315B Lama VR-HJG 8 km west of Hong Kong Sek Kong Airfield on 29 June 1995 HKP H7 B96 HONG KONG GOVERNMENT

2 THE UNIVERSITY OF HONG KONG LIBRARIES Hong Kong Collection

3 R UK. J& *ft*tt*66 CIVIL AVIATION DEPARTMENT 46th floor, Queensway Government Offices, 66, Queensway, Hong Kong. OUR REF: YOURREF: TEL NO. CABLES: AIRCIVIL HONGKONG TELEX: CAD HK His Excellency the Governor, Hong Kong Government House Hong Kong Sir, I have the honour to submit the report by Mr. K.F. Cheung, an Inspector of Accidents, on the circumstances of the accident to Aerospatiale SA315B, VR-HJG, which occurred in Hong Kong on 29 June I have the honour to be Sir, Your Excellency's obedient servant R. A. Siegel Director of Civil Aviation

4 BIB.REG.NO. DATERHTD 24 JAN CLASS NO. AUTHOR NO. REBOUND

5 Contents SYNOPSIS Page i 1. FACTUAL INFORMATION 1.1 History of the flight Injuries to persons Damage to aircraft Other damage Personnel information Aircraft information Meteorological information Aids to navigation Communications Aerodrome information Flight recorders Wreckage and impact information Medical and pathological information Fire Survival aspects Tests and research Organizational and management information Additional information Useful or effective investigation techniques ANALYSIS 2.1 General The recognition of working procedures Certification of work accomplishment The installation of the secondary retention device CONCLUSIONS 3.1 Findings Causes SAFETY RECOMMENDATIONS 17

6 5. APPENDICES Tail rotor head pitch change mechanism Appendix 1 Secondary retention device on pitch change mechanism Appendix 2 Wreckage plot Appendix 3 Photographs of aircraft wreckage Appendix 4

7 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 Kong Latitude: 22 25'43.7" N Longitude: '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) SYNOPSIS The accident was notified to the Accidents Investigation Division of the Civil Aviation Department (CAD) by the operator on the morning of the 29 June The investigation by a team 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 the erection of electricity pylons in the New Territories. The operation was in accordance with visual flight rules (VFR) in uncontrolled airspace. At 0910 hours (0110 hours UTC) the pilot made 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 applied collective pitch to stabilise in the hover. The aircraft started to develop a yaw to the left which did not respond to the right hand pedal input applied by the pilot. While positioning the aircraft away 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 over onto its side and sustained major damage. There were no injuries to the pilot or persons on the ground. The investigation identified that the loss of yaw control was due to the tail rotor gearbox pitch change rod becoming detached from the mechanism which adjusts the pitch of the tail rotor blades in response to control pedal inputs. The pitch change rod became detached from the pitch change mechanism following the loss of the single attachment bolt in flight. This in turn was due to a cotter pin and a secondary retention device not being reinstalled in accordance with the requirements of the maintenance manual during maintenance carried out on the aircraft prior to the accident flight.

8 I. FACTUAL INFORMATION 1.1 History of the flight During the afternoon prior to the day of the accident the aircraft was positioned to the operator's hangar at Sek Kong airfield to enable a routine 100 hour inspection to be carried out. The afternoon duty engineer carried out maintenance on this aircraft and then went off shift at approximately 2000 hours (1200 hours UTC). The following morning the duty engineer arrived at approximately 0720 hours (2320 hours UTC on the 28 June 1995) and carried out a duplicate inspection on the aircraft which was the only recorded uncompleted item of maintenance from the previous afternoon. After this the aircraft was released for service for the day's flying program. The aircraft was due to carry out a number of flights which involved underslung load operations transporting concrete for the erection of power line towers. The pilot arrived at the operator's base at around 0730 hours (2330 hours UTC on the 28 June 1995). He commenced his first flight at approximately 0830 hours (0030 hours UTC) and had delivered several buckets of concrete at a site near Tai Lam Gap. He then flew back to the base at Sek Kong to replace the underslung load chain with a shorter 30 foot chain. An empty concrete bucket was hooked up and the aircraft flew to a concrete pick up point coded BS38(H) in Tan Kwai Tsuen Quarry, which was the site of the accident. The aircraft arrived at BS38(H) and flared into a hover. As the pilot lowered the bucket to the ground and applied collective pitch the aircraft started to yaw to the left. Directional control was applied to stop the yaw but there was no response even with full tail rotor pedal input. The pilot reported that he raised the collective pitch slightly to move the aircraft away from workmen on the ground below. At this point the aircraft started to spin to the left and became uncontrollable, the pilot immediately closed the fuel shutoff cock, shutting down the engine, and proceeded to carry out an emergency landing. The aircraft continued to spin and made approximately three turns before it impacted the ground where it rolled over and came to rest on its right side. The pilot, who was uninjured, vacated the aircraft and reported the accident to his company. The aircraft was examined at the accident site by inspectors from the Accidents Investigation Division of the Civil Aviation Department. A preliminary inspection of the tail rotor pitch change mechanism revealed that the attachment bolt which secures the tail rotor pitch change spider to the tail rotor pitch change rod was missing.

9 1.2 Injuries to persons Injuries Crew Passengers Others Fatal Serious Minor/None 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 was severely 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 to the tail rotor gearbox, hub and blades. The upper cabin assembly was severely damaged and both the left and right longitudinal beams of the lower cabin assembly were distorted. The right hand skid and the forward right hand skid leg were damaged. 1.4 Other damage No other damage was reported. 1.5 Personnel information 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 until 24 July 2000 Aerospatiale SA315B Eurocopter (France) AS355N 29 July 1994, Class 1, no limitations, valid until 30 July February May 1995

10 Flying experience: Total flying hours: 4,777.4 hours Total hours on type: 2,077.0 hours Hours in preceding 7 days: 24 hours Hours in preceding 28 days: 60 hours Rest period before duty on day of accident flight: 10 hours Maintenance engineer (Afternoon shift on 28 June 1995 local time) Licence: Type ratings held: Male aged 39 years Hong Kong Aircraft Maintenance Engineer's Licence valid until 15 June 1996 Category A&C (Aircraft/Engines) Aerospatiale SA315B with Artouste IIIB. Experience: Total experience: Type ratings held : 6 years 7 months Maintenance engineer (Morning shift on 29 June 1995 local time) Male aged 45 years Licence: Type ratings held: Hong Kong Aircraft Maintenance Engineer's licence valid until 16 February Category A&C (Aircraft/Engines) Turbine Engined Gyroplanes/ Helicopters Paragraph 7.3 (which includes SA315B) Experience: Total experience: Type ratings held: 28 years 17 years Maintenance assistant Licence: Male aged 34 years None Experience: 5 years engaged in aircraft servicing.

11 1.6 Aircraft information 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 weight with external load: Actual aircraft weight at time of accident: Maximum permissible under slung load: Estimated weight of under slung load at the time of accident: Estimated fuel remaining at the time of the accident: Aircraft centre of gravity at time of accident: Aerospatiale SA315BLama 2601 June 1981 Registered in the name of Heliservices (Hong Kong) Limited Transport Category (Passenger), last renewed from 4 November 1994 and valid until 3 November 1995 Valid until 6,609.4 Total Aircraft hours or 10 June 1996 whichever is sooner 6,305.1 hours Turbomeca Artouste IIIB 2,300 kg (5,070 Ib) Unknown but did not exceed the maximum authorised weight 1,136 kg (2,500 Ib) 100 kg (220 Ib) Unknown but the tank was not empty In normal range

12 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. The rate of turn will be dependent on the amount of power that was applied, and the weight of the aircraft, at the time of the failure." "OVER TERRAIN UNFAVOURABLE TO IMMEDIATE AUTOROTATIVE LANDING Reduce collective-pitch just sufficiently to achieve the best compromise between the rate 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 is imperative to shut down the engine by closing the fuel shut-off cock, and accomplish the flare-out, maintaining a constant height above the ground until forward 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 by hitting an obstacle) full low collective-pitch must be applied, even if this is to cause a very hard landing, and shut down the engine by closing the fuel shut-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 main rotor blade pitch is controlled by the cyclic and collective controls. The pitch of the tail rotor is controlled by foot pedals. The tail rotor provides anti-torque correction and heading control by varying the pitch of the tail rotor blades to counteract torque generated by the main rotor. The tail rotor head is of the three hinged blade type which are connected by pitch change links to a pitch change spider. The pitch change spider is in turn attached to a pitch change rod which is part of the tail rotor gearbox. Attachment is by a single bolt with the nut secured by a cotter pin. The movement of the pitch change rod varies with inputs from the pilot's pedals which are connected to the cable drum on the tail rotor gearbox. The tail rotor head pitch change mechanism is shown at Appendix No. 1. The single bolt attachment of the pitch change spider to the pitch change rod is a vital 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 recommended Service Bulletin No on the 1 February 1977 to provide a secondary retention device to prevent the loss of the bolt in the event of the nut becoming detached. The secondary retention device is a polyamid collar which is positioned on the shaft of

13 the pitch change rod and fits over the attachment bolt. See Appendix No. 2. Service Bulletin.No 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 a witness stationed at the accident site, were considered to be good. He said it was similar to the weather conditions two hours later when he was interviewed at the same 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 Information Service provided by the Royal Air Force Air Traffic Control on MHz at Sek Kong Airfield. The aircraft was airborne from the operator's base (in Sek Kong) at 0838 hours (0038 hours UTC) and proceeded to Tai Lam Sector. At 0900 hours (0100 hours UTC) the aircraft checked operations normal with Sector Information Service which was acknowledged.. That was the last radiotelephony (RT) communication recorded on the tape. At 0930 hours (0130 hours UTC), a phone call was received at Sek Kong Tower from the aircraft operator advising of the aircraft accident Aerodrome information Not applicable Flight recorders There was no requirement for a flight recorder to be installed and none was fitted on this aircraft Wreckage and impact information As recalled by the ground witness the aircraft spun about three turns before it impacted the ground. The pilot stated that the aircraft hit the ground on its right

14 hand skid and then rolled over onto its right side. There were no apparent impact marks but.this fact was supported as the aircraft right hand skid was found to be severely distorted with the forward leg fractured and no damage was found on the left hand skid. The wreckage when inspected was resting on soft grass and was complete, not having broken up on impact. The most obvious damage was to the main rotor with all three blades destroyed and the right hand skid damaged as described above. Refer to Appendix No.3 and Appendix No Medical and pathological information The pilot was medically examined shortly after the accident. It was concluded by the medical officer that the pilot was fit at the time of the accident and there were no relevant medical factors relating to the reported events. Blood and urine samples were sent to the government forensic laboratory for alcohol and drug screening, there were no significant findings. There were no other injuries Fire There was no fire 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 damaged and distorted. The cabin door operated correctly and provided the pilot a viable escape path Test and Research There were no specific tests or research carried out Organizational and management information Heliservices (Hong Kong) Limited holds an Air Operators Certificate which enables it to undertake flights for the purpose of public transport in accordance with the conditions specified in the certificate. Its maintenance organisation is approved in accordance with the Air Navigation (Overseas Territories) Order 1977 and complies with Hong Kong Aviation Requirements 145. The maintenance facility is managed by a Chief Engineer assisted by three licenced engineers.

15 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 out following the accident. Following completion of the day's flying on the 28 June 1995 the aircraft was positioned to the operator's base at Sek Kong airfield where a 100 hour inspection was to be carried out. This was a routine inspection required by the Approved Maintenance Schedule CAD/MS/SA315B/HS4 Rev. O. To facilitate and assist the engineers carrying out inspections, the company print a routine worksheet from a database which lists the items to be accomplished. The duty engineer who was to carry out the inspection was on the afternoon shift from 1300 hours (0500 hours UTC) to 2000 hours (1200 hours UTC). The company had recently introduced a two shift system to meet operational needs. The inspection on the aircraft commenced at approximately 1545 hours (0745 hours UTC) and the engineer was assisted by a non-licenced maintenance assistant. One item of the routine inspection required the three pitch change links, which connect the pitch change spider to the tail rotor blades, be disconnected to complete a check on the tail rotor blade hub bearings. When carrying out this check the engineer noted that a leather bellows, which is fitted over the tail rotor pitch change rod to prevent contamination of the tail rotor head, was in poor condition and decided to replace it. The replacement of the bellows required the disconnection of the pitch change spider from the pitch change rod. The engineer had carried out this task on many occasions and as it was a simple task he did not make reference to the aircraft maintenance manual. The required procedure for the disconnection of the pitch change spider is described in the maintenance manual Chapter The replacement of the bellows was not an item required by the Approved Maintenance Schedule and was therefore not referenced on the routine worksheet. The company provides aircraft worksheets, reference HS/ENG/016, which are used to record defects, the work required and carried out additional to the routine inspection. The aircraft worksheet also requires the certifying engineer to complete a Certificate of Compliance for the work carried out. The engineer did. not raise an aircraft worksheet at the time he decided to replace the bellows. When the bolt which secures the pitch change spider to the pitch change rod was removed the engineer saw that the shank was worn and he made a mental note to change the bolt during re-assembly. The items removed, which comprised the bolt, castellated nut, cotter pin, secondary retention device and the worn bellows together with its associated clamp were placed on a workstand adjacent to the aircraft. At this point in time the engineer stopped work on the tail rotor assembly to carry out an inspection on the engine at the request of another engineer who was on duty on the morning of the 29 June 1995, the day of the accident. This engineer had come to work specifically to carry out an inspection on the engine to support a future application for a life extension programme. After the inspection was completed the second engineer returned home. There was no record of this inspection recorded in

16 the aircraft documentation. After assisting with the engine inspection, the engineer drained the tail rotor gearbox oil. Again this maintenance was not recorded in the aircraft documentation. He then fitted the new bellows onto the tail rotor pitch change rod and using the old bolt re-aligned the pitch change spider onto the pitch change rod. He installed the nut and tightened it up. At this point he remembered that he intended to change the bolt and did not proceed to insert the cotter pin to lock the castellated nut. He carried on and re-assembled the pitch change links between the pitch change spider to the tail rotor blade sleeves. He recalled that he completed other maintenance activities in the vicinity of the tail rotor and then took a break. During this break, although the engineer noted that the maintenance assistant had cleaned the area around the aircraft of the items used on the check, he was not aware that the old bellows together with the secondary retention device, which he left on the workstand, had been removed as well. On his return to the aircraft the engineer forgot about his intention to replace the bolt in the pitch change mechanism and went on to complete other maintenance tasks on the aircraft. The engineer then completed the aircraft check paperwork and signed all the entries to signify the work had been completed. The last item on the routine checksheet is a duplicate inspection which the engineer signed for the first inspection. The duplicate inspection statement, which is pre-printed on the routine worksheet, leaves a space where the engineer who has performed the disassembly of a control system must identify the items on the routine worksheet which are the subject of the duplicate inspection. The duplicate inspection requirements were not identified by the engineer. The engineer subsequently raised an aircraft worksheet which recorded that the tail rotor bellows had been replaced and signed the Certificate of Compliance. There was no mention on this worksheet that the pitch change spider had been disconnected from the pitch change rod and no duplicate inspection was called up. The engineer recalled that he placed the aircraft worksheet in the stores to alert the storeman that a bellows had been used and to re-order for stock. The routine worksheet was placed with the aircraft technical log for the attention of the duty engineer the next morning. The engineer considered the check and the paperwork were complete at approximately 1845 hours (1045 hours UTC) following which he went off shift. On the morning of the 29 June 1995 the duty engineer arrived at approximately 0720 hours (2320 hours UTC on the 28 June 1995). Prior to the aircraft departing for the day's flying he reviewed the technical log and the check paperwork. He then proceeded to carry out a duplicate inspection on the aircraft following which he signed for the second inspection and the aircraft was then released for service. The duplicate inspection he carried out comprised the tail rotor pitch change links for correct 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 specific check of the pitch change spider to pitch change rod for correct assembly and also did not recall seeing the aircraft worksheet which recorded the replacement of the tail rotor bellows. 10

17 Findings at aircraft crash site On being notified of the accident, the duty engineer attended the crash site where he noted the bolt which secures the tail rotor pitch change spider to the tail rotor pitch change rod and the secondary retention device were missing. The secondary retention device was later found at the operator's maintenance base Aircraft maintenance documentation The company use a pre printed worksheet for the routine work requirements required by the Approved Aircraft Maintenance Schedule and an aircraft worksheet to record any additional or non routine work carried out. An aircraft worksheet reference book is provided to record a sequential reference number for routine and non routine worksheets used during aircraft maintenance. No references were entered for this particular maintenance inspection on VR-HJG. There is no provision on the routine worksheet to indicate or record if any non-routine worksheets have been raised and there was no tally sheet to record the documentation raised during a scheduled maintenance inspection. A review of the routine worksheet for the 100 hour inspection revealed a number of anomalies. The tasks are grouped together by subjects and systems. The lubrication tasks were all pre fixed however this did not align with the maintenance 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 refers." Therefore this item contained three separate tasks under the heading of lubrication. The tail rotor spin check for hard points was the task that required the disconnection of the tail rotor pitch links and this was the only break down of the flying controls which required a duplicate inspection during the 100 hour inspection. This task was derived from a manufacturer's service letter No , however, this was not referred to on the routine worksheet. When interviewing the engineers, it became apparent that the duplicate inspection called up in the routine worksheet is considered to apply to more items than just the pitch change links. The engineer who carries out the duplicate inspection also checks the flying control movement and certain oil and fuel filters for security and locking. These additional items are company requirements and are over and above the duplicate inspection required by the regulations and were not recorded individually on the aircraft routine worksheets. Aircraft worksheets for recording non routine maintenance tasks require the engineer 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 is incumbent upon the engineer to record the requirement for a duplicate inspection to be carried out following reassembly. To facilitate this, the company provide a stamp which prints the duplicate inspection requirement. 11

18 Company procedures A two shift system, mornings and afternoons, had been recently introduced by the company and there was a one hour overlap at the time of the afternoon shift change but no overlap between the afternoon and morning shift. There was no formal shift handover procedure in the Company Procedures manual. The Company Procedures manual describes in general the aircraft documentation used by the company but did not specify the standard required for completion. Item 5 of the general instructions in the Heliservices Approved Maintenance Schedule requires duplicate inspections to be carried out on engine controls and flight controls in accordance with British Civil Airworthiness Requirements whenever they are disturbed. However, there were no further instructions on how they should be carried out and documented Engineering standards The maintenance organisation is of a small size with 4 certifying engineers holding type rated licences. As type rated licenced engineers they are expected to work to high individual standards and the Company Procedures manual specified requirements which had to be satisfied but did not define standards to be achieved, particularly in respect of the completion of aircraft documentation Corrective actions taken by the Maintenance Organisation Immediate corrective actions were taken by the organisation. The more significant actions were: The introduction of Engineering Notices, pending amendment of the Company Procedures manuals, to define standards for duplicate inspections and documentation, worksheet completion and the recording of documents used during a maintenance inspection. The introduction of a shift handover procedure to ensure engineers are apprised of work carried out and any outstanding items. A procedure was introduced to fix a readily visible flag to the area of the aircraft which requires the duplicate inspection Useful or effective investigation techniques No special investigation techniques were used during the investigation of this accident. 12

19 2. ANALYSIS 2.1 General Examination of the wreckage confirmed that the bolt which secures the tail rotor pitch 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 control inputs had no effect on the tail rotor blade pitch angle. The aircraft was released for service following maintenance without a cotter pin to lock the castellated nut to the bolt securing the pitch change mechanism to the pitch change 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 nut vibrated off the bolt leading to the loss of the bolt and resulting in the loss of directional control. 2.2 The recognition of working procedures The task to disconnect the tail rotor pitch change mechanism to change the bellows is not a complex task. However, the resulting accident serves as a reminder that no matter how simple a task may be, if it is not carried out strictly in accordance with the maintenance instructions it can have potentially catastrophic consequences. The fact that critical tasks are not complex and are routinely carried out requires vigilance 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 maintenance work carried out should be recorded. Prior to the granting of an Aircraft Maintenance Engineer's Licence an applicant is examined on the requirements for the certification of work accomplished on aircraft. This includes the requirements for duplicate inspections which are specified in detail in British Civil Airworthiness Requirements Section A/B. On this occasion the completion and handling of the paperwork by the duty engineer on the afternoon of 28 June 1995 was considered to be below the standard normally expected from a licenced engineer in the following areas: a) The routine worksheet was not recorded in the aircraft worksheet reference book and the entry to record the requirement for the duplicate inspection was not completed. b) The non-routine aircraft worksheet was also not recorded in the aircraft worksheet reference book. 13

20 c) The replacement of the tail rotor bellows required the disassembly of part of the flying controls which was not required to be disassembled during the 100 hour routine inspection. However, no entry was made on the worksheet to record the disassembly or to require a duplicate inspection following reassembly. d) The maintenance manual reference for the disassembly/reassembly of the tail rotor pitch change mechanism was not included on the worksheet and the required steps were not followed. e) On completion of maintenance the non routine aircraft worksheet was filed in stores and not retained with the routine inspection worksheets. It was therefore not readily available with the technical log for the duty engineer on the morning of 29 June 1995 to peruse. The practice by the engineer to only raise the non routine worksheet when the work on the aircraft was completed must also be questioned. The primary task was to replace 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 the requirement to replace the attachment bolt was not recorded. It is considered, had this been entered onto the worksheet at the time the defect was noted, it would have been clearly identified as an open entry and may have prevented the event which caused the accident. The inclusion of the requirement for a duplicate inspection as the last entry CHI the routine worksheet can lead to misinterpretation, particularly if the specific item the entry refers to is not identified. It would be more appropriate for the duplicate inspection item of a routine worksheet to immediately follow the reassembly of the control system to which it refers. This would avoid any possible ambiguity. The engineer who certified the second inspection did not query or question the fact the task he was to carry out was not defined on the routine worksheet. By not clearly establishing which controls had been disturbed the objective of the duplicate inspection was not satisfied. 2.4 The installation of the secondary retention device The secondary retention device is a black polyamid collar which locates over the bolt securing the pitch change rod to the pitch change mechanism. Although it is easy to verify its correct installation, the colour of the device does not contrast with the surrounding structure. A device which provides a greater colour contrast may assist engineering and flight crews to identify more readily when the device is not installed on the aircraft. 14

21 3. CONCLUSIONS 3.1 Findings a) The aircraft had been maintained in accordance with its approved aircraft maintenance schedule and there were no pre-existing defects that contributed to the accident. b) The pilot was fit at the time of the accident and there were no relevant medical factors. c) The weather and air traffic control were not factors in the accident. d) The emergency landing following loss of directional control was executed skilfully by the pilot. e) The tail rotor pitch change spider was disconnected from the tail rotor gearbox pitch change rod as a non-routine maintenance task on the afternoon of the 28 June f) The engineer performing the replacement of the tail rotor bellows did not adhere to the required procedures contained in the maintenance manual and the associated Service Letter. g) The engineer did not record the requirements for additional work at the time when defects were identified. h) The disassembly of the tail rotor pitch change mechanism was not recorded on an aircraft non-routine worksheet. i) A duplicate inspection of the disturbed flying control as required by the Approved Maintenance Schedule was not called up. j) The duplicate inspection requirement listed on the 100 hour routine worksheet was not specified. k) The aircraft was returned to service without a cotter pin and a secondary retention device fitted around the single nut and bolt which secures the tail rotor pitch change mechanism to the tail rotor pitch change rod. 1) The additional non-routine worksheet was not cross-referenced to the routine worksheet and was not readily available to the morning shift duty engineer who was to complete the duplicate inspection on the aircraft. m) The maintenance organisation had no procedures for shift handovers. 15

22 3.2 Causes The following causal factors were identified: a) The accident resulted from loss of directional control due to the tail rotor pitch change mechanism becoming detached from the tail rotor pitch change rod. b) The tail rotor pitch change mechanism became detached from the tail rotor pitch change rod because the requirements of the maintenance manual were not adhered to:- i) The cotter pin which locks the nut to the bolt that secures the pitch change spider to the pitch change rod was not installed. ii) The secondary retention device, comprising a guard collar, which prevents the loss of the bolt securing the pitch change spider to the pitch change rod was not installed. c) The Approved Maintenance Schedule requirement to carry out a duplicate inspection on the disturbed flying control was not documented or carried out. 16

23 4. SAFETY RECOMMENDATIONS 4.1 Heliservices should review their procedures and, where necessary, define standards for maintenance and documentation completion in addition to requirements. 4.2 Heliservices should introduce a procedure for shift handovers which will clearly identify incomplete maintenance items to the succeeding shift engineer. 4.3 Heliservices should review their quality system to introduce procedures which will identify 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 part number 3160S in a colour which contrasts with the pitch change mechanism. 17

24 AoDendix 1 Needle bearing Angular contact bearings Pitch change link Blade sleeve Lubricator Pitch change spider Lubricator Tail Rotor Head Pitch Change Mechanism

25 Tail Rotor Head Pitch Change Mechanisir Appendix 1

26 Appendix 2 BEFORE MODIFICATION ( AFTER MODIFICATION Locking wire Secondary Retention Device on Pitch Change Mechanism

27 * \ \ \ \ 0* \ *f

28 Wreckage Plot

29 Appendix 4 Aircraft Wreckage General View

30 Appendix 4 Aircraft Wreckage Main Rotor Assembly

31 Appendix 4 Aircraft Wreckage Main Rotor Assembly

32 Appendix 4 Aircraft Wreckage Tail Boom

33 Appendix 4 Aircraft Wreckage Tail Rotor Assembly

34 Appendix 4 Aircraft Wreckage Skid

35 HKP H7 B96 Hong Kong. Civil Aviation Dept. Accidents Investigation Division. Date Due

36 Printed by the Government Printer, Hong Kong L 3/96 Printed on paper made from woodpulp derived from renewable forests