CHC Scotia Sikorsky S-92A Loss of Tail Rotor Control Events
Sikorsky S-92A Loss of Tail Rotor Control Events (CHC Scotia G-WNSR, Total West Franklin Installation, Central North Sea) The UK Air Accidents Investigation Branch (AAIB) have issued a Special Bulletin on an occurrence involving Sikorsky S-92A G-WNSR of CHC Scotia on 28 December 2016, which they have classified as an Accident. This involved the failure of both the tail rotor pitch change shaft bearing and the servo piston rod itself, resulting in a total loss of tail rotor control, fortuitously without injury. We look at the background to this accident. The Accident Flight The S-92A was on a four-sector routing from Aberdeen to Total’s Elgin-Franklin field in the Central North Sea and back as Flight 21N, which departed Aberdeen at 07:15. The second sector was from the Elgin Process Utilities Quarters (PUQ) to the West Franklin wellhead platform, 3.3 nm to the south, with 2 crew and 9 passengers on-board. The West Franklin, whose topsides were constructed by Rosetti Marino, has a Bayards 21m, 12.8t aluminium helideck. The meteorological observation from the Elgin PUQ at 06:08 was of a surface wind from 220° at 17 kt. The AAIB say: As the helicopter [on a heading of 270°] lifted from the Elgin PUQ helideck it yawed unexpectedly to the right through 45°. The commander applied full left yaw pedal, checked the rotation and landed back onto the deck. The flight crew discussed the likely cause, which they thought to have been the result of local turbulence or wind effects created by the platform structures which, anecdotally, is not uncommon for this helideck. They decided to continue and during the subsequent lift off into the hover the commander applied left yaw pedal, the helicopter responded and turned to the left; all control responses appeared normal. The commander then climbed to 500 ft for the brief transit… The helicopter made a normal approach and deceleration to the West Franklin and crossed over the helideck. During the descent to land, at approximately 4 ft above the helideck, it yawed rapidly to the right, reaching a maximum rate of 30 degrees per second. At the same time it rolled 20° to the left, at which point the left main landing gear contacted the helideck. It continued to yaw to the right on its left mainwheels and nosewheels before the right mainwheels contacted the surface [of the helideck, causing damage to deck and the left outer main wheel rim]. The helicopter came to rest on a heading of 041° having rotated through 187°. The helicopter was shut down and the crew and passengers disembarked; there were no injuries. The helicopter was subsequently craned from the helideck onto a ship [the Ben Nevis] and recovered to Aberdeen [arriving on the morning of 30 December 2016]. Reporting The operator transmitted a Mandatory Occurrence Report (MOR) to the UK Civil Aviation Authority (UK CAA) on 28 December 2016. It is understood that an industry lead investigation commenced promptly and the occurrence, and the damage to the helideck, was mentioned in the local press on 30 December 2016. The AAIB say they did not however become aware of it until 5 January 2017 (the same day that photographs of the damaged helideck emerged in the local press). Investigation Once the panels were removed it was immediately apparent that the tail rotor servo piston was damaged. The servo was removed and revealed that...
read moreS-92A Flying Control Restriction on Wiring Loom
S-92A Flying Control Restriction on Wiring Loom A pilot recently reported a restriction of main rotor cyclic movement in the forward left quadrant of a Sikorsky S-92A according to a Service Difficult Report (SDR) submitted to the Civil Aviation Safety Authority (CASA) in Australia. The subsequent maintenance investigation found that a cyclic wiring loom was preventing full movement to the stop. The wiring loom was rerouted to eliminate the restriction. The SDR provides no further details on how, when or why the loom became misrouted. See also our previous articles: C-130 Fireball Due to Modification Error B767 Engine Fire – Ignition from Misrouted / Chaffed Cables UPDATE 13 March 2017: The AIB Nigeria have only just released their report into a hydraulic pipe chafing event that caused a fire on 27 February 2013 on S-92A 5N-BOA. It is rather unfair however of the AIBN to complain that the operator did not did not challenge the serial number applicability of an earlier 2008 Sikorsky ASB that (by implication) was to address production defects with a once off inspection. Aerossurance is pleased to sponsor the 2017 European Society of Air Safety Investigators (ESASI) 8th Regional Seminar in Ljubljana, Slovenia on 19 and 20 April 2017. Registration is just €100 per delegate. To register for the seminar please follow this link. ESASI is the European chapter of the International Society of Air Safety Investigators (ISASI). UPDATE 6 August 2018: In-Flight Flying Control Failure: Indonesian Sikorsky S-76C+ PK-FUP UPDATE 30 May 2019: PA-34 Electrical Short Melted Rudder Cable UPDATE 18 November 2020: Embraer ERJ-190 EWIS Production Quality a Factor in Fire UPDATE 27 December 2020: Fire-Fighting AS350 Hydraulics Accident: Dormant Miswiring UPDATE 8 February 2021: RCAF Investigate Defect on Newly Delivered CH-148 Cyclone (S-92) UPDATE 17 September 2022: Canadian B212 Crash: A Defective Production Process UPDATE 25 May 2025: CHC Sikorsky S-92A Seat Slide Surprise(s) Aerossurance has extensive air safety, operations, SAR, airworthiness, design assessment, certification, human factors, aviation regulation and safety analysis experience. For practical aviation advice you can trust, contact us at: enquiries@aerossurance.com Follow us on LinkedIn and on Twitter @Aerossurance for our latest...
read moreHROs and Safety Mindfulness
High Reliability Organisations (HROs) and Safety Mindfulness As part of research into ‘Resolving the Organisational Accident’, an EU aviation research project, called Future Sky, initiated by the association of European Research Establishments in Aeronautics (EREA), has been examining the topic of ‘Safety Mindfulness’. The concept is that if front-line staff are aware of the possible threats they can anticipate and mitigate most of them. However there is a traditionally a time delay after new threats emerge before all operational personnel received information on the threat. This Safety Mindfulness research “aims to provide much faster and effective processes to give operational people these types of information”. The authors of their first report on the concept are Nick McDonald, Tiziana Callari and Daniele Baranzini (all from Trinity College Dublin) and Rogier Woltjer and Björn Johansson (of FOI). NLR are programme managing the research and the project manager is Barry Kirwan of Eurocontrol. It also includes contributors from KLM. Another Future Sky project has recently investigated the concepts of organisational safety intelligence (the safety information available) and executive safety wisdom (in using that to make safety decisions). We discussed that study in our article: Safety Intelligence & Safety Wisdom 1) Origins of Mindfulness a) High Reliability Organisations (HROs) The Safety Mindfulness Concept develops the original Mindfulness concept from Weick and Sutcliff (2007) and aims to…: …develop and demonstrate a practical method of maintaining Safety Mindfulness in operational situations, by maintaining the (top-down) feed-forward of risk information from safety to operations, (bottom-up) feedback from operations to safety people, and (horizontal) safety information sharing in the operational layer, which includes supervisors. Weick and Sutcliff developed the High Reliability Organisation (HRO) concept were an: HRO can be referred to as a set of organising processes that allow an organisation to continuously operate under trying conditions, reduce the impacts of accidents, and help with the recovery process. HROs strive to avoid errors by stressing a commitment to consistently safe and reliable operations. Mindfulness is a collective capability comprises five HRO processes (Weick, et al. 1999; Weick and Sutcliffe, 2007) that the Future Sky team summarise as: (1) Preoccupation with failure (regularly and robustly discussing potential threats to reliability), (2) Reluctance to simplify interpretations (developing a nuanced understanding of the context by frequently questioning the adequacy of existing assumptions and considering reliable alternatives), (3) Sensitivity to operations (integrating the understanding into an up-to-date big picture), (4) Commitment to resilience (recognising the inevitability of setbacks and thoroughly analysing, coping with, and learning from them) and (5) Under-specification of structure (deferring to expertise rather than authority when making important decisions). The Future Sky authors note that: A fundamental idea in Weick’s writing is that organisations that encourage the sharing of narratives and storytelling will be more reliable than an organisation that does not, as “people know more about their system, know more of the potential errors that might occur and they are more confident that they can handle those errors that do occur because they know that other people have already handled similar errors” (Weick, 1987, p. 113). Weick goes as far as seeing storytelling and upholding narratives as a substitute for trial and error, pointing to the fact that in many organizations, error is not an option as it would have disastrous outcomes. Instead, near misses and successful performance or recovery is used to illustrate the kind of behaviours that is encouraged by the members of the organization....
read moreSafety Lessons from a Fatal Helicopter Bird Strike: PHI Sikorsky S-76C++
Safety Lessons from a Fatal Helicopter Bird Strike: PHI Sikorsky S-76C++ N748P Contracted to Shell Oil We look at a fatal accident that happened on 4 January 2009 that highlights a range of certification, modification, crew alerting, training and emergency response lessons. We also discuss current activity on helicopter bird strike certification requirements. The Accident Flight Sikorsky S-76C++ N748P of PHI took off from a heliport in Louisiana, destined for a Shell offshore installation in the Gulf of Mexico with two crew and 7 passengers aboard. The helicopter “established level cruise flight at 850 feet mean sea level and 135 knots indicated air speed” according to the US National Transportation Safety Board (NTSB) investigation report and: About 7 minutes after departure, the cockpit voice recorder recorded a loud bang, followed by sounds consistent with rushing wind and a power reduction on both engines and a decay of main rotor revolutions per minute. Due to the sudden power loss, the helicopter departed controlled flight… The helicopter crashed in marshland just 12 miles from the heliport. The Caledonian Airborne Emergency Locator Transmitter (ELT) activated. While there is normally a short delay until the COSPAS/SARSAT satellite system alerts the appropriate Rescue Coordination Centre (RCC), the USAF RCC only made contact with the operator 31 minutes after impact according to their accident report form. It was not until the wreckage had been visually identified (54 minutes after impact) by another of the operator’s helicopters that a US Coast Guard helicopter was dispatched. Miraculously one passenger was found alive, albeit very seriously injured. The NTSB N748P Accident Investigation The NTSB identified that the helicopter had suffered a bird strike: Examination of the wreckage revealed that both the left and right sections of the cast acrylic windshield were shattered. Feathers and other bird remains were collected from the canopy and windshield at the initial point of impact and from other locations on the exterior of the helicopter. Laboratory analysis identified the remains as coming from a female red-tailed hawk; The females of that species have an average weight of 2.4 pounds [1.1kg]. The acrylic windshield had been fitted in place of the production windshield after delivery (discussed further below). Located about 100mm behind the windscreen of the S-76C++ are two engine fire extinguisher T-handles. These… …are normally in the full-forward position during flight, and each is held in place by a spring-loaded pin that rests in a detent; aft pulling force is required to move the T-handles out of their detents. If the T handles are moved aft, a mechanical cam on each T-handle pushes the trigger on the associated [engine power control lever] ECL out of its wedge-shaped stop, allowing the ECL to move aft, reducing fuel to the engine that the ECL controls. The investigators determined: The impact of the bird on the canopy just above the windshield near the engine control quadrant likely jarred the fire extinguisher T-handles out of their detents and moved them aft, pushing both ECL triggers out of their stops and allowing them to move aft and into or near the flight-idle position, reducing fuel to both engines. A similar incident occurred on November 13, 1999, in West Palm Beach, Florida, when a bird struck the windshield of an S-76C+ [HEMS] helicopter, N276TH, operated by Palm Beach County. The bird did not penetrate the laminated glass windshield, but the impact...
read moreOur Top 10 Articles of 2016
Our Top 20 Articles of 2016 In 2016 Aerossurance’s digest of aviation and safety articles attracted twice as many readers as in 2015. As we prepare to start a new year we look back on the 10 most read articles in 2016 from the choice of over 400 on our website. In reverse order: Number 10: Retreating Blade Stall Incident During a patient transfer in Australia, an Emergency Medical Service Airbus Helicopters BK 117 dropped 4,000 ft after a loss of control in the cruise. No injuries were reported and the helicopter sustained minor damage the horizontal stabiliser end plates. These were struck by the main rotor blades, which themselves were undamaged. The Australian Transport Safety Bureau (ATSB) investigation report highlights the phenomena of retreating blade stall: The selected cruise speed of 115 kt was close to the calculated never exceed speed (VNE) for the conditions of 120 kt. In combination, the high all-up weight and speed required greater collective pitch, or main rotor blade angle. This placed the blades closer to their stalling angle of attack. The cruise altitude of 5,000 ft resulted in operation at a moderately high density altitude and in areas of moderate turbulence. These conditions, coupled with the effect of the already-discussed high all-up weight are known to be conducive to the onset of retreating blade stall at high speed. The uncommanded nose-up pitch and subsequent roll in the direction of the retreating blade indicated that retreating blade stall took place. Number 9: Fatigued Flight Test Crew Crosswind Accident The Icelandic Transportation Safety Board (ITSB), the RNSA, issued their report into a wheels up runway excursion accident that occurred on 21 July 2013 to Sukhoi RRJ-95B ‘Superjet 100’ 97005 during flight tests by Sukhoi at Keflavik airport. The RNSA concluded “that human factors played a significant role in this accident”. In particular significant fatigue was evident. Number 8: Fatal Wire Strike on Take Off from Communications Site The Transportation Safety Board of Canada (TSB) released their report on Airbus Helicopters AS350BA C-GBPS, operated by Canadian Helicopters (CHL), that departed a microwave communication site and fatally struck one of the microwave tower guy wires. The lack of effective risk assessment and landing site data jumps out in their report as does a casual approach to some pre-flight preparation. There are key survivability lessons too. Number 7: Critical Maintenance Tasks: EASA Part-M & -145 Change This article discussed Commission Regulation (EU) 2015/1536 . One of the most important parts of the change relates to Critical Maintenance Tasks (CMTs), which are defined as: …a maintenance task that involves the assembly or any disturbance of a system or any part on an aircraft, engine or propeller that, if an error occurred during its performance, could directly endanger the flight safety. The European Aviation Safety Agency (EASA) has said that this change: …addresses a safety issue related to the risk of errors made during the performance of critical maintenance tasks and the need for maintenance organisations to implement methods to capture those errors before the certificate of release to service is issued. The NPA was in part prompted by following three safety recommendations addressed to the Agency: AIBN recommendation 12/2006, Report on the aircraft accident at Bergen Airport Flesland, Norway, on 31 January 2005 involving ATR 42-320, OY-JRJ, operated by Danish Air Transport, when control problems were experienced an elevator bolts loosened and fell out. The self-locking nuts were not tightened with the required torque. UK AAIB Safety Recommendation 2005-123 in Report 3/2005 on the serious incident to Boeing 757-236, operated by British Airways, on 7 September 2003. Maintenance errors...
read moreCRJ-200 LOC-I Sweden 8 Jan 2016: SHK Investigation Results
CRJ-200 LOC-I Sweden 8 Jan 2016: SHK Investigation Results On 8 January 2016 Canadair CRJ-200 (CL-600-2B19) cargo aircraft SE-DUX of West Air Sweden was destroyed when it impacted remote terrain in Northern Sweden following a Loss of Control – Inflight (LOC-I). Both pilots were killed. The aircraft had departed Oslo-Gardermoen Airport, Norway 70 minutes earlier for Tromsø, Norway on a night mail and parcel service. The Swedish Accident Investigation Board (the Statens Haverikommission [SHK]) has recently published its accident report into an accident that is reminiscent of the LOC-I suffered by Airbus A330 F-GZCP operating flight AF447 in 2009. The Accident Flight The SHK say: The flight was uneventful until the start of the event, which occurred during the approach briefing in level flight at FL 330. The event started at 00:19:20 hrs during darkness without moonlight, clouds or turbulence. The lack of external visual references meant that the pilots were totally dependent on their instruments which, inter alia consisted of three independent attitude indicators. According to recorded data and simulations a very fast increase in pitch was displayed on the left attitude indicator. The pilot in command, who was the pilot flying and seated in the left seat exclaimed a strong expression. The displayed pitch change meant that the pilot in command was subjected to a surprise effect and a degradation of spatial orientation. The autopilot was, most probably, disconnected automatically, a “cavalry charge” aural warning and a single chime was heard, the latter most likely as a result of miscompare between the left and right pilots’ [primary] flying displays (PFD). Both elevators moved towards nose down and nose down stabilizer trim was gradually activated from the left control wheel trim switch. The aeroplane started to descend, the angle of attack and G-loads became negative. Both pilots exclaimed strong expressions and the co-pilot said “come up”. About 13 seconds after the start of the event the crew were presented with two contradictory attitude indicators with red chevrons pointing in opposite directions. At the same time none of the instruments displayed any comparator caution due to the PFDs declutter function in unusual attitude. Bank angle warnings were heard and the maximum operating speed and Mach number were exceeded 17 seconds after the start of the event, which activated the overspeed warning. The speed continued to increase, a distress call was transmitted and acknowledged by the air traffic control and the engine thrust was reduced to flight idle. The crew was active during the entire event. The dialogue between the pilots consisted mainly of different perceptions regarding turn directions. They also expressed the need to climb. At this stage, the pilots were probably subjected to spatial disorientation. The aircraft collided with the ground one minute and twenty seconds after the initial height loss. The Accident Site The accident site and the wreckage did not show any evidence of an inflight break-up. Debris was found up to a distance of about 150 meters from the crater. Most parts were found in the crater and to the northeast of it. The SHK Accident Investigation The SHK say: The flight recorders were recovered and readout. Calculations and simulations were performed to reconstruct the event and showed that the aeroplane’s flight control system operated normally. The erroneous attitude indication on PFD 1 was caused by a malfunction of the...
read moreSeason’s Greetings from Aerossurance
Aerossurance sends its Season’s Greetings to all its customers, partners, suppliers, colleagues and friends. We also wish you all a safe and prosperous 2017! For aviation advice you can trust, contact Aerossurance at: enquiries@aerossurance.com Follow us on LinkedIn and on Twitter @Aerossurance for our latest...
read moreTime Pressures and Take-Off Trim Trouble
UPDATE Time Pressures and Take-Off Trim Trouble The Australian Transport Safety Bureau (ATSB) report on a loading related incident involving Embraer EMB-120 Brasilia, VH-ANQ, of at Darwin Airport, NT, on 6 August 2016. The Incident Flight At about 0530 Local Time, the flight crew arrived at the aircraft ready to perform flight TL414 from Darwin to Groote Eylandt, NT. The ATSB say: They discovered that the refueller was running late and the aircraft servicing had not been completed. The aircraft load information also arrived about 10 minutes late. In an attempt to depart on time, the first officer completed the trim sheet more quickly than usual and did not conduct their usual double check to confirm that it was completed correctly. At about 0555, the crew started the take-off roll. As the aircraft rotated, the captain (the pilot flying) noted the aircraft felt out of trim, so adjusted the trim and completed a normal rotation. After the initial climb, the captain asked to review the trim sheet. The captain found that the first officer did not include 584 kg of baggage and freight in the take-off trim setting calculation. The captain and first officer recalculated the aircraft trim and found the correct trim setting for the take-off should have been 0.8° nose-up. The crew rechecked the trim sheet which showed the aircraft was within all weight and balance limitations. The flight proceeded to Groote Eylandt without further incident. Crew Comments The first officer said that: Due to the late arrival of the loading paperwork and the passengers sitting in the aircraft longer than was usual, they felt pressured to complete the trim sheet quickly and pass it to the customer service officer who was standing behind them. The captain commented: As the first officer was approaching the end of their training, the captain felt comfortable with the first officer’s ability to complete the trim sheet without error. The company operating procedure required both flight crew to sight the trim sheet. However, this did not normally occur in operations. The pre-flight delays had compounded to give the first officer 10 minutes to complete the pre-flight paperwork instead of the usual 20 minutes. As part of the training, the captain wanted to observe how the first officer managed the pre-flight delays and did not assist unless requested. The day prior to the incident, the captain reported raising concerns regarding the pressure being placed on first officers training to become captains to complete the trim sheet in under two minutes. They felt that the focus during training should be on completing the trim sheets correctly before the speed naturally increases. It is better to take extra time to complete the trim sheet correctly and double check. If the time had been taken to double check, the error may have been identified. The captain felt company communications to flight crew had a large focus on flights departing on time. This placed pressure on the flight crew to rush their pre-flight preparations. The captain found the manual trim sheets used for EMB-120 operations laborious and presented a high risk of error. Safety Action The operators says: The company standard operating procedure ‘Completion of the Trim Sheet’ has changed from both flight crew being required to sight the trim sheet to include a requirement for both flight...
read moreThe Tender Trap: SAR and Medevac Contract Design
The Tender Trap: SAR and Medevac Contract Design AirMed and Rescue published an article in their Dec 2016 / Jan 2017 issue by Aerossurance‘s Andy Evans on how to tender and contract for Search and Rescue (SAR) and medevac services (click this link for the full 3 page article online). While there are some unique aspects to SAR and medevac contracts, many of the principles discussed are common for all types of contracted air service. Aerossurance has extensive experience in the areas of aviation service contracting: Requirements analysis Market analysis Tender preparation Bid evaluation Bidder organisational capability assessment / audit Contract technical definition On contract assurance We have helped organisations in the defence, oil, gas, mining, logistics, environmental services and wind energy sectors contract for over 80 aircraft (helicopters and fixed wing). These have been for a range of transport, training and special mission contracts around the world, lasting from just a few weeks to 25 years. These contracts are worth over a £1 billion in total. See our earlier article: Increasing SAR Use by the Oil & Gas Industry UPDATE 31 January 2017: Aerossurance’s Andy Evans has also written an article in the current issue of the International Federation of Airworthiness (IFA) Airworthiness Matters magazine on: Next Generation Maintenance Human Factors. UPDATE 4 October 2017: Irish Coast Guard (IRCG) Select Aerossurance as SAR Aviation Consultancy UPDATE 16 May 2019: Survey Aircraft Fatal Accident: Fatigue, Fuel Mismanagement and Prior Concerns UPDATE 13 July 2019: Helicopter Wirestrike During Powerline Inspection UPDATE 5 March 2020: HEMS AW109S Collided With Radio Mast During Night Flight UPDATE 19 April 2020: SAR Helicopter Loss of Control at Night: ATSB Report UPDATE 11 May 2020: European Search and Rescue (SAR) Competition Bonanza Aerossurance has extensive air safety, operations, airworthiness and tender / contract development experience. We are aviation advisor to one European Coast Guard agency. For practical aviation advice you can trust, contact us at: enquiries@aerossurance.com Follow us on LinkedIn and on Twitter @Aerossurance for our latest...
read moreRobinson R44 Power Loss: Excessive Lubricant
Robinson R44 Power Loss: Excessive Lubricant As the collective was raised during take-off on a post-maintenance check flight of Robinson R44 II Helicopter, N395CE, in Lake Hood, Anchorage, Alaska on 7 January 2016 “the [Lycoming IO-540 series] engine abruptly experienced a total loss of power. The helicopter remained on the ground and did not sustain damage. “ The National Transportation Safety Board (NTSB) say in their investigation report: …the purpose of the flight was to do a post maintenance check flight after servicing and overhaul of the helicopter’s fuel injection servo assembly. Disassembly inspection [on 14 January 2016] revealed large amounts of white contamination ranging in consistency from grease like to solid. The contamination was present in the manual mixture control valve, idle valve plate, fuel section O-rings, and the fuel diaphragm with the bleed port almost completely blocked. On 19 January 2016 safety investigators: …visited the facilities of Alaskan Aircraft Engines, Inc., in Anchorage [who had overhauled N395CE‘s fuel injection servo], and disassembled [another] recently overhauled fuel injection servo. The inspection revealed excessive amounts of a white grease like substance throughout the fuel injection servo, consistent with the servo removed from the accident helicopter. A representative from Alaskan Aircraft Engines stated that about 6 months prior they had switched assembly lubricants to Dupont Krytox an approved lubricant, but due to the investigation realized it was not being used in accordance with the maintenance manual and ended in excessive and inappropriate application. On 19 January 2016, the same day as the investigator’s visit: …Alaskan Aircraft Engines issued a Service Advisory that stated, in part: “Beginning in June of 2015 Alaskan Aircraft Engines purchased and began use of an approved assembly lube it had not used previously. This lube was used in excess and in locations not required by the manufacturer’s service manual. We believe this has the potential to cause a fuel distribution problem.” They also recalled affected components. The NTSB determined the probable cause of this incident on 12 December 2016 as: The overhaul facility’s improper and excessive use of an approved lubricant during overhaul of the fuel injection servo, which resulted in a disruption of fuel flow and a total loss of engine power. Another Accident (UPDATE 18 March 2017) We now know that an earlier accident had occurred on 16 December 2015 at Valdez, Alaska. R44 N255VS of Vertical Solutions LLC had been departing on a powerline survey for the Copper Valley Electric Association (CVEA). According to the NTSB report: After liftoff, the pilot hovered the helicopter about 10 ft above ground level (agl) before commencing a left turn, accelerating to about 25 knots, and initiating a climb. As the helicopter climbed through about 20 ft agl, the engine experienced a total loss of power. The pilot performed an autorotation, but the helicopter landed hard, resulting in substantial damage to the fuselage, skids and tail boom. Review of the accident helicopter’s maintenance records revealed that the fuel injection servo had been repaired and reinstalled about 2 hours before the accident flight. During postaccident examination of the fuel injection servo assembly, small amounts of a white, greasy substance were discovered in the servo assembly. The greasy substance, later identified as DuPont Krytox, is a lubricant used in small amounts and specific locations, during reassembly after overhaul or maintenance of the fuel injection servo assembly. The National Transportation...
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