For Rotors Grease is the Word
For Rotors Grease is the Word We look at two helicopter accidents (one fatal) where grease, and in particular the absence of grease, were critical factors. Case 1: AS355F1 N58020 15 September 2012, New Jersey (One Fatality) The National Transportation Safety Board (NTSB) report that, Airbus Helicopters AS355F1, N58020 operated by charter operator Analar Corporation was making a positioning flight to Atlantic City, NJ: During cruise flight, witnesses on the ground reported hearing a grinding or popping noise, which was followed by the separation of the yellow main rotor blade. In the NTSB Public Docket there is an eyewitness interview based report compiled using the innovative Immersive Witness Interview application from IWI. The pilot, the sole person on board, was killed. The NTSB go on: Examination of the fore/aft servo revealed that the internal threads of the upper rod end fitting on the servo were severely worn. The lower threaded portion of the upper rod end was not found secured into the servo’s upper end fitting and was not recovered. Additionally, the upper end fitting was packed with soil as the lower threaded portion of the upper rod end had separated from it prior to ground impact. A 100-hour maintenance inspection of the accident helicopter had been completed on the morning of the accident and a 600-hour inspection of the accident helicopter was completed about 3 months prior to the accident. Neither inspection detected the worn threads on the fore/aft servo upper end fitting. The operator used Mastinox, a corrosion inhibiting compound, during installation of the upper rod ends to the right-roll, left-roll, and fore/aft servos. The helicopter manufacturer’s maintenance manual listed only G.355 grease and did not prescribe for the use of Mastinox. However, the standard practices manual stated that a torque correction factor of 0.4 is used for G.355 grease, but not for Mastinox, since the latter is not a lubricant. The torque value listed in the manual for the rod ends already took a torque correction factor into account. A higher torque value would theoretically have been necessary when Mastinox was used in place of G.355 grease. The operator stated an adjusted torque value was not used during installation of the upper rod ends using Mastinox. Evidence of sealant at the junction of the upper rod end and nut, which was required to be applied during servo installation per the maintenance procedures, was not found on either the right-roll or left-roll servos. While the lack of sealant may not result in a catastrophic event, its breakage or absence (and/or radial play of a servo end bearing) noted during a maintenance inspection could be indicative of a loss of torque. Review of the helicopter manufacturer’s checklists and maintenance manuals revealed some guidance for servo inspections. The daily operating check (after the last flight of the day) included an instruction to check the main rotor servos for security and absence of leaks. The 600-hour inspection called for checking the radial play of the end bearings; however, there were no instructions to specifically check the threads of the servo end fitting or the torque of the rod end nut. The NTSB determined the probable cause to be: Disconnection of the upper rod end from the fore/aft servo due to severely worn threads, which resulted in a loss of control and separation of a main rotor blade during cruise...
read moreEASA Are On the Move! New EASA HQ
EASA Are On the Move! New EASA HQ The European Aviation Safety Agency (EASA) open for business on 6 June 2016 in a new office at: Konrad-Adenauer-Ufer 3 D-50668 Cologne, Germany The new building, in the shadow of the Dom, has the neoclassical frontage of a building originally built in 1913 as a railway headquarters. Other historical details, including some from the stairway and lobbies, have been preserved and refitted into the new building. It is owned by Commerz Real, who purchased the site for approx. EUR 128 million. The site is on a 20 year lease. The postal address and phone details remain unchanged. The new 21,400 m² HQ is on the opposite bank of the Rhine from the old Ottoplatz facility and is just north of the main station, the Köln Hauptbahnhof. Aerossurance will miss the ‘eccentric’ lifts in the main tower and the automated window blinds! Aerossurance’s Andy Evans is delighted to have been invited to present on Rotor and Transmission Safety at the 10th EASA Rotorcraft Symposium on 6th December 2016, the first to be held in the new EASA offices. Aerossurance has extensive air safety, airworthiness, operations, aviation regulation and accident analysis experience. For aviation advice you can trust, contact us at: enquiries@aerossurance.com Follow us on LinkedIn and on Twitter @Aerossurance for our latest...
read moreNTSB Report on C208B Caravan Ditching, Molokai, Hawaii, 2013
NTSB Report on C208B Caravan Ditching, Molokai, Hawaii, 2013 The US National Transportation Safety Board (NTSB) report on confusion over the applicable engine Instructions for Continued Airworthiness (ICA) and ditching procedures in a fatal 2013 accident in Hawaii. Cessna 208B Caravan N687MA, operated by Makani Kai Air, ditched off off Hawaii on 11 December 2013, after a sudden power loss. One passenger died in this accident (State Health Director Loretta Fuddy) and three people were seriously injured. As we reported previously, the accident and egress were filmed by passenger (Ferdinand Puentes). The NTSB report that: The flight departed from the Kalaupapa Airport on the island of Molokai, about 2 minutes prior to the accident, with an intended destination of the Honolulu International Airport on the island of Oahu. In a written statement, the pilot reported that shortly after takeoff from runway 05, at an altitude of about 400 feet above ground level (agl), he began a left turn for a downwind departure. Shortly after passing 500 feet agl, the pilot motioned toward the power lever to reduce power for the climb when he heard a loud “bang” followed by an immediate loss of engine power. The pilot continued the turn toward land, verified the fuel valves were on, and observed all engine gauges displaying “zero.” The pilot realized the airplane was not going to make it to land, and rolled the wings level while broadcasting a mayday distress call. Shortly after, the airplane landed within open ocean water in a flat or slightly nose up attitude. All the passengers and the pilot exited the airplane through the rear right door, and the airplane remained on the water surface for approximately 25 minutes before it sank. One passenger swam to shore, and United States Coast Guard and Maui Fire and Rescue helicopters recovered the pilot and 7 passengers from the water about 80 minutes after the ditching. Review of video taken by one of the passengers (which started with the airplane descending toward the water, showed the impact, and continued for about 15 minutes) indicated that the airplane impacted the water in a wings level, slightly nose-high attitude. The video showed that the airplane remained intact after contacting the water, and remained afloat throughout the video. VIDEO UPDATE 28 March 2019: A bizarre conspiracy theory that a frogman could be seen alongside the still alive Fuddy at 2m21s has been debunked in an equally bizarre video. Cessna note: After the aircraft sank but before it was recovered the wave action caused the aircraft to repeatedly contact the ocean floor. During that time the cabin was substantially damaged… Power Loss Examination of the Pratt and Whitney Canada (PWC) PT6A-114A engine revealed that “multiple compressor turbine (CT) blades were fractured and exhibited thermal damage”. Impact marks were found on the CT shroud consistent with the liberation of one or more of the CT blades. The NTSB believe the thermal damage, which precluded conclusive determination of the cause of the blades failures, was secondary and due to the engine fuel control unit increasing the fuel flow in response to the sudden loss of compressor speed when the blades failed. The NTSB say that about 18 months before the accident: …the engine had reached its manufacturer-recommended time between overhaul (TBO) of 3,600 hours; however, the operator obtained a factory-authorized, 200-hour TBO increase. Subsequently,...
read moreRotor Blade Tool Control FOD Incident
Rotor Blade Tool Control FOD Incident (Western Australia Police Air Wing Airbus AS365N3 VH-WPX) The Australian Transport Safety Bureau (ATSB) has just issued a report on an incident where a helicopter’s rotor blades were damaged during start up by Foreign Object Debris (FOD), namely a tool that had been left behind from earlier maintenance. The Incident Flight On 3 November 2015 Airbus Helicopters AS365N3 VH-WPX, operated by the Western Australia Police Air Wing, was undergoing maintenance check flights as part of Rotor Track and Balance (RTB) task at Jandakot Airport, WA. The helicopter had a Honeywell Chadwick Helmuth VXP Vibration Health Monitoring (VHM) system fitted. The day before the external diagnostics company that monitored the VXP data, advised the Air Wing of a rising vibration trend. In all three flights were made. After the third, two large gouges were spotted in the leading edge of one of the main rotor blades. The ATSB say: A spanner that had been used during the third track and balance related adjustments could not be located. It was later located on an adjacent taxiway about 43 m from the hangar. Due to the scuff marks and scratches found on the spanner, it was determined that it had been left in the rotor head area and was likely ejected during the aircraft start up. The pilot was aware that flight control maintenance had been conducted… The pilot signed the aircraft technical log and ‘accepted’ the aircraft prior to each of the three test flights. The pilot reported that the aircraft handled normally throughout the three test flights. The Maintenance History Two Licenced Aircraft Maintenance Engineers (LAMEs) were involved in the RTB adjustments. The operator’s Maintenance Organisation Manual (MOM) required that a work pack for maintenance tasks be created by the Maintenance Controller. LAME 1 explained to the ATSB that no work pack had been created for the task but they did annotate the ground run/test flight sheet and cross-referenced this in technical log. LAME 1 had tagged out a socket and a screwdriver. Prior to each test flight, LAME 1 placed the tools being used into a metal tray, and then placed the tray on top of the toolbox. As the job was on-going, there had been no documented requirement to place the tools back into their assigned location. LAME 1 had visually checked the tools in the metal tray prior to the third test flight, but did not use the [organisation’s] tag procedure [discussed below]. LAME 1 had performed adjustments to the main rotor pitch links and blade weights, and had asked LAME 2 to perform an independent inspection of the work after the second test flight. LAME 1 reported that the request had been for LAME 2 to both perform the independent inspection, and to check that no tools had been left on the helicopter. LAME 1 was not aware that the spanner that they had been using had been left on top of the main rotor blades. LAME 2 added: Stated that prior to the third test flight, they (LAME 2) had completed an independent inspection of the maintenance tasks, performed by LAME 1. LAME 2 did not notice that the spanner had been left on top of a main rotor blade. They noted that the blade was very flat, and that it would not be possible to see it on...
read moreUK AAIB: Boeing Safety Responses ‘Not Adequate’
UK AAIB: Boeing Safety Responses ‘Not Adequate’ Six months ago we published an article that discussed the UK Air Accidents Investigation Branch (AAIB) report into a serious incident involving a Boeing 747-443 G-VROM on 29 December 2014. AAIB has recently published an update on responses to their recommendations by Boeing. Two were classed ‘Not Adequate’, one ‘Partially Adequate’ and one ‘Adequate’. The AAIB was, we feel, generous in that last case! We look at the responses in more detail below. The Incident and Investigation After take-off the 747 developed hydraulic problems while retracting its landing gear. The required checklists were completed and the aircraft returned to land back at London Gatwick Airport. On approach, as the landing gear was extended, the right wing landing gear struck the gear door, preventing the gear leg from fully deploying, after a go-around and troubleshooting, landing on the three remaining main gear was successfully competed. This also resulted in 5kg ‘strike board’ becoming detached and falling into a field in Kent. On investigation it was found that an 85 kg actuator that had been changed the day before due to a leak. The Boeing Aircraft Maintenance Manual (AMM) did reference the part number for a sling to use with a hoist but gave no instruction on how to use it. Instead AAIB say: The team…manhandled the actuator between the two technicians standing in the lifter and the engineer standing on the steps. The weight of the actuator was then supported by the two technicians, while the engineer attempted to install the pin which secured the actuator to the hanger. …the task became so physically demanding that the maintenance team became entirely focused on just attaching the actuator to the aircraft, in order to relieve themselves of the 85 kg weight they had manually supported for over 30 minutes. As such, they had no remaining capacity to ensure they installed the actuator in the correct orientation. It was subsequently determined that they had rotated it 180° about its long axis during installation, effectively installing it upside down. The AAIB note that: …the design of the actuator itself increased the probability of the error remaining undetected. The actuator was virtually uniform in shape and colour, such that there was no obvious top or bottom to it. The structural connections could be installed in either orientation and the use of flexible hoses meant the hydraulic connections could be made to fit an incorrectly installed actuator. Finally, the hydraulic port on the bottom of the actuator was labelled ‘UP’, with the one on the top labelled ‘DN’, which was inherently open to misinterpretation. These markings relate to the movement of the gear not the orientation of the actuator. The AMM also did not require a functional test either, so the error was not detected. The operator conducted what the AAIB praised as “a detailed investigation”, culminating in a “comprehensive” report with 28 recommendations, which they openly shared with the AAIB. The majority of these related to internal improvements in process, but a number also related to possible improvements in the aircraft manufacturer’s documentation to remove ambiguity. While, the specific investigation methodology used by the operator is not discussed this sounds like the sort of suite of improvement actions you might expect a diligent organisation to identify, using an approach similar to Boeing’s own Maintenance Error Decision Aid (MEDA). MEDA is a tool developed over 20 years ago...
read morePilatus PC-24 Drops into EBACE
Pilatus PC-24 Drops into EBACE As the first prototype, P01, drops into the European Business Aviation Conference and Exhibition (EBACE) in Geneva for a day, AW&ST report that: PC-24 Prototypes Are Keeping Busy: The first aircraft, P01, is appearing at the show before flying to Spain for high-speed testing, while P02 has flown to the U.S. There it will undergo autopilot trials with Honeywell in Phoenix, and cold-soak tests in the chamber at Eglin Air Force Base in Florida. It will return to Switzerland toward the end of the year. A third, production-standard aircraft will make its first flight before the end of this year. As we previously reported, at EBACE 2014 the company took non-refundable deposits for 84 aircraft and sold out all 2017-2019 production slots. The order book will not be reopened until the NBAA show in Oct 2017, just prior to certification. AINOnline report that since P01 made its maiden flight on 11 May 2015: With just over 500 flight hours logged by two prototypes, and with a third due to join the campaign towards the end of 2016, the highly versatile mid-light twinjet is not quite a quarter of the way towards completing type certification, scheduled for around the end of 2017. The PC-24 is an intriguing new aircraft. It’s a twin engine business jet priced at $8.9 million (in 2017 dollars). It can seat 6-8 in business configuration and up to 10 in high density seating. But it is more than just another business jet. The PC-24’s unique selling point is mission flexibility. It has with good field performance and a modest 81kt stall speed, capable of operating from 2,690ft / 820m strips, with a unpaved strip capability, giving access to 12,0o0 paved and 9,000 unpaved strips according to Pilatus. It has a pallet-sized 51x49in / 1.30×1.25m PC-12 style cargo door and a flat-floor 501ft³ / 14.2m³ cabin, ideal for cargo, medevac missions and installing special mission equipment. Aerossurance is convinced this is a versatile aircraft type that will make its mark in the oil & gas and mining sectors (among others). The PC-24’s Advanced Cockpit Environment (ACE™) avionics suite was developed by Pilatus in partnership with Honeywell. The aircraft has a Max Take Off Weight of 17,650lb / 8,005kg and a maximum payload of 2,500lb / 1,135kg. With full fuel the payload is 915lb/ 415kg. It has a range of 1,950nm / 3610km flown single pilot with 4 passengers (NBAA IFR reserves, 100-nm alternate). Powered by two Williams FJ 44-4A engines with a max take-off thrust of 3,400lbf each, high-speed cruise speed is 425kts at 30,000ft. UPDATE 19 July 2016: Pilatus Business Aircraft has broke ground on a new 10,900m² facility at Rocky Mountain Metropolitan Airport, Broomfield, CO (its US home since 1996) on 14 July 2016. The facility, due to open in spring 2018, will become the centre for Pilatus’ completions, sales and support activities in the Americas. It is reported that: The facility was sized to accommodate an increase in employment and completions work as Pilatus brings its new PC-24 light jet to market, Pilatus said. The company expects to hire 60 more people, in addition to the 80 already at Broomfield, as it ramps up full production of the jet by 2020. Tom Aniello, VP of Marketing for Pilatus North America says the first eight PC-24s will be completed in Switzerland. He says: After that, only aircraft to be delivered in North and South America will be completed in...
read moreUKMFTS Rotary Wing Aircraft Service Provision Contract Awarded
UK Military Flying Training System Rotary Wing Aircraft Service Provision Contract Awarded In the second major UK Military Flying Training System (UKMFTS) contract award this year, Airbus Helicopters has won the contract to provide training helicopters for the RAF, Royal Navy and Army Air Corps until 2033. Airbus will supply and maintain 29 H135s (to be given the UK military name Juno) and three larger H145s (to be given the name Jupiter). These will deliver up to 28,000 flying hours per annum. The £500mn Rotary Wing (RW) Aircraft Service Provision (ASP) contract was placed by Babcock / Lockheed Martin joint venture Ascent Flight Training. Ascent, selected as the UK MOD’s flying training partner in 2008, were themselves awarded a £1.1 billion contract by UK MOD as prime contractor, which includes provision of infrastructure, simulators, training design and instructors, as well as sub-contracting the aircraft provision. Initial Course Capability is expected in Quarter 2 2018 with a mix of civil (Ascent) and military instructors. Ascent will deliver basic and advanced rotary wing training at RAF Shawbury and Army Air Corps Middle Wallop, with the H135 Juno. Pilots selected for training in mountain and maritime helicopter operations will receive instruction at RAF Valley on the H145 Jupiter. Fewer H145s are needed than the current B412 fleet as primary UK SAR operations are now contractorised under an HM Coastguard contract. Both the H135 and H145 are twin-engined helicopter types. Apart from a few Army Gazelles their are no single engine helicopters in front line UK military service. UPDATE 8 December 2016: Full service training delivery is now due to begin on 1 April 2018, an auspicious date given it is the 100th Anniversary of the foundation of the RAF. UKMFTS H135 Juno Turbomeca Arrius 2B2+ turboshafts have been selected to power the H135 Junos rather than the rival Pratt & Whitney Canada PW206Bs. UPDATE 22 June 2016: Craig Hoyle reports that the first H135 Juno for UKMFTS (MSN 2001, D-HECZ) was just about to conduct its first ground run: UK’s first military H135 ready for ground test The first flight was due in mid July 2016. The rapid progress was due to Airbus Helicopters committing to build prior to contract. One aircraft will be shipped to Airbus UK in Oxford for mission modifications which will include a cargo hook and a defensive aids suite emulator. UPDATE 29 July 2016: The first UKMFTS H135 has flown. UPDATE 8 December 2016: The first H135 Juno, to be G-CJIW (before being military registered), has arrived in the UK (though it is not currently shown on the CAA registration database and was delivered as D-HECV). UKMFTS H145 Jupiter Turbomeca is the sole engine supplier on the H145 Jupiter with the Arriel 2E. The H145 Jupiters will have emergency flotation systems and hoists. UPDATE 21 November 2016: The first H145 Jupiter, G-CJIV (formerly D-HADT), was put on the UK civil register on 11 November 2016 and has been delivered to the Airbus Helicopters UK site at Oxford for mission equipment fitment prior to delivery in Q1 2017. UPDATE 3 April 2017: One H145 Jupiter and two H135 Junos have been delivered to RAF Shawbury. UPDATE 5 April 2017: Two more of each type are in modification at Airbus UK in Oxford. Contract Award Comment Paul Livingston, Managing Director of Ascent Flight training said: We were left in no doubt that Airbus Helicopters competitive offer was the best choice for the rotary wing element of UKMFTS. I have high expectations of...
read moreOffshore Helicopter Safety Performance: 2016 HeliOffshore Conference Report
HeliOffshore 2016 Conference Report: Offshore Helicopter Safety Performance The offshore helicopter safety association, HeliOffshore, has launched a new ‘Safety Performance Model’ and Safety Strategy for the industry. These were agreed at its second conference and AGM in Prague, 13-15 May 2016. They are the basis for both an on-going root and branch review of safety in the sector and collaborative safety improvement. The HeliOffshore conference was attended by 180 leaders from operators, helicopter manufacturers, oil and gas companies, regulators, suppliers and service providers (including Aerossurance). Introduction: Collaboration, Commitment and Courage In her opening remarks HeliOffshore CEO Gretchin Haskins quoted President John F Kennedy: “The problems of the world cannot possibly be solved by skeptics or cynics whose horizons are limited by the obvious realities“, and how he went on to say we need people with vision “who can dream of things that never were and ask “why not?”“. HeliOffshore, founded by the 5 largest players in offshore helicopter operations (Babcock, Bristow, CHC, ERA and PHI), has grown to almost 90 members all committed to collaborating to improve offshore helicopter safety. Haskins outlined the group’s ambitious aim: Our aim is that no lives are lost due to offshore helicopter transport. Agreements at this conference – and work already underway to share information and expertise across the industry – will help to achieve that. In light of a recent tragic accident in Norway, Haskins said, in a subsequent interview with Flight International: Although “in retrospect, every accident is preventable” she admits “if it was easy, it would have been done already”. That reminds us of another JFK quote about choosing ambitious goals: “…not because they are easy, but because they are hard; because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one we intend to win…” The key, she says, is to build “system resilience” and “increased survivability” in case of an equipment malfunction. The entire industry – from OEMs, to operators, to oil and gas customers – must also work proactively to increase safety, she says. As part of the introduction a video message from BP‘s Chief Executive Upstream Bernard Looney discussing the 2009 G-REDU and G-REDL accidents and the critical importance of safety to the oil and gas industry. He then then introduced pilots and engineers from HeliOffshore operators worldwide, who are collaborating on safety for their vital perspective: https://www.youtube.com/watch?feature=player_detailpage&v=G60td-ZEpkI In addition to Commitment and Collaboration, HeliOffshore’s Operations Director Francois Lassale, mentioned another key component: Courage. HeliOffshore Safety Strategy: Sprinting a Marathon Bill Chiles, Chairman of the HeliOffshore Board, reflected that he had always seen HeliOffshore as being engaged in a long term marathon, but that recent events show that the industry and its stakeholders must accelerate to a sprint. Chiles explains how at the conference: Members have adopted a plan to undertake a fundamental review that will enhance the reliability and resilience of the offshore fleet and the systems that support it – both human and machine. The Safety Performance Model, inspired by the Flight Safety Foundation (FSF) Basic Aviation Risk Standard for Offshore Helicopter Operations (BARS OHO) bow-tie presented at the 2015 conference (which we discussed last year). The prioritisation has been influenced by the EASA Safety Risk Portfolio for Offshore Helicopters. UPDATE 1 February 2017: BARSOHO Version 3, fully aligned with the HeliOffshore SPM, is issued and...
read moreValuJet Flight 592: 11 May 1996
ValuJet Flight 592: 11 May 1996 On 11 May 1996 a ValuJet DC-9-32 N904VJ crashed in flames into the Florida Everglades while trying to return to Miami, killing all 110 occupants. ValuJet was an Atlanta, Georgia based low cost carrier which started operations 26 October 1993. ValuJet Flight 592 was a scheduled flight from Miami (MIA) to Atlanta (ATL). The DC-9 was also carrying a small amount of cargo, including mail and ‘company-owned material’ (COMAT). The COMAT was items being returned to the airline in Atlanta by SabreTech, a sub-contracted maintenance organisation in Miami. It consisted of three tyres and wheels, and five boxes of cabin emergency oxygen generators, labeled as “Oxy Cannisters – ‘Empty’”, stored in the forward Class D Cargo Compartment. Seven minutes after take-off the crew identified there was an aircraft fire, but although they attempted to return to MIA, just over 2 minutes later the aircraft impacted the ground. The Investigation During wreckage recovery from the swamp it became evident that there had been an intense fire in the forward cargo compartment. During the investigation the NTSB discovered that the 5 boxes of chemical oxygen generators contained more than 100 time expired, but still active, oxygen generators. They say: The expired oxygen generators had been removed from three ValuJet MD-80 aircraft undergoing maintenance at SabreTech. The Board’s investigation revealed that, although many of the SabreTech mechanics who removed the generators understood the danger they could pose, the generators were nevertheless delivered to SabreTech’s shipping and receiving department without communicating what the items were, or that they were hazardous. Rather than dispose of the generators properly or at least fit them with safety caps designed to prevent their accidental activation, they were boxed up and sent to ValuJet in order to clean up the maintenance area in preparation for a visit by a prospective customer. In addition, they were incorrectly labelled… The NTSB determined that one or more of the oxygen generators activated. This created both the heat (as a by-product of the chemical reaction) and the oxygen to initiating a fire (fuelled by the tyres) that eventually brought the aircraft down. The NTSB concluded that: …the lack of a formal system in SabreTech’s shipping and receiving department, including procedures for tracking the handling and disposition of hazardous materials, contributed to the improper transportation of the generators aboard flight 592. ValuJet did not adequately oversee SabreTech: Had it ensured that SabreTech’s employees were trained on the company’s lack of authority to transport hazardous materials and had received hazardous materials recognition training, SabreTech might not have mishandled the packaging and shipment of the oxygen generators. In their investigation report the US National Transportation Safety Board (NTSB) determined that: …the probable causes of the accident, which resulted from a fire in the airplane’s class D cargo compartment that was initiated by the actuation of one or more oxygen generators being improperly carried as cargo, were: (1) the failure of SabreTech to properly prepare, package, and identify unexpected chemical oxygen generators before presenting them to ValuJet for carriage; (2) the failure of ValuJet to properly oversee its contract maintenance program to ensure compliance with maintenance, maintenance training, and hazardous materials requirements and practices; and (3) the failure of the Federal Aviation Administration (FAA) to require smoke detection and fire suppression systems in class D cargo compartments. Contributing to the accident was the failure of...
read moreBell 412 Cross Tube Failure Case Study
Bell 412 Cross Tube Failure Case Study Earlier this year the German accident investigation agency, the BFU, published their report into Helicopter Emergency Medical Service (HEMS) Bell 412HP that suffered a rear cross tube failure during start up at a hospital in Berlin on 6 September 2010. The helicopter was fitted with ‘high’ skids manufactured by Aeronautical Accessories Inc (AAI) and certified under Supplementary Type Certificate (STC) SR01052AT. The skids are supported by forward and after cross tubes. The rear cross tube is mounted to the underside of the fuselage by way of a single central bracket made of two ‘half shells’ (the earlier Bell 205 and Bell 212 had two attachment points). The high aft cross tube was fractured on the right edge of the half shell. The fractured cross tube damaged the right fuselage bottom side. The damaged tail boom rested on the filling station [sic i.e. the helideck fuel facility] and the wall of the landing platform behind the helicopter. …the area of the two half shells is more rigid than the rest of the [cross tube] pipe resulting in change of stiffness at the ends. Furthermore,…where the U-bolts clamp the half shells…a rigid clamping situation exists. Therefore, the area of the half shells is to be viewed as a highly stressed area… During the manufacturing process the [cross tube] pipe which is made of a high-strength aluminium alloy is shot blasted [i.e. shot peened]. The fatigue life of material shall be increased by shot blasting inserting residual compressive stress. The rear cross tube had first been installed new (on another helicopter) ten years earlier. On the day of the accident the [rear] cross tube had 6,245:08 flight hours and 17,690 flight cycles. After the last inspection [in May 2008] 1,410:34 hours and 4,120 cycles [landings]. In 2007 at the same operator a fracture of an aft cross tube occurred with an identical landing skid. The fracture surface was almost identical with the one of 2010. The cross tube of 2007 had 3,820 flight hours and 10,732 cycles. At that time the US Federal Aviation Administration (FAA) reported in a Special Airworthiness Information Bulletin that: Three reports from the field of failed aft crosstubes have been reported to AAI. Two of those failures occurred during landing. The other failure occurred during transport of the aircraft on ground handling platform equipment. Also, in one case during landing, the aft crosstube failed and subsequently the front cross tube failed causing the helicopter to lean severely on the failed right skid One was the 2007 German case. The other two involved failures at 11894 and 15336 cycles. In the 2010 Berlin case, laboratory analysis confirmed a facture propagated by fatigue with final failure by overload. There was no evidence of a hard landing. After the initial failures: In April 2008 Aeronautical Accessories published the Alert Service Bulletin (ASB) No. AA-07109 because of the incidents with the high aft cross tube. The Bulletin stipulated the operating limitations for the cross tube to be 20,000 cycles. Various inspections for crack detection on the surface of the cross tube and detection of permanent deformations were described… Essentially these are to check the pipe surface for crack development. During these checks the areas of the central half shells, which have failed verifiably at least twice, were omitted. BFU Analysis The BFU is of the opinion that...
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