Canadian B212 Crash: A Defective Production Process
Canadian B212 Crash: A Defective Production Process (Yellowhead Helicopters C-GYHQ, Alberta) On 28 June 2021, Yellowhead Helicopters Bell 212 C-GYHQ was destroyed when it broke up in-flight while supporting fire fighting operations near Evansburg, Alberta. The pilot, the sole occupant was killed. The Transportation Safety Board of Canada (TSB) explain in their safety investigation report, issued 7 September 2022, that… …as the helicopter was approaching the landing area to pick up the final group of fire fighters, one of the main rotor blades separated from the rotor head assembly. The second rotor blade and rotor head assembly then broke free from the helicopter and the helicopter crashed. Investigators observed that the main rotor hub strap retaining pin of blade A had failed. TSB say that just eight days earlier… …both main rotor hub straps and the associated retaining pins had been replaced with new parts acquired from Bell. This work was completed to comply with the requirement to replace the parts after 1200 flight hours or 24 months. On 22 June 2021, a local post-maintenance test flight was conducted. No defects were noted. Between 22 and 27 June 2021, the occurrence helicopter accrued 18.9 flight hours. The main rotor hub strap retaining pins had accrued approximately 21.4 hours time in service at the time of the occurrence. The investigators go on to explain that significantly: Metallurgical analysis of the 4 pins (part number 204-012-104-005) revealed that the failed pin (serial number FNFS90, bottom of figure below) was manufactured from 316 stainless steel, whereas the other 3 pins (serial numbers FNFS49, FNFS54, and FNFS75) were manufactured from H11 tool steel. Bell sub-contracted the manufacture of main rotor hub strap retaining pins to 3 suppliers. All 4 retaining pins installed on the occurrence helicopter were manufactured by Fore Machine Company (FMC). As FMC held no FAA approval, nor was it required to be. The manufacture of the pins at FMC was subject to a first article inspection process, conducted for Bell by a third-party using personnel trained and approved by Bell, before ultimately being released by bell.. Bell conducts oversight of its suppliers and audited FMC at their Haltom City, Texas facility in Forth Worth in 2016, 2017, and 2019. Bell’s last audit of FMC before the occurrence pins were manufactured (in 2018) was completed on 17 August 2017 and covered Appendix I: Special Requirements for Offload of Bell Planning Operations, and Appendix VI: “Controlled Item Program” Supplier Requirements of Bell’s Supplier Quality Requirements Manual. This audit resulted in 2 findings, one related to FMC’s documentation control procedures, and the other related to measurement section analysis. Additional Bell personnel would generally visit FMC facilities… …on an average of 1 to 3 times a month for various reasons, including completing source inspections, reviewing non-conformances…and verifying, validating, and rectifying defects. During site visits, Bell personnel would regularly walk through the stores area to ensure that the area was orderly and that raw material was correctly identified and tagged. These oversight activities and site visits did not result in any significant observations or recommendations… The FAA audits Bell’s vendor audits and supplier oversight. The last FAA audit of Bell/FMC, was conducted on 1 May 2018. Remarkably (emphasis added) the TSB… …determined that, when the occurrence pins were manufactured in the fall of 2018, FMC stored the raw material in its stores area by material diameter, not by...
read moreSheriff Super Puma Brownout Accident: NTSB Report
Sheriff Super Puma Brownout Accident: NTSB Report (LASD AS332L1 N950SG) On 19 March 2022, Airbus AS332L1 Super Puma N950SG of the Los Angeles County Sheriff Department (LASD) was destroyed in a brownout landing accident near Azusa, California. Four occupants received serious injuries, and the other two escaped with minor injuries. The aircraft came to rest at a cliff edge. News Report VIDEO. In the short US National Transportation Safety Board (NTSB) safety investigation report, issued on 9 September 2022 and the associated public docket it is explained that the police helicopter, callsign Air Rescue 5, had been tasked to conduct a HEMS / air ambulance flight to transfer a patient from a road accident in a canyon in the Angeles National Forest. Oddly in the accident report form the LASD did not declare the applicable regulations a being ‘Public Aircraft’ but incorrectly as a ‘Part 91 Air Ambulance Flight’ The aircraft commander had 5,382 hours experience, 1243 on type. The co-pilot had 2,686 hours experience, 297 on type. There were also a crew chief (hoist operators), two medics and a UCLA doctor onboard. The initial plan had been to land on the main road itself, but the space was filled by vehicles unable to progress due to the road accident. The crew then decided to land in an unmetalled turnout (or a dirt passing area) and conducted at least two low recce passes. The crew chief (CC) called out a ‘stinger’ (tree) obstacle that the aircraft commander (PIC) acknowledged. In their interview with the CC: The CC stated that the PIC said that he was going to stay close to the roadway in case they get into some brownout. The CC stated that he thought the PIC was ready for a brown out situation. The CC stated that they started the approach and were kind of coming in a sideways angle facing the south toward the tree. He said the dirt wasn’t too bad and about 7 to 10 feet above the ground. He still had visibility and was in the process of clearing the rotors and the tail. He said that the called those out (rotors and tail clear). The aircraft commander was maintaining the adjacent asphalt road as a reference through the cockpit bubble window. [The CC] looked out toward the ground and noticed that they were drifting forward. He said, “Scotty you’re drifting forward, hold.” He said that they were continuing to move so he said it again, “Scotty you’re drifting forward, hold, I need you to hold right here.” He said that they continued to drift, and he called out the tree at 12 o’clock. He said that it felt like they climbed a little bit, and that he could clearly see the blades moving toward the trees, then everything happened right after that. The aircraft came to rest on its left side. The crew chief was thrown clear of the fuselage but restrained by his crew harness. Accident site VIDEO. The PIC (Pilot Flying) told the NTSB he had been aware of the brownout risk and: They started the approach, and the PIC called out that he still had visual reference to the road. While about 5 feet above the ground, he heard one of the crew in the back call “hold.” The crew chief didn’t elaborate, he just said “hold.” The PIC placed the helicopter into a...
read moreGarbage Pilot Becomes Electric Hooker
Garbage HESLO Pilot Becomes Electric Powerline Hooker (Helitrans AS350B3 LN-OGA) On 16 October 2021, Helitrans Airbus AS350B3 LN-OGA was tasked with moving large bags of rubbish as a Helicopter External Sling Load Operation (HESLO) in the Lofoten archipelago in Northern Norway. During a positioning sector the underslung load line cut three low voltage power lines. The Accident Flight The Norwegian Safety Investigation Authority (NSIA) explain in their safety investigation report (issued in Norwegian only on 30 August 2022) that the local waste management company had gathered rubbish at 15 waterfront locations which need transfer to 6 landfill sites. The task was estimated to take two days. It had been delayed by weather and only started on 15 October 2022 when 13 lifts were performed, carrying 3-6 bags on each. The pilot, who had 1,282 hours of flight experience, had spent a couple of hours planning the evening before using iPad application Air Nav Pro, maps and satellite data. It was not possible to do a ground recce at all the sites. At 10:00 on 16 October 2022 the helicopter again left Leknes Airport with the pilot, a load master and an employee of the waste company. The weather was better than the previous day, with good visibility and 10–15 knots south-easterly wind. At the collection point, the loader and the customer’s representative left the helicopter, and the pilot began the flight by transporting the large bags to the predefined landfill at Banhammaren, at the southern tip of Mortsund. The flight route to the landfill was south of Mortsundholmen and the last part of the approach to Banhammaren was made from the south. At the landfill site the pilot could released the load by electrically activating a hook at the lower end of the 15 m long line. Three round trips were required to move 11 bags of rubbish. On the first two return sectors the pilot flew back the route they had flown outbound, south of Mortsundholmen. After the third load was delivered the helicopter needed to pick up the ground party and head to the next collection point. On this return flight the pilot choose to fly down the centre of a narrow strait between Mortsundholmen and Mortsund. Unbeknown to the pilot there were three 5.6 mm 230V powerlines across this strait at amount 55 feet (below the then 100 feet threshold for reporting aviation obstacles). On the way through the strait, the commander spotted a power line pole on the north side of the strait and looked down through the helicopter’s floor window. In the window he saw three power lines…. Soon after, he felt a jerk… The captain quickly realized that the cargo line had caught in the power line and immediately opened the helicopter’s cargo hook with the electric release mechanism. The cargo line was disconnected and fell into the sea without causing any damage to property or people [it was later recovered by divers]. The NSIA note that a October 2020 regulation change in Norway will require obstacles >50 feet to be reported by July 2025. NSIA Analysis NSIA were complementary about the pilot’s planning, but note that the mapping data naturally did not show the cables as they were not, nor needed to be, reported. The decision to make the last departure across the strait between Mortsundholmen and Mortsund therefore becomes incomprehensible. The pilot suggested that contributing factor to that choice of route “may have been that he had a different focus when the...
read moreR66 Loss of Control Investigation Hampered by Lack of Cockpit Video
Robinson R66 LOC-I Investigation Hampered by Lack of Cockpit Video (N450MC) On 9 January 2020 at c20:29 Local Time privately owned Robinson R66 N450MC was destroyed in an accident near Mechanicsburg, Pennsylvania. The pilot and passenger both died. The US National Transportation Safety Board (NTSB) safety investigation report, issued 28 June 2022, explains that: The helicopter pilot was conducting a night cross-country flight in visual meteorological conditions. The pilot was 58 and had just over 2000 hours experience, 167 on type. The pilot attended a [Roninson] safety course in February 2019 for the R66. At that time, the pilot had not accumulated any hours in the R66. …the instructor indicated that the pilot had “very good control” of the helicopter when performing normal and emergency procedures and that he was “very comfortable practicing the [autorotations].” The instructor suggested that the pilot obtain more training on emergency procedures. The pilot was rated “average” on all demonstrated maneuvers. Investigators report that: Recorded data showed that while the helicopter was flying at an altitude of about 2,300 ft mean sea level and at an indicated airspeed of about 107 knots, slight pitch and roll oscillations occurred for about 20 seconds followed by a left roll that continued until the helicopter was inverted. A main rotor blade contacted the tailboom, leading to an in-flight breakup over a residential area. NTSB Safety Investigation Pitch and roll hardly changed before the in-flight upset, so the investigators concluded that the autopilot was mostly likely engaged when the pitch and roll oscillations started. The oscillations could have been the result of: the autopilot reacting to an external disturbance (moderate-to-severe turbulence was reported in the area) pilot control inputs in-flight malfunction of the autopilot’s roll servo actuator The investigators say: While any of these scenarios might have precipitated the initial oscillations, none would have precluded the pilot from overriding the autopilot and manually flying the helicopter. The helicopter was equipped with devices that recorded flight and engine data at a rate of at least one parameter every second. However, the lack of an on-board crash-resistant cockpit imaging system hampered the investigators ability to reach a conclusion. NTSB has issued a safety recommendation install crash-resistant flight recorders with cockpit imaging systems for existing helicopters. Robinson responded that… …it incorporated a cockpit camera system as standard equipment on all similar model helicopters manufactured beginning the year after the accident and offered as a kit for existing helicopters the same year. However, those camera systems were not crash-resistant. During 2001 and 2009, the pilot was diagnosed with obstructive sleep apnea and coronary artery disease, respectively. The pilot was using a continuous positive airway pressure (CPAP) device for the sleep apnea “with good adherence and symptom control”. The heart problem was assessed as a “mild-to-moderate” and “did not require stenting or surgery”. The pilot did not show the typical symptoms of heart failure. Small quantities of clonazepam and ethanol were found during toxicology testing but NTSB were not able to determine if these were relevant. Overall the NTSB concluded that: [No] operational evidence indicated that the pilot’s performance was deficient during the flight time preceding the oscillations. Investigators make no comment on the possibility of disorientation during a night VMC flight. NTSB Probable Cause A severe left roll excursion after the onset of pitch and roll oscillations, which were not arrested...
read moreFenestron Failure EC130B4 Hawaii
Fenestron Failure EC130B4 Hawaii (N11QK, Blue Hawaiian Helicopters) On 5 March 2020 Airbus EC130B4 N11QK, of Blue Hawaiian Helicopters, was damaged in an accident near Kalapana, Hawaii, during a Part 135 air tour flight. Two passengers suffered minor injuries, the pilot and three other passengers were unharmed. The Accident Flight The US National Transportation Safety Board (NTSB) explain in their safety investigation report, released 16 August 2022, that the second of a pair of helicopters that had departed Hilo International Airport heading for an area known as the ‘Old Ocean Entry‘, a lava flow. As the helicopter passed over the shoreline, the pilot [7878 hours total, 1969 on type] noticed a significant, high frequency airframe vibration. He said that as soon as the vibration started, the tail rotor chip annunciator light briefly illuminated, and as the vibration continued, the tail rotor chip light “flickered.” The vibration and noise stopped after a few seconds and the chip light extinguished. The pilot selected a large open area as a precautionary landing site and slowed the helicopter on the approach. As the helicopter slowed, he raised the collective, and applied right tail rotor pedal, but the nose of the helicopter veered to the left. The pilot noted that he eventually applied full right tail rotor pedal, but the nose of the helicopter continued to the left. About 200 feet above ground level, with the right tail rotor pedal fully depressed, the helicopter began to spin to the left. To stop the spin, he attempted to gain forward airspeed but eventually closed the engine throttle and preformed a hovering [sic] autorotation. He stated that the helicopter descended, touched down hard, and subsequently rolled onto its right side, sustaining substantial damage to the fuselage, tail boom, and the main rotor drive system. The NTSB Safety Investigation One of the 10 fenestron blades had been released at the blade root, where the blade’s drain port is situated. The released part of the blade was found in the fenestron outer fairing. The fracture surface was flat starting at the aft end of the blade, up until about two-thirds of the distance to the leading edge, while the forward section exhibited shear lips. Examination of the fracture surface infected that… …the failure initiated from two separate origin areas, one on either side of the drain hole at or near its intersection with the aft rib face and grew progressively along the blade chord through about 60% of the blade before fracturing in overstress. The origin areas had been damaged with no identifiable features. Further from the origin, variable-spaced fatigue striations were observed, consistent with high cycle fatigue crack growth. The blade exhibited some geometric anomalies, its rib thickness was measured at 1.27-1.70 mm and the drain hole offset measured 0.23 mm. The acceptable engineering limit specified on the technical drawing was 2.3±0.3mm and ±0.2 mm respectively. Three other blades from N11QK were found to have fatigue cracks aligned with the blade drain hole on the suction side of the blade. Airbus Helicopters performed a root cause analysis that identified various potential factors that could contribute to the crack development. The two that were judged to be the main contributors were water drain hole geometry and rib thickness. Additionally predictions during design underestimated blade loads and it has since been shown that more sideslip manoeuvres occur in service that anticipated. Airbus Helicopters issued Alert Service Bulletin No. EC130-05A033 on 10 August 2020 to provide instructions to inspect blades at the drain hole section and establish replacement criteria. ...
read moreHow One Missing Washer Burnt Out a Boeing 737
How One Missing Washer Burnt Out a B737-800 (China Airlines B-18616) On 20 August 2007, shortly after parking on stand at Okinawa-Naha Airport, China Airlines Boeing 737-809 B-18616 suffered a massive fuel leak which ignited. After all 165 persons on board had evacuated, a large explosion occurred in the centre of the aircraft, which burned out completely. Investigators determined this occurred because one washer had fallen off before a nut was attached. The Japan Transport Safety Board (JTSB) safety investigation report explains that it is “highly probable” that: When the Aircraft retracted the slats after landing at Naha Airport, the track can that housed the inboard main track of the No. 5 slat on the right wing was punctured, creating a hole. Fuel leaked out through the hole, reaching the outside of the wing. A fire started when the leaked fuel came into contact with high-temperature areas on the right engine after the Aircraft stopped in its assigned spot, and the Aircraft burned out after several explosions. The reason the slat track was punctured was… …that the downstop assembly having detached from the aft end of the above-mentioned inboard main track fell off into the track can, and when the slat was retracted, the assembly was pressed by the track against the track can and punctured it. The downstop assembly detached because it was… …highly probable that during the maintenance…on the downstop assembly about 1.5 months prior…the washer on the nut side of the assembly fell off, following which the downstop on the nut side of the assembly fell off and then the downstop assembly eventually fell off the track. It is considered highly probable that a factor contributing to the detachment…was the design of the downstop assembly, which was unable to prevent the assembly from falling off if the washer is not installed. Unusually the nut was smaller diameter than the hole the bolt passed through. Despite the fact that the nut was in a location difficult to access during the maintenance works, neither Boeing nor China Airlines had paid sufficient attention to this when preparing the Service Letter and Engineering Order job card, respectively. Also, neither the maintenance operator nor the job supervisor reported the difficulty of the job… There is an excellent short video that illustrates this accident: Flight Safety Australia: It was almost all over: the destruction of China Airlines flight 120 Safety Resources You may also find these Aerossurance articles of interest: B1900D Emergency Landing: Maintenance Standards & Practices Fuel Tube Installation Trouble Fire After O-Ring Nipped on Installation Uncontained CFM56-7 Failures: Southwest B737-700s Uncontained PW1524G Failure During CS100 Certification Testing Machining Defect Cause of V2500 Failure B787 GEnx Fan Shaft Failure USAF Engine Shop in “Disarray” with a “Method of the Madness”: F-16CM Engine Fire Bell 407 Rolls-Royce 250-C47B Uncontained Engine Failure after Bearing Failure NTSB Confirms United Airlines Maintenance Error After 12 Years Machining Defect Cause of V2500 Failure ‘Aggressive’ Grit Blasting Maintenance Leads to Engine Fire & IFSD Micro FOD: Cessna 208B Grand Caravan Engine Failure & Forced Landing Cessna 208 Forced Landing: Engine Failure Due To Re-Assembly Error NDI Process Failures Preceded B777 PW4077 Engine FBO King Air 100 Uncontained TPE331-6 Failure – Inappropriate Repair Scheme B767 Fire and Uncommanded Evacuation After Lockwire Omitted Engine Life Limit Exceedance Caused Logging Helicopter Fatal Accident Engine Failure after Inadvertently Being Put Back into Service Incomplete Coking...
read moreSecond Time Unlucky: Fatal Greek Wirestrike High-Wire Illusion
Second Time Unlucky: Fatal Greek Wirestrike High-Wire Illusion (iFly Leonardo A109C SX-HTO) On 20 August 2019 Leonardo A109C SX-HTO, operated by iFly, crashed into the sea after striking electric powerlines off Poros Island, Greece moments after take off from a helipad at Galatas. The pilot and both passengers were killed. On approach, unbeknownst to the pilot, he had passed under the cables. The Accident Flight The Greek Air Accident Investigation and Aviation Safety Board (AAIASB) issued their safety investigation report in June 2022. They explain that the helicopter was due to make a multi-sector flight, with an an unlicensed landing site at Galatas being the first stop. iFly’s Operations Manual Part C stated that a high and low reconnaissance should normally be conducted for unsurveyed sites: A high reconnaissance is flow at approximately 300 ft above the site, offset to the site, and into the wind (if direction is known). Minimum speed is 50 kts. At the low reconnaissance the Pilot may descend to a minimum of approximately 50 feet above the highest obstacle along the flight path at a minimum speed of 50 kts. Without a high and low reconnaissance, at the Pilot discretion, the low reconnaissance may be performed on final approach if out of ground effect is available. There are occasions when the high and low reconnaissance need not be performed, such as when, among others, when performing known sites approaches. iFly’s AOC is limited to day VFR operations and their Safety Management System (SMS) Manual was approved by the HCAA. The Aircraft Commander was a 57 year old ex-military officer with almost 7,400 hours of flight experience. Almost half was fixed wing experience. Significantly only 62 hours involved flying single pilot helicopters (A109A & Cs) and all of that had been in the previous 8 weeks, since being employed by iFly. In response to the Aircraft Commander’s request for information on Galatas, he was sent Google Earth images (below) by the operator’s Flight Watch Department. AAIASB make no mention of a survey having been conducted at the site. The pilot e-mailed back that he knew the landing site. The Flight Watcher was aware that there were three medium voltage (20 kV) powerlines 314 m to theeast of the landing site crosses the channel between Galata and Poros Island. They were not visible on the images forwarded, but he was confident from the pilot’s response that the pilot knew the site and was aware of them. AAIASB also state that the charts the pilot had did not show them. The helicopter few the first sector to Galatas with just the pilot aboard. The helicopter approached in a left hand turn from the Southeast. It passed under the cables, landed and parked facing north. AAIASB don’t believe a site recce was conducted before the approach commenced. The two passengers, Russians who had disembarked from a yacht and were en route to Athens airport, boarded the helicopter about 40 minutes later. The helicopter came into a low hover and turned right to face East-Southeast for a take off with a slight tailwind. AAIASB consider this departure direction confirms the pilot was unaware of their near miss with the cables on approach although it may have been influenced by a desire to over fly the yacht several miles offshore to the north east. After take-off, the Helicopter moved horizontally for 8 s at low altitude, followed by a climb for 9 s and the next 3 s...
read moreDC3-TP67 CFIT: Result-Oriented Subculture & SMS Shelfware
DC3-TP67 CFIT: Result-Oriented Subculture & SMS Shelfware (North Star Air Basler DC3-TP67 C-FKAL) On 3 December 2019, North Star Air Douglas DC-3C Basler Turbo Conversions TP67 (DC3-TP67) C-FKAL impacted terrain 200 m short of the runway threshold at Sachigo Lake Airport (CZPB), Ontario while manoeuvring in poor weather during a daytime, supposedly VFR, cargo flight from Red Lake Airport (CYRL), Ontario. Both pilots escaped uninjured. History of the Accident Flight The Transportation Safety Board of Canada (TSB) explain in their safety investigation report, issued on 4 August 2022, that when the aircraft commander checked the weather at 0700 Local Time and instrument meteorological conditions (IMC) were reported. The aircraft commander had joined the company in 2017. He had 14,000 hours of experience (2,900 on the TP67 and c9,000 on the piston engine DC-3). He had been involved in another North Star Air TP67 accident on 20 June 2019. In contrast the co-pilot had only 1,100 hours of experience and North Star Air was his first job as a pilot. There was therefore a large cockpit gradient. The flight departed CYRL under visual flight rules (VFR) at 0800 The reported weather at the time was broken ceiling at 1200 feet AGL and an overcast layer based at 2000 feet AGL. Shortly after takeoff, the aircraft entered, and climbed above, the cloud layers before reaching the planned cruising altitude, which was not in accordance with the applicable regulations for VFR flights. At the Top of Decent the crew obtained the 0800 weather report for CZMD. This “remained generally unchanged” from the 0700 report. The crew… …elected to carry out a visual approach to Runway 10. The captain initiated a descent through the cloud layers by reference to the flight instruments. Once the aircraft broke out of cloud at very low level, the aircraft was not in a position to continue with the planned visual approach. Rather than a go-around: The captain made low-level manoeuvres in an attempt to land, flying a large 360° turn, as low as 100 feet AGL (i.e. about 400 feet below the required minimum altitude), and then flew a manoeuvre similar to a left-hand circuit, which brought the aircraft within close proximity to a significant obstacle (a 150-foot tall tower), in meteorological conditions below the VFR minimum requirements. Furthermore: Given that the captain had not briefed the first officer, the latter was unaware of the captain’s intentions and began calling out airspeed and altitudes. On the last attempt, during the low-level downwind leg, when the aircraft passed abeam the threshold of Runway 10, the captain initiated a left-hand turn and began descending. About 10 seconds later, the aircraft collided with terrain, in a near wings-level attitude, approximately 650 feet southwest of the threshold of Runway 10. The aircraft slid 350 feet southward along the ground before it came to a rest on a southwesterly heading. The ELT activated but as the antenna broke off the signal was not detected. The TSB Safety Investigation The investigators noted that… …during the 2 months before the occurrence, all the flights conducted by the captain had been in accordance with VFR. However, for more than 10% of the flights, the weather at destination was reported to be conducive to IMC. Additionally, approximately 35% of the flights were conducted in weather where the pilots would have lost visual reference to the ground at some...
read moreFuel Tube Installation Trouble
Fuel Tube Installation Trouble (Jet2 B757 G-LSAN) On 7 August 2012 Jet2 Boeing 757-2K2 G-LSAN diverted in flight after a fuel leak was detected. The UK Air Accidents Investigation Branch (AAIB) safety investigation report explains that approximately three hours into a post-maintenance check flight the flight crew identified a 600 kg lateral fuel imbalance. They determined this to be due to fuel leak from the right hand Rolls-Royce RB211-535E4 engine. The crew carried out the ‘Engine Fuel Leak’ QRH checklist, shutdown the right engine being shut down and diverted to Newcastle Airport. Inspection of revealed that the leak was from pump-end flanged joint of the fuel supply tube running between the high pressure (HP) fuel pump and the fuel flow governor. The fuel supply tube had been installed during the prior C-check as part of recommended Service Bulletin RB.211-73-G230. This SB was developed to the replace earlier standards of fuel tube that were the source of previous fuel leaks (e.g. as occurred to B757-28A G-TCBA on 12 June 2010). Investigators found one of the two bolts that attached the flange to the HP fuel pump body were only finger-tight and the O-ring seal had been nipped on installation, resulting in a portion being missing. The AAIB note that: Both attachment bolts were new items that had been fitted during the installation of the fuel tube, however the bi-hex head of the lower bolt exhibited an unexpected degree of galling consistent with a socket slipping off the head of the bolt during tightening of the bolted-flange joint. Examination showed the wire-thread insert had been ” ‘picked up’ during insertion of the bolt, causing a progressive roundingover of the bolt’s threads as the bolt was tightened”. However, trials done for the AAIB at an overhaul shop indicated that it was “unlikely that the damaged wire-thread insert caused the lower bolt to remain only partially inserted”. AAIB also checked the torque wrench used and confirmed it was properly calibrated. AAIB did observe fresh galling and scratch marks both around the lower bolt hole and the periphery of the fuel tube flange interface. This indicated that difficulty was experienced installing the fuel tube. Further investigation revealed that both engine pylons had needed to be removed during the C-check, so the SB had been incorporated with the engine removed from the aircraft and installed in a transport cradle. The lower parts of the engine, including the area where the fuel tubes were to be replaced, were close to the ground and partially obstructed by the cradle’s steel framework. These restrictions made access significantly more difficult than if the engine had been mounted on its pylon, or in an engine overhaul fixture. Additionally: Following the incident the engine manufacturer conducted an investigation into the installation difficulty of both the supply and overspill return fuel tubes as specified in the SB. This activity showed that for both fuel tubes, it was significantly easier for a mechanic to align and torque the HP fuel pump flange bolts before then tightening the fuel flow governor flange bolts, which is the reverse of the bolt tightening sequence specified in the SB. Retention of the O-rings within the grooves in the fuel tube flanges was also identified as a problem, particularly at the HP fuel pump ends where access and visibility are limited. Application of a viscous assembly fluid to specification OMat 1069, which is approved for use on fuel system components, was identified as...
read moreHeliski Flat Light Flight into Terrain
Heliski Flat Light Flight into Terrain (Alpine Air Alaska, AS350D, N99676) On 15 March 2022, Airbus AS350D N99676 of Alpine Air Alaska was damaged near Valdez. Alaska when landing on a glacier during a heliski operation. The pilot, the sole occupant, suffered minor injuries. The US National Transport Safety Board (NTSB) explain in their safety investigation report, issued on 5 July 2022, that the pilot had 9779 hours of flight experience and stated… …that while on approach….to pick up a group of skiers, flat light conditions made it difficult to discern topographical features on the snow-covered, featureless, glacial terrain. The pilot said that during the approach, he inadvertently allowed the helicopter to descend below his intended approach path… The helicopter touched down c 200m short of his intended landing site. The helicopter subsequently rolled to the left and the main rotor blades struck the snow-covered terrain. The helicopter sustained substantial damage to the main rotor blades, tail rotor blades, tail boom, and fuselage. NTSB Probable Cause The pilot’s failure to maintain a proper approach path in flat light conditions, which resulted in landing short of the intended landing spot and impact with terrain. Safety Resources The European Safety Promotion Network Rotorcraft (ESPN-R) has a helicopter safety discussion group on LinkedIn. You may also find these Aerossurance articles of interest: Canadian Flat Light CFIT – sadly this accident was fatal Antarctic Helicopter Accidents Alaskan AS350 CFIT With Unrestrained Cargo in Cabin Low Viz Helicopter CFIT Accident, Alaska Austrian Police EC135P2+ Impacted Glassy Lake Fish Spotting Helicopter Strikes Glassy Sea EC135P2 Spatial Disorientation Accident HEMS EC135T1 CFIT During Mountain Take Off in Poor Visibility A Short Flight to Disaster: A109 Mountain CFIT in Marginal Weather HEMS Black Hole Accident: “Organisational, Regulatory and Oversight Deficiencies” Taiwan NASC UH-60M Night Medevac Helicopter Take Off Accident RCMP AS350B3 Left Uncovered During Snowfall Fatally Loses Power on Take Off EC130B4 Destroyed After Ice Ingestion – Engine Intake Left Uncovered UPDATE 7 January 2023: Blinded by Light, Spanish Customs AS365 Crashed During Night-time Hot Pursuit UPDATE 30 August 2025: Flat Light B206L4 Alaskan CFIT & 11 Hour Emergency Response Delay UPDATE 15 February 2024: Transportation Safety Board of Canada (TSB) has published their safety investigation report into the crash of Airbus AS350B2 C-FYDA of Great Slave Helicopters on Griffith Island, Nunavut on 21 April 2021. Flat light was a factor. EHEST Leaflet HE 13 Weather Threat For VMC Flights: Aerossurance has extensive air safety, operations, SAR, airworthiness, 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...
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