TCM’s Fall from SAR AW139 Doorway While Commencing Night Hoist Training
TCM’s Fall from SAR AW139 Doorway While Commencing Night Hoist Training (Babcock MCS Spain EC-KLM) On 16 July 2018 Babcock Mission Critical Services Spain SAR Leonardo AW139 EC-KLM was conducting night rescue training offshore Valencia, Spain. Wind speed was low, 5 knots, and the sea was Sea State 2 (0.1 to 0.5 m waves). The aircraft was hovering, about 50 ft above a vessel when the rescuer exited the cabin to be hoisted down. They however fell from the aircraft into the sea. The rescuer was recovered by the aircraft and transferred to hospital. They suffered a serious injury, an upper crush fracture of the T12 vertebra. The Accident Flight On 30 June 2021 the Spanish Comisión de Investigación de Accidentes e Incidentes de Aviación Civil (CIAIAC) released their safety investigation report into this accident. This is only available in Spanish so we have translated it to compile for this summary. The helicopter, callsign Helimer 201, was based at Valencia as part of a contracted SAR service for the Spanish Maritime Rescue and Safety Society (SASEMAR). A routine flight was planned that night to maintain crew currency. The needs of each crew member were evaluated during the pre-flight briefing. They were prioritised based on which expiry date was closer and a suitable sequence agreed. After starting the engines at 23:00 Local Time, the aircraft headed offshore to rendezvous with a vessel for training. On board were two pilots and two Technical Crew Members (TCMs); a hoist operator and a rescuer (aka winchman). The hoist operator was 37 and dual qualified with 228 flying hours as a hoist operator and 746 as a rescuer. The rescuer was 34 and had 730 flying hours in that role. They are among 120 employed by the operator (70 of which are dual qualified). In the 15 days prior, the rescuer had been scheduled for two day shifts followed by two night shifts, five days off, five day shifts, followed by the night shift during which the fall occurred. On that morning they did however perform a routine mandatory medical examination (described as a ‘stress test’) at a hospital in Valencia. The TCMs were in the cabin of the AW139. The cabin can be separated from the cockpit by a roller blind and has independent lighting controls. The aircraft was equipped with an advanced digital intercom system (or ICS). The rescuer also carried POLYCOM and VHF radios. Inside the cabin there where four folding seats attached to the structure. Below is the seat used by the rescuer, showing the hardpoint where their harness lifeline is attached when they are moving in the cabin. This is one of four available to the TCMs. A dual hoist assembly is fitted to the right-hand side of the aircraft. There is the standard cabin step below the doorway (modified to avoid hoist cable snagging). As hand holds there are flexible handles on the sides of the doorway (shown above) and a rope that runs along the upper edge of the doorway. The training began with two approaches to hover alongside the vessel using the helicopter’s Automatic Flight Control Systems (AFCS). These were successfully completed before the next of two planned exercises; one to lower the rescuer to the vessel and then the recovery of a manakin from the water. During the second approach the rescuer prepared their...
read moreNVIS Autorotation Training Hard Landing: Changed Albedo
NVIS Autorotation Training Hard Landing: Changed Albedo (Tampa Police Bell 407 N512TP) On 21 June 2021 at 21:45 local time, Bell 407 N512TP of the Tampa Police Department (TPD) was damaged in a hard landing at the Tampa Executive Airport, Florida during autorotation landing training using a Night Vision Imaging System (NVIS). The pilot and instructor were uninjured. The Accident Flight The US National Transportation Safety Board (NTSB) safety investigation report, published on 19 October 2021, explains that the police pilot had 2721 hours of experience, 1472 on type and the contracted instructor had 2047 hours, 112 on type. Their experience operating with Night Vision Googles (NVGs) is not recorded by the NTSB however. A number of exercises had already been successfully conducted that evening in the Garmin 500H equipped helicopter. For this exercise: The pilot determined where on the runway he was going to land and entered the autorotation at an approximate airspeed of 60 knots. When the helicopter was about 90 to 100 ft above the ground, and the engine rpm was at 99-100%, he entered the flare. At the bottom of the flare, the pilot “bumped” up the collective to arrest the rate of descent and levelled out at what he thought was about 7-10 ft above the runway. At that point, the pilot said it felt like the bottom of the helicopter started to fall out from underneath him. Pulling collective had no effect on arresting the sink rate. The low rotor rpm horn sounded right before the helicopter landed hard on the runway. The impact was sufficient to flex the main rotor blades and sever the tail boom. The Safety Investigation The training provider reported that the police pilot had “conducted hundreds of NVG power-off landings to this exact location”. However, since the last one the runway had been repaved. Meanwhile the instructor had not done training at that site but knew it had been used successfully by colleagues for many years when training the TPD. The training provider noted that: The newly paved runway is a deep, dark black color. Due to this fact, its Albedo is near zero. The previous runway color was light gray with mid to high Albedo. They explain: Albedo is a non-dimensional, unitless quantity that indicates how well a surface reflects solar energy. Albedo commonly refers to the “whiteness” of a surface, with zero meaning black and 1 meaning white. A value of zero means the surface is a “perfect absorber” that absorbs all incoming energy. They comment that the new surface would therefore be “like a black hole”. EASA explain in GM1 SPA.NVIS.140: Contrast is one of the more important influences on the ability to correctly interpret the NVG image, particularly in areas where there are few cultural features. Any terrain that contains varying albedos (e.g., forests, cultivated fields, etc.) will likely increase the level of contrast in a NVG image, thus enhancing detail. The more detail in the image, the more visual information aircrews have for manoeuvring and navigating. Low contrast terrain (e.g., flat featureless desert, snow-covered fields, water, etc.) contains few albedo variations, thus the NVG image will contain fewer levels of contrast and less detail. The training provider concluded: Although the profile was correctly flown by the flight crew, the crew encountered a near zero Albedo of the runway surface in the final, most critical aspect of the maneuver which is during the power-off landing phase. This caused an optical illusion of false height and speed relative...
read moreBell 407 Rolls-Royce 250-C47B Uncontained Engine Failure after Bearing Failure
Bell 407 Rolls-Royce 250-C47B Uncontained Engine Failure after Bearing Failure (N120HH) On 24 June 2020 privately owned Bell 407 N120HH was destroyed after an uncontained Rolls-Royce 250-C47B engine failure near Long Marston in Warwickshire, UK. The Accident Flight The UK Air Accidents Investigation Branch (UK AAIB) explain in their safety investigation report (published 30 September 2021) that: The pilot collected the helicopter the day before the accident from Thruxton Aerodrome, Hampshire, where it had been undergoing an annual maintenance check. The maintenance work package included…the 300-hour maintenance inspection on the engine. Unscheduled work arising from this maintenance included replacement of the main transmission freewheel unit and pitch horns. The latter resulted in a requirement for a torque check on the main rotor mast assembly after the helicopter had flown 3 to 4 hours. Almost one hour was flown that day and several flights were intended on the day of the accident, intended to culminate in a return to Thruxton for the torque check. Before the first [55 minute] flight the pilot completed a walk-around, which included opening the engine cowlings and checking the fluid levels; he did not find any abnormalities. The engine oil level was showing as FULL on the sight glass. The pilot reported that the oil tank sight glass was clear and simple to read. By slightly nudging the helicopter he could clearly see the oil level moving. The oil level was still at FULL prior to the second flight, a private sightseeing flight from Wellsbourne Mountford Aerodrome, Warwickshire over the Malvern Hills. On board was the pilot and one passenger. Two witnesses noticed the helicopter as it was flying towards Wellsbourne (Witness 1 and 2). The first witness was just south of Bidford-on-Avon. He saw the helicopter flying towards him from the west and could see the helicopter clearly through his binoculars. He described seeing what looked like a “contrail” coming from above the cabin but below the rotor. He watched the helicopter as it passed overhead and flew to the east; the ‘contrail’ continued throughout this time. In the distance he saw it turn to the south but did not see the accident. The occupants were not aware of the ‘trail’ behind the helicopter The second witness, who was near Dorsington described seeing “white smoke” coming from the helicopter and took a couple of photographs. As it passed him, he heard a “popping noise”, saw the smoke turn grey and saw the helicopter descend to the ground near Long Marston. The helicopter was flying at approximately 1,800 ft amsl (approximately 1,700 ft agl) and 118 kt with the engine torque at 70 to 75%. The first indication in the cockpit of a problem was an amber [Full Authority Digital Engine Control] FADEC FAULT light on the Caution and Warning Panel (CWP). When the pilot checked the instruments, he saw the NR [Main Rotor Speed] was at 100% and the NP [Power Turbine Speed] was at 90%. In normal powered flight NP is equal to NR. He recalled looking at the torque and seeing a “5” but could not remember if it was fifty something percent or 5%, he did not recall the NG [Engine Gas Generator Speed]. The other engine instruments appeared normal. The pilot… …reduced the throttle slightly to match the throttle position to the NG then selected the FADEC mode to manual . He...
read moreItalian Alps AW139 Mountain Rescue Hoisting Blade Strike
Italian Alps AW139 Mountain Rescue Hoisting Blade Strike (Vigili del Fuoco I-TNDD) On 7 October 2017 Leonardo AW139 I-TNDD of the Vigili del Fuoco fire and rescue service was conducting a hoist rescue mission at Monte Casale, near Trentino in Northern Italy, when it suffered a main rotor blade strike on a cliff face. The aircraft landed safely and an attempt was made to assess the damage while rotors running. The aircraft then made a further flight to Trento Mattarello Airport. The Accident Flight The Italian National Agency for Flight Safety (ANSV) explain in their safety investigation report (issued only 0n Italian on 8 September 2021) that the aircraft had been tasked at 08:14 after the fall of a young climber. The boy was near the base of a cliff at 2100 ft AMSL. The weather was good and the wind was negligible. On board the hoist-equipped helicopter were three crew (pilot, hoist operator and winchman) and two medical personnel. The single pilot had 5992 hours of experience, 715 on type and 3200 hours of HEMS / rescue flying. If a HEMS mission the hoist operator would have been sat next to the pilot as the HEMS Technical Crew Member (TCM) on the outbound flight. The unit at Trentino had two AW139s and an Airbus AS365N3. In 2016 it had carried out 2488 taskings and flew 1059 hours. The casualty was rapidly located and initially the winchman was lowered to assess the casualty. Then while hoisting down the two medical personnel from c 25-20 m AGL at 08:27 there was “a slight variation in the noise of the rotor itself is heard and consequently a slight oscillation of rotor revolutions and torque occurs”. The ANSV comment that only the pilot appeared to notice this. A few seconds later the pilot told the hoist operator that a blade strike had occurred and they had seen “a cloud of dust on the [cliff] wall, in the upper left”. The aircraft diverted to Pietramurata, about two minutes away. During that flight no abnormal vibration was felt. After landing, the rotor remained running as the hoist operator exited the aircraft to examine the rotor tips. Damage was evident but after discussion the decision was made to return to home base at Trento Mattarello Airport, influence by the lack of vibration. During that 6 minute 20 second flight, there was further discussion on the incident. The pilot believed they must have struck a well camouflaged outcrop having been convinced they had c 1.5 m of clearance. On shut down it was found that the helicopter suffered loss of 70 – 80 mm of each of the five main rotor blades and damage to the leading edge protection strips. Safety Investigation / Analysis The ANSV comment on the pilot workload when operating single pilot and note that… ….listening to the CVR shows the complexity of the rescue intervention… They comment that: It is reasonable to believe that the greyish-yellow background of the rock face…the helicopter was positioned orthogonally [from] did not help the pilot in determining the distance of the main rotor blades from the wall itself, taking into account that the blades, in the last part, are painted yellow to define the outer limit, however, blending in with the background of the aforementioned wall. The ANSV note that the helicopter was not equipped (nor was it required to be equipped)...
read moreRLC B407 Reverses into Sister Ship at GOM Heliport
RLC B407 Reverses into Sister Ship at GOM Heliport (Bell 407s N662RL and N668RL at Paterson, LA) On 25 September 2021 Rotorcraft Leasing Company (RLC) Bell 407 N662RL was lifting off for departure from a heliport in Patterson, Louisiana when it drifted backwards into Bell 407 N668RL. Documents filed with the US National Transportation Safety Board (NTSB) state that N662RL was departing from pad D3 at the RLC Patterson heliport with one pilot and three passengers aboard. They were destined for a Gulf of Mexico offshore installation in Mississippi Canyon Block 194 (MC194) and then Ewing Bank Block 873 (EW873). The pilot had 1479 hours of flight experience, 255 on type. The tail rotor of N662RL contact the main rotor of N668RL that was rotor running with passengers aboard on pad D5. N662RL landed hard in a ditch. The three occupants of N662RL were uninjured and there are no reports of other injuries. Minimal information is in the NTSB Preliminary Report at time of writing. The RLC Patterson heliport is to the south of Harry P. Williams Memorial Airport, Patterson, an airport that features a runway and a seaway for floatplanes. The heliport has a typical non-ICAO Annex 14 compliant GOM heliport configuration and this accident highlights the challenges that some of the more fanciful Advanced Air Mobility vertiports will face. UPDATE 16 November 2021: The NTSB issued the following unhelpful statement as their probable cause: The pilot’s failure to maintain adequate clearance from a parked helicopter while hovering to reposition for takeoff. We consider this unhelpful as it is simply a self-evident statement of the circumstances, not an explanation of why the accident happened. 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: South Korean Fire-Fighting Helicopter Tail Rotor Strike on Fuel Bowser Ditching after Blade Strike During HESLO from a Ship US BSEE Helideck A-NPR / Bell 430 Tail Strike GOM Helicopter Ops 2000-2019: Single Engine Usage Plummets But Fatal Accident Rate Resistant Air Ambulance B407 Hospital Helipad Deck Edge Tail Strike During Shallow Approach Cessna 208B Collides with C172 after Distraction S-76C+ MLG Collapsed Due to Pothole Troublesome Tiedowns Troublesome Tiedowns: The Sequel UK AAIB Report on Two Ground Collisions Ground Collision Under Pressure: Challenger vs ATV: 1-0 Gazelle Caught Out Jumping a Fence S-92A Collision with Obstacle while Taxying Helicopter Destroyed in Hover Taxi Accident Pilatus PC-12 Collided with Pick-Up Truck During Dusk Take Off Air Ambulance Helicopter Downed by Fencing FOD Ambulance / Air Ambulance Collision Inappropriate Autorotation Training: Police AS350 Stabilised Hover Prevents Loss of Control Accidents Say FAA Hazardous Hangar Hovertaxy A Lethal Cocktail: Low Time, Hypoxia, Amphetamine and IMC Don’t Be a Sucker!: Cabri Canopy Implosion Mind the Handrail! – Walk-to-Work Helideck Hazard Impromptu Landing – Unseen Cable Alpine MAC ANSV Report: Ascending AS350B3 and Descending Jodel D.140E Collided Over Glacier Mid-Air Collision of Guimbal Cabri G2 9M-HCA & 9M-HCB: Malaysian AAIB Preliminary Report AAIB Highlight Electronic Conspicuity and the Limitations of See and Avoid after Mid Air Collision North Sea S-92A Helicopter Airprox Feb 2017 USMC CH-53E Readiness Crisis and Mid Air Collision Catastrophe Avoiding Mid Air Collisions: 5 Seconds to Impact Fatal Biplane/Helicopter Mid Air Collision in Spain, 30 December 2017 A319 / Cougar Airprox at MRS: ATC Busy, Failed Transponder and Helicopter Filtered From Radar Merlin Night Airprox:...
read moreDon’t Be a Sucker!: Cabri Canopy Implosion
Don’t Be a Sucker!: Cabri Canopy Implosion (Swiss Helicopter Guimbal G2 HB-ZDQ) On 1 July 2020 Swiss Helicopter Guimbal Cabri G2 HB-ZDQ was conducting a training flight near Vaulruz in Switzerland when the helicopter’s canopy shattered. The Swiss Transportation Safety Investigation Board (STSB) explain in the safety investigation report (in French) that both student and instructor suffered minor injuries to their face, hands and legs. The Flight The serious incident occurred during an exercise to demonstrate handling at close to Vne (Velocity, Never Exceed) at c119 kt at a pressure altitude of 5500 ft. While passing the indicated speed of 110 kt, the plexiglass canopy suddenly burst. Due to the high relative wind, a lot of debris ended up in the cockpit, the headsets and glasses of the two crew members were torn off. The instructor decreases the speed, puts on his second pair of prescription glasses which is in his trouser pocket and decided to land as quickly as possible. The implosion was significant enough to trigger the Emergency Locator Transmitter (ELT). The helicopter landed safely on a football field about 5 minutes later. The Safety Investigation The one-piece plexiglass Capri canopy is 2 mm thick and glued to the fuselage around its perimeter. The investigators note that the “canopy has been designed to withstand aerodynamic stresses” and that these are highest at high speed. At the site of the serious incident, it was observed that a suction cup attachment was installed on the canopy. Such an installation makes it possible to fix an on-board camera, for example, but it was not provided for by the manufacturer and can generate additional stresses on the one-piece canopy and consequently weaken it. Safety Action Guimbal issued Service Letter, SL 20-001 A which advises owners not to attach items to the canopy with a suction cup mount. The investigators note that Airbus Helicopters has also recently issued safety promotion notice 3587-P-00, encouraging the wearing of a helmet. 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: AS350B3/H125 Bird Strike with Red Kite Safety Lessons from a Fatal Helicopter Bird Strike USAF HH-60G Downed by Geese in Norfolk, 7 January 2014 Deadly Dusk Air Ambulance Bird Strike Swedish Military NOE Helicopter Bird Strike Power of Prediction: Foresight and Flocking Birds looks at how a double engine loss due to striking Canada Geese had been predicted 8 years before the US Airways Flight 1549 ditching in the Hudson (which was just days after a Louisiana helicopter accident). Hanging on the Telephone… HEMS Wirestrike A Short Flight to Disaster: A109 Mountain CFIT in Marginal Weather Gazelle Caught Out Jumping a Fence Fatal B206L3 Cell Phone Discount Distracted CFIT Austrian Police EC135P2+ Impacted Glassy Lake A Lethal Cocktail: Low Time, Hypoxia, Amphetamine and IMC Mid-Air Collision of Guimbal Cabri G2 9M-HCA & 9M-HCB: Malaysian AAIB Preliminary Report AAIB Highlight Electronic Conspicuity and the Limitations of See and Avoid after Mid Air Collision RLC B407 Reverses into Sister Ship at GOM Heliport 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...
read moreA Lethal Cocktail: Low Time, Hypoxia, Amphetamine and IMC
A Lethal Cocktail: Low Time, Hypoxia, Amphetamine and IMC (R44 N744TW Utah) On 17 May 2019, private Robinson R44 N744TW was destroyed in an accident near Alpine, Utah. The pilot and passenger both received fatal injuries. The Accident The US National Transportation Safety Board (NTSB) safety investigation report, published on 15 October 2021, explains that the 32-year-old pilot had just 145 hours total flight time, 32 on type. He had “started an oil fracking company” and had rented the R44 from Utah Helicopters, where he had been trained (mostly on R22s). He had departed Myton, Utah, at 09:30 with his wife, intending to fly to South Valley Regional Airport (U42), West Jordan, Utah, to pick up a second passenger before proceeding to Phoenix, Arizona. A witness stated “it was raining lightly at that time.” There was no record of the pilot receiving any preflight weather information from an access-controlled source. During the flight the pilots mother received several texts from the pilots wife and at 10:27 a video… …showing the helicopter above a thick cloud layer with no discernible horizon. Some of the cloud tops appeared above the helicopter. The NTSB explain that: Radar data provided by the Federal Aviation Administration (FAA) revealed a target correlated to the accident helicopter first appear on radar at 0956 at an altitude of 10,400 ft mean sea level (msl), on a heading of 309° about 44 miles west of [Myton]. The helicopter continued generally on a west-northwest course… The airspeed initially varied from 37 to 88 knots ground speed but stabilized to about 85 knots for most of the flight. The helicopter climbed to 13,000 ft msl at 1007 and remained between 12,700 and 13,000 ft ft msl until about 1030, when it descended below 12,500 ft msl. The helicopter was not equipped with a supplemental oxygen system, nor were any supplemental oxygen provisions found at the accident site. At 1031, the helicopter began a right descending right turn that continued until radar contact was lost at 1033 at an altitude of 9,200 ft msl and groundspeed of 108 knots, about 1,650 ft from the accident site. The data revealed that the helicopter completed about 2.5 360° turns before radar contact was lost. NTSB Investigation & Analysis The wreckage was highly fragmented, consistent with a high-speed impact. Examination of the airframe and engine revealed no evidence of any preaccident mechanical failures or malfunctions. Weather radar imagery above the accident location between about 8,600 ft and 14,200 ft msl identified reflectivity consistent with light rain in an area that included the accident site. The helicopter was likely operating in visual meteorological conditions above the clouds until its initial descent from about 13,000 ft, at which point the helicopter likely entered and remained in instrument meteorological conditions for the rest of the flight. Although the altitude and duration of the flight did not meet regulatory requirements for supplemental oxygen use, it is likely that the pilot may have been experiencing some early effects of hypoxia, including euphoria, which may have exacerbated the effects from his use of multiple drugs. Toxicology testing revealed a blood level of amphetamine (around 300 ng/ml) and the presence of phenylpropanolamine, indicating that the pilot was most likely using a street preparation of the drug. Generally, levels above 200 ng/ml are the result of mis-using amphetamine to maximize its psychoactive effects. Testing also identified phenylpropanolamine and oxycodone in blood and urine, and oxazepam in urine. The…pilot had reported no medical conditions and no use...
read moreSouth Korean Fire-Fighting Helicopter Tail Rotor Strike on Fuel Bowser
South Korean Fire-Fighting Helicopter Tail Rotor Strike on Fuel Bowser (Heli Korea Sikorsky S-76C+ HL9661) On 25 April 2020, fire-fighting Sikorsky S-76C+ HL9661 of Heli Korea suffered a tail rotor strike on a fuel bowser landed at a forward operating base at the edge of the Yeongsan River, South Korea. There were no casualties of loss of containment of fuel but the helicopter received substantial damage. The Korean Aviation and Railway Accident Investigation Board (ARAIB) safety investigation report was published on 29 June 2021 (in Korean only). The Accident Flight The flight crew of two had been on duty since 08:30 at the forward operating base. One licenced aircraft engineer and a fuel bowser driver were also on site. The pilots had gone for lunch at 11:35, but they were called out at 11:52 to tackle a mountain forest fire. The helicopter took off at 12:12 and was on scene at 12:25. After an hour of fire-fighting with an underslung fire-fighting bucket the crew decided to return for fuel. At the operating base, the wind was 35 knots gusting 45. Due to the wind direction the approach was in the opposite direct to normal. The helicopter flew over the fuel bowser and placed the fire-fighting bucket on the ground next to the engineer and bowser driver. The accident investigators then suggest the wind caused the helicopter to drift backwards, although it seems reasonable to expect that after placing the bucket on the ground the helicopter would manoeuvre aft to land with the bucket and sling ahead of the nose. What is known is that the aircraft commander “felt the aircraft’s nose turning to the right with a thump and quickly lowered the collective”. The tail rotor had in fact contacted the upper deck of the bowser. The helicopter rotated 450° before coming to rest. Fragments of broken tail rotors were widely scattered around the site. The ARAIB Safety Investigation There is no mention of any flight data recorder data being available. The investigators note that in Heli Korea’s procedures: There was no information about the parking location of the feeling vehicle [and] here was no information about the [aircraft] parking position when a refuelling vehicle, which is fundamentally important for operational safety, was waiting for refuelling. The investigator state the co-pilot should advise the aircraft commander of obstacles, and mention the importance of Crew Resource Management (CRM) but then say rather harshly in this case “it is judged that there was no active action or advice” by the co-pilot. They also complain of the weeds growing on landing site. However, matters not discussed in the accident report: The approach briefing The decision to pass over the bowser rather than an offset approach and crab sideways Communications with the ground crew before or during the approach The positioning of the ground crew (which may have influence where the bucket was laid down) A recent prior accident involving the operator: On 18 March 202o Heli Korea Bell 214B1 HL9171 crashed into trees in strong winds during firefighting. with one fatality Another accident that occurred prior to the report being published: On 21 April 2021 Heli Korea S-76C+ HL9285 crashed into a lake during firefighting. with one fatality ARAIB Conclusions The cause of the accident was landing in strong winds, and unable to maintain position the helicopter was pushed backwards, and the tail rotor impacted the top of...
read moreEmergency S-76D Landing Due to Fumes
Emergency Sikorsky S-76D Landing Due to Fumes (Air Ambulance N761AF of Arkansas Children’s Hospital) The US National Transportation Safety Board (NTSB) has recently (5 Oct 2021) opened the public docket on an accident that occurred to Sikorsky S-76D air ambulance N761AF of Arkansas Children’s Hospital on 15 May 2019. The helicopter received substantial damage after an event that occurred in the cruise flight near Morrilton, Arkansas. None of the 6 occupants were injured. NTSB have since issued their probable cause so we have updated the article below. The Accident Flight The NTSB safety investigation report explains that 43 minutes into the flight the pilot experienced fumes in the cockpit. He turned off the environmental control system and commenced a descent. He recounted that: Within approximately 10 seconds, system visual and aural warnings indicated smoke within the aft baggage compartment so I initiated an emergency descent and landing to the [Morrilton Municipal] KBDQ airport declaring an emergency…[and]…requesting crash/fire/rescue from the town managing KBDQ be dispatch to the uncontrolled airport. I alerted the Arkansas Children’s Hospital communications center of the situation and made a landing and shutdown at KBDQ without further complication. The Safety Investigation The NTSB explain that… …examination of the helicopter by a FAA inspector revealed that the exhaust duct from the No. 2 engine was disconnected and not in its seated position. Exhaust from the No. 2 engine entered the compartment containing the tail rotor drive shaft and resulted in heat damage to drive shaft and surrounding areas. The exhaust ducts are attached using two bolts secured at 110 ft-lbs of pressure. Upon inspection of the No. 1 engine, as well as the operator’s second helicopter, all bolts were found partially disengaged and not tightened to the specified torque value. Lock wire is not required to be applied to these fasteners. The NTSB concluded that: The maintenance history of these components was not determined, but given the available information, it is likely that they were improperly secured, which resulted in their loosening and subsequently allowed the exhaust duct to become unseated. NTSB Probable Cause The improper securing of the exhaust duct bolts, which resulted in the duct becoming unseated and substantial heat damage to the tail rotor drive shaft. While this doesn’t explain why, the NTSB have classified this accident: Aircraft Fasteners – Incorrect service/maintenance Aircraft (general) – Incorrect service/maintenance Personnel issues (general) – Maintenance personnel Another Exhaust Duct Accident – A More Dramatic Outcome (Agusta A109A G-DNHI, 9 October 2006) The UK Air Accidents Investigation Branch (AAIB) report that Agusta A109A G-DNHI was also in the cruise when… …an engine exhaust duct separated from the helicopter and struck the tail rotor assembly, causing the tail rotor gearbox to also separate. After an initial yaw to the right, the pilot regained limited control. However, a further sudden yaw, possibly associated with a partial structural failure of the upper vertical stabiliser, prompted an immediate autorotative descent, which culminated in a successful forced landing. The investigation established that a [Mormon / U-band] clamp attaching an exhaust duct to the left engine had failed, due to stress corrosion cracking, allowing the duct to disconnect from the engine. Two AAIB safety recommendations were raised. 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: Ungreased Japanese AS332L Tail Rotor...
read moreGazelle Caught Out Jumping a Fence
Gazelle Caught Out Jumping a Fence (N505HA) On 5 September 2018, a privately owned Airbus Helicopters (formerly Aérospatiale) SA341G Gazelle N505HA crashed while hovering at Kortrijk-Wevelgem International Airport (KJK/EBKT) near Wevelgem, Belgium. The Accident The Belgian Air Accident Investigation Unit (AAIU) explain in their safety investigation report, issued on 22 June 2021, that: On the day of the accident, the pilot wanted to bring 3 friends for a lunch in Valenciennes (France). The helicopter was parked between two hangars located landside approximately 86 m north of the airfield perimeter, which is delineated by a 1.8 m high fence. The Gazelle main rotor diameter is 10.5 m (D value is 12). After the pre-flight inspection and the boarding of the passengers, the helicopter took off vertically to an altitude of 25 ft AGL, a little higher than the roof of the hangars. At the end of the vertical climb, when the pilot slightly pushed on the cyclic to gently move forwards, he felt twice a yaw movement of the helicopter and, after a quick check on the instrument panel, he noticed that the red ALARM warning light was on. He immediately lowered the collective pitch control and pushed the cyclic control further forwards to gain some forward velocity, before flaring and trying to land the helicopter on the grass area bordering the airport fence. A witness…heard the characteristic sound of an engine surge (a loud bang) before the helicopter moved down. The helicopter landed very hard on the grass strip between the circulation road and the airport fence, breaking the skids upon impact and causing significant belly damage. One blade of the main rotor hit one of the fence poles and sent it 50 m away, on the runway. The helicopter finally came to rest on its left side with the engine still running. The pilot shut down the engine, closing the fuel shut off valve. Despite a significant loss of fuel through the vent lines of the fuel tank, there was no post-crash fire. Three occupants were uninjured and one had only minor injuries. The Belgian AAIU Safety Investigation: The Engine Surge The helicopter was technically in good working condition, airworthy with no technical condition having directly caused the crash. The pilot-owner stated that he had washed the helicopter exterior the day before the crash. However, the engine’s air intake was found to be particularly dirty. To start up the engine, the pilot moved the FFC lever forward, but the lever was not latched in the notch during take-off. The slight friction between the FFC lever and the panel, and the extinguishing of the red ‘ALARM’ warning light, may have influenced the pilot from moving fully forward and latching the lever. The pilot was probably not aware of the crucial importance of latching the lever… The improper setting of the fuel flow control (FFC) lever and the dirty airpath of the engine air intake would have eroded the surge margin of the engine. When transitioning from the hover to forward flight…the engine compressor surged. The light tailwind and the rotor downwash hitting the surrounding buildings and so disturbing the airflow may have been a contributing factor. The AAIU note that: Moving the helicopter from the hover in ground effect (HIGE) to forward flight demands the most power during take-off. To avoid a compressor surge, the Flight Manual therefore instructs to slightly increase...
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