Fatal 2019 DC-3 Turbo Prop Accident, Positioning for FAA Flight Test: Power Loss Plus Failure to Feather
Fatal 2019 DC-3 Turbo Prop Accident, Positioning for FAA Flight Test: Power Loss Plus Failure to Feather (N467KS) On 21 January 2019 a 1944 Douglas DC-3C-65TP, N467KS, owned by Priority Air Cargo and operated by AFM Hardware, was involved in a take-off accident in Kidron, Ohio. Both pilots onboard were fatally injured. The Accident Flight The US National Transportation Safety Board (NTSB) explain in their safety investigation report (issued in November 2020) that the aircraft… …was the prototype for an Amended Supplemental Type Certificate (STC) project to add newer model Pratt and Whitney Canada (P&WC) PT6A[-67F] series engines and MT propellers to the existing STC. Flight Manual extracts in the public docket suggest this was the ‘Preferred Turbine -3‘ STC. The airplane was issued an experimental airworthiness certificate on July 27, 2018. Following several project meetings with the Federal Aviation Administration (FAA), certification and flight test plans were created. On the day of the accident: The airplane was loaded with ballast to maximum gross weight and was being positioned from Stoltzfus Airfield (OH22), Kidron, Ohio, to Akron Canton Regional Airport (CAK), North Canton, Ohio, to pick up a FAA test pilot for initial flight testing of stall maneuvers. The aircraft commander, who appears to have been the Pilot Flying, was 55 and had 15457 flying hours experience, 5612 on type. He was DC-3TP Part 125 check airman and was the chief pilot for AFM Hardware. This was his eighth flight in the aircraft since the PT6As were fitted. The co-pilot was 56 and had 9969 flying hours experience, 12 on type and this was his fourth flight in this aircraft with PT6As installed. The cockpit voice recorder (CVR) began recording before takeoff, about 0902. Crucially: According to the recording, the captain elected to forego the auto-feather system and overspeed governor tests that were listed in the “run up” section of the normal checklist because of the snow packed conditions on the taxiway and runway. As the captain was completing the before takeoff checklist, he stated all four boost pumps were on and all annunciator panel lights were extinguished. The captain briefed the takeoff decision speed (V1), rotation speed (Vr) and climb speed (V2) of 82, 84, and 90 knots respectively. Soon after liftoff [at 0911:27] and about 3 seconds after decision speed (V1), the left engine lost total power. The propeller began to auto-feather but stopped feathering about 3 seconds after the power loss. Witnesses observed white smoke exiting the left engine exhaust system immediately after takeoff and the airplane banked and yawed left. At 0911:35 and 0911:39, the captain made brief comments that indicated he was struggling to fly the airplane. The airplane yawed and banked to the left, descended, and… struck power lines and trees before impacting terrain [at 0911:40]. The airplane came to rest about 600 ft from the end of runway 19 and about 700 ft to the left of the runway centerline. The main wreckage was upright and oriented on a northwesterly heading, with the fuselage separated forward of the wings. NTSB Safety Investigation Downloaded automated data acquisition system (ADAS) data indicated left engine torque, fuel flow, gas generator speed (Ng), propeller rpm (Np) rapidly decreased at 0911:26.5. At 0911:27.2, left engine torque dropped to nearly zero and Ng decreased until the end of the recorded data. Left engine Np dropped to 746 rpm at 0911:30, then increased to 1050 rpm about 4 seconds later. Airspeed reached a maximum of 91 knots at 09:11:31. Recorded engine data indicated the power loss was...
read moreWindscreen Rain Refraction: Mountain Mine Site HESLO CFIT
Windscreen Rain Refraction: Mountain Mine Site HESLO CFIT (Aberdeen Helicopters Airbus AS350B2 C-FAHC) On 17 August 2020 Airbus Helicopters AS350B2 C-FAHC of Aberdeen Helicopters impacted a mountainside near Eskay Creek Mine, Iskut River, 45 nm from Stewart, British Columbia. This was during Helicopter External Sling Load Operations (HESLO) supporting mineral exploration. The pilot, the sole occupant, died in this Controlled Flight Into Terrain (CFIT) accident. There was also a post crash fire. The Accident Flight The Transportation Safety Board of Canada (TSB) explain in their safety investigation report (issued 9 March 2021) that the pilot started work at 0652. This was his second summer flying in that area in support of the exploration company. He had 2800 flying hours of experience, 900 on type. His first task was to fly the day shift crew to their drill sites on Nickel Mountain, BC and returning the night shift crew to Garibaldi Camp (located 9 nm from the drilling site). The pilot picked up another two workers from the camp, dropped them off on the mountain, and, at approximately 0750, landed at Pad 27 the Volcano staging area, approximately 1 nm from the drilling site. The pilot returned to Pad 27 at approximately 0854 to resume the longline operation to move the drill rig. During one of the 11 lifts, the pilot communicated that he would have to hover in place due to reduced visibility before he could continue with the lift. The visibility improved and the rig transfer continued. At approximately 1006, the pilot returned to the Volcano staging area to refuel. At 1022, the pilot returned to Pad 27 to move the last piece of the drill rig. After the drill foreman had hooked the load up to the helicopter’s longline, the pilot communicated that poor weather was approaching and that he was unable to take the load. The load was disconnected and the helicopter hovered in place for approximately 1 minute. At 1024, the pilot backed away from the drill pad downslope (southwestward) at a ground speed of between 1 and 2 knots and stopped approximately 200 feet away. He then moved back toward the pad, and the drill crew asked if they should remove the longline. The pilot said it was not necessary, and at 1025:40, he turned and began to accelerate on a southwestward track. Heavy rain began at this time. Over the next 30 seconds, global positioning system (GPS) data showed that the helicopter continued southwest and accelerated to a ground speed of approximately 70 knots at GPS altitudes of between 5600 feet above sea level (ASL) and 5500 feet ASL. At 1026:02, the pilot released the longline from the helicopter onto the hillside about 800 feet west of Pad 27 and, 9 seconds later, the helicopter began to track to the right in a turn at approximately 5° per second. The change in altitude during this turn was less than 100 feet. The turn continued until just after 1026:27, when the helicopter collided with terrain… at approximately 5500 feet ASL on a steep mountainside. The damage was consistent with a high-energy impact. Most of the aircraft was consumed by the post-impact fire with the exception of the tail boom and the floorboard area of the cabin. Emergency Response When the heavy rain began, the drill crew at Pad 27 sought shelter in the survival shack at the drill site. They emerged after approximately 15 minutes and, assuming the helicopter was waiting at the Volcano staging area, attempted to contact the pilot by radio. The crew at...
read moreAS350B3 Ditching Japan
Airbus Helicopters AS350B3 Ditching Japan (Excel Air Services JA350D) On 8 June 2018, Airbus Helicopters AS350B3 JA350D of Excel Air Service, ditched c 41 km NW of Naha airport while en route to Aguni airport. The pilot was seriously injured. The Accident Flight The Japan Transport Safety Board (JTSB) explain in their safety investigation report that while in cruise at c 110 kt and 1,000 ft at around 15:25 the pilot heard a warning ‘gong’, the engine governor light (GOV) illuminated and the pilot had to counter a right yaw. Main rotor speed (NR) also reduced. The pilot disengaged the autopilot (AP) and slightly lowered the collective pitch (CP) lever in an attempt to maintain NR. After confirming that NR indicator showed around 370 rpm in warning control range (yellow arc line: between 320 and 375 rpm), the pilot operated emergency control in case of governor failure. The pilot shifted the twist grip to manual operation and turned it to the left; however, the pilot was unable to position NR in normal control range (green arc line: between 375 and 394 rpm), and the altitude of the helicopter kept going down. NR stabilised at around 370 rpm. The pilot felt the flying controls had become heavy,”as in the case that hydraulic system was off”. The pilot [3,474 flight hours total time, 1,887 hours on type] had not experienced [practical] training of emergency control for the case of governor warning light failure, and had [only] verbally confirmed the procedures simulating the failure in regular training. The pilot turned the twist grip only to the left paying attention to avoid an excessive NR, but was unable to increase NR. Because the helicopter did not stop descending and came as close as about 300 ft to the sea surface, the pilot made a decision to ditch at this time. The Flight Manual Supplement for the Emergency Flotation System (EFS) states: Ditching at 10 kt or less is recommended. Ditching must be as horizontal as possible. Ditching with power on requires deceleration to 5 kt or less before lowering the collective lever after ditching. JTSB explain that: At 15:25:30, the pilot sent [a] distress message and manually activated emergency locator transmitter (ELT). The pilot thereafter strongly pulled the cyclic stick to decelerate for ditching and [deployed] the emergency floats at about 50 kt. The helicopter came near to the sea surface in 10 to 20 seconds after sending the distress message, and ditched at the speed of 20 to 30 kt without performing a sufficient deceleration. The helicopter immediately sank to the level of the pilot’s seat. The pilot unfastened shoulder harness and seat belt while dipped in the sea, escaped from the helicopter without putting on a life jacket [which was stored under his seat]. The pilot initially held on to an EFS float bag to await rescue. Fortuitous a SAR helicopter of the Japan Air Self-Defense Force was exercising near-by and it… …received the distress message, arrived near the accident site around 15:39 and found the pilot on the sea. The helicopter had already sank in the sea at this time. The pilot was rescued by the rescue helicopter and was taken to the hospital in the city of Naha via Naha airport around 16:20. When the rescue helicopter arrived at the accident site, it received a weak ELT signal near the site where the helicopter had sank, which...
read moreSAR AW139 Dropped Object: Attachment of New Hook Weight
SAR AW139 Dropped Object: Attachment of New Hook Weight (Sapporo City Fire Department JA17AR) On 16 February 2020 objects were dropped from Leonardo AW139 SAR helicopter JA17AR of the Sapporo City Fire Department Air Corps during rescue hoist training at Ishikari City, Hokkaido, Japan. The Japan Transport Safety Board (JTSB) explain in their safety investigation report (issued 18 February 2021) that the helicopter was undertaking the final of 6 hosting exercises planned for that flight. The right-hand door was opened, a rear crew member attached two connected 5lb ARS Hoist Hook Weights (a total mass of 10 lb, 4.54 kg) to the hook to increase stability and let go of the hoist hook. The weights however “came off from hoist hook hole and dropped from altitude 180 ft (55 m)”. They were subsequently found in the national forest near the airfield. They had not hit anyone but the Dropped Objects Prevention Scheme (DROPS) calculator confirms this as a potentially fatal incident. JTSB Safety Investigation The JTSB report that upon examination no defects were found with either the hoist hook or the attachment hook on the weights, a component also widely used on mountain-climbing gear. The investigators comment that: The weight hook can be opened by squeezing levers on the both side and remains open. When you insert an object to hook, the object pushes the guide and close the hook. The weight hook consists of two hook-shaped parts that are overlapped symmetrically and attached with a shaft, and the spring is pushing the two parts to close from both sides. When the hook is closed, the spring force is applied in a direction to close, and when it is open, the force is applied in a direction to open. When you connect the weight to the hoist hole it is difficult to visually confirm situation of the weight hook whether it is open or closed for the weight hook works inside the hole. The hook weights had only recently been purchased by the Fire Department, differed from the traditional Karabiners and had only been used “a few times”. Upon introducing the weights, rescue members conducted familiarity training to confirm their usability and installation certainty, but did not anticipate the possibility that the weight hook may be disengaged. Fortuitously video footage was available of the incident to aid the investigation. The enlargement of the hoist hook image… …shows that the lever on one side can be seen, but the other side cannot. In addition, the black upper part of the hook seems to be open on its right side. From this, it was confirmed that one side of the hook was open when the weights were released. The image above shows show that the crewmember placing their hands on the lever when attaching the weights to the hoist hook hole. The instruction manual of the hook manufacturer, describes a warning that it should never hold the lever during connection. However, when they purchased the weight[s], no manual was attached. The crew member confirmed they were aware of the need to apply tension to confirm secure attachment but unconsciously omitted that check. During testing, it was found that weights were able to hang as shown below. If the weight was put outside in this state, weights would sway to the left, and therefore, the weight hook would turn clockwise as the arrow indicates. It was confirmed due to the shape of the hook tip, the hoist...
read moreATR 72 Rudder Travel Limitation Unit Incident: Latent Potential for Misassembly Meets Commercial Pressure
ATR 72 Rudder Travel Limitation Unit Incident: Latent Potential for Misassembly Meets Commercial Pressure (Air Contractors, EI-SLG) On 15 March 2011 ATR 72-202 EI-SLG of Air Contractors experienced an uncommanded yaw, resulting in a roll to the left as it accelerated through 185 kt. Directional control was regained and aircraft returned to Edinburgh Airport. Cockpit indications identified a fault with the rudder Travel Limitation Unit (TLU). The aircraft was makings its first flight following a ‘2 Year’ base maintenance check at Edinburgh and was being positioned to Paris. In this article we examine the airworthiness aspects. System Design and Organisational Background The UK Air Accidents Investigation Branch (AAIB) explain in their safety investigation report (issued in July 2012) that: The rudder linkage on the ATR 72 is a mechanical system… The TLU, installed on the rudder rear quadrant shaft, reduces the range of available rudder deflection at airspeeds above 185 kt, in order to limit the structural loads on the rudder. In the full authority (or low speed) position, rudder deflection is not limited; in the reduced authority (or high speed) position, rudder deflection is mechanically limited by the TLU. The TLU mechanism comprises an electrical actuator which drives a pivoting bracket on which two rollers are mounted. In the reduced authority position the actuator retracts, engaging the rollers in two v‑shaped cams mounted on the rudder rear quadrant shaft, to limit the rudder deflection mechanically. In the full authority position the actuator extends, disengaging the rollers from the cams and rudder deflection is no longer limited. Within the ATR family the TLU is unique to the ATR72. The maintenance organisation that performed the check… …had previously been owned by the aircraft operator but both were now sister companies and part of a larger group. Two of the operator’s aircraft had recently experienced significant delays at the Edinburgh facility…. Another of the operator’s aircraft was planned in for maintenance immediately following EI-SLG. The management at the maintenance organisation considered that another delayed aircraft would have been viewed as a major failure on their part and would result in loss of revenue if the following aircraft could not be accommodated. Of note however is that: This operator had a policy of directly purchasing parts from the aircraft manufacturer, and forwarding them to the maintenance organisation. The maintenance organisation considered that this practice would often result in delays, causing a backlog of work towards the end of the maintenance check. During maintenance: A check leader was assigned… This role involved allocation of job cards and manpower, ordering of spares and reporting on the progress of the check. A number of mechanics and LAEs were assigned to each aircraft, and the senior LAE would deputise for the check leader in his absence. The maintenance organisation had a production manager. The production manager was an experienced [Part-66 C Licenced] engineer who had worked for the organisation for two years. In this time he had been promoted to the role of check leader and was subsequently appointed as production manager, responsible for the overall management of the maintenance facility. Noticeably: This post also entailed acting as the Accountable Manager for the company’s Part 145 maintenance organisation approval. In addition to this he also held the post of line maintenance manager. As well as the potential for high workload and distractions from these multiple roles, AAIB note that: This situation represented a conflict of interest between the production manager’s commercial priorities and his obligations as the Accountable Manager. AAIB Safety Investigation After landing… …subsequent visual inspection of the TLU confirmed that one of the cams on...
read moreS-76A++ Rotor Brake Fire
S-76A++ Rotor Brake Fire (N911FK of Trauma Star) On 16 December 2017 Sikorsky S-76A++ N911FK of Trauma Star was damaged by fire near Islamorada in the Florida Keys, shortly after completing a helicopter air ambulance flight to pick up a stabbing victim. The Fire The US National Transportation Safety Board (NTSB) explain in their safety investigation report (issued in February 2021) that… …the flight departed Florida Keys Marathon International Airport (MTH), Marathon, Florida, about 0637 for an air medical trauma patient pickup; the pilot landed at a pre-surveyed landing zone [on a sports field at the Coral Shores High School] at about 0650… The Trauma Star Part 135 General Operations Manual states that for ‘Ground Operations at Off Airport Landing Sites’: Once the aircraft has landed, the pilot will apply the rotor brake and stop the aircraft rotor system. The pilot will then advise the medical crew when it is safe to exit the aircraft. Trained medical crew will supervise the preparation of the patient for loading into the aircraft, including ensuring the patient is adequately secured to the litter, removal of any unsecured sheets or blankets from the litter assembly, etc. Ambulances may bring the patient to the aircraft but will not approach within 30 feet of the aircraft or rotor system. The pilot, who had 5850 hours of total experience, 685 hours on type,… …positioned the engine controls to idle and the main rotor speed (Nr) was less than 60% before he applied the rotor brake to stop the rotors. After the rotors stopped, the paramedic and flight nurse exited the helicopter to attend to the patient. The pilot indicated that after the medical crew departed the helicopter, he noticed that the No. 1 engine temperature was fluctuating with an increase in the inlet turbine temperature, so he shut down the No. 1 engine. The operator reported that, about the same time, the flight nurse noticed dark smoke coming out of the main rotor gearbox cowling area of the helicopter. The flight nurse reported that the smoke was accompanied by sparks, which shortly after turned into flames; she and the paramedic ran toward the helicopter and signalled the pilot about the fire. The pilot reported that he noticed the flight nurse waving her arms and warning of a fire but did not observe any cockpit indications of a fire; however, he shut down the No. 2 engine and observed flames when he partially exited the helicopter. He discharged both engine fire bottles and then exited the helicopter. He stated that the fire continued to burn until fire department personnel extinguished it. NTSB Safety Investigation The thermal damage observed in the main rotor gearbox compartment appeared centered around the rotor brake. The rotor brake control components did not exhibit evidence of anomalies that would have either led to its uncommanded engagement with rotors turning or sustained engagement after disengagement of the rotor brake. Raised material found on the rotor brake disk surface was consistent with fused material from the rotor brake pads. Both forward and aft brake pucks extended when hydraulic pressure was applied to the brake calipers. The forward pucks of the left and right brake calipers did not automatically retract when hydraulic pressure was removed, but they were manually retracted without difficulty. The NTSB note that: The rotorcraft flight manual supplement (RFMS) for the accident helicopter mentioned the possibility of a rotor brake fire if pressure has been applied to the rotor brake system that resulted in a rotor brake puck dragging against a brake disk. However, with...
read moreBEA Point to Inadequate Maintenance Data and Possible Non-Conforming Fasteners in ATR 42 Door Loss
BEA Point to Inadequate Maintenance Data and Possible Non-Conforming Fasteners in ATR 42 Door Loss (Hop! ATR 42-500F-GPYF) On 25 March 2018 ATR 42-500 F-GPYF of HOP! flew from Paris-Orly to Aurillac. At top of descent the 15 kg left Main Landing Gear (MLG) door separated from the aircraft, impacting and damaging the left-hand wing/body fairing. The aircraft was able to make a safe landing. The Accident The French Bureau d’Enquêtes et d’Analyses pour la Sécurité de l’Aviation Civile (the BEA) explain in their safety investigation report (issued in February 2021) that examination… …of the aeroplane’s left MLG door made it possible to establish that the nut of the door’s rear hinge assembly had unscrewed in service before coming off. The screw then moved backwards which allowed the male hinge to come out of the female hinge resulting in the landing gear door being slightly misaligned with the fuselage. This misalignment increased the aeroplane’s drag. The analysis of the FDR data found that the increased drag and thus the misalignment of the door was present at least from the first level flight at FL110 and that it probably did not exist on the previous flights. This abnormal position of the door also resulted in additional loads on the other landing gear door attachment points, in particular the link which failed under fatigue at the start of the descent. The loss of the link and rear hinge assembly attachment points then introduced substantial loads on the remaining main attachment point, the front hinge assembly, until failure under overload of the male hinge. Once the three main attachment points were no longer effective (link, front hinge assembly and rear hinge assembly), the door swung upwards around hinge No. 1 and struck the fuselage and window. This situation generated the noise heard and jolt felt by people on the plane followed by the failure under overload of this same hinge. The door then separated causing: damage to wing root fairings scratches to a cabin window and the surrounding skin a tear on the lower surface skin of the left flap scratches on lower surface skin of the left wing small dents on vertical stabilizer. The BEA note that: An occurrence in 2013 reported by ATR showed significant similarities… [M]aintenance had been performed on the landing gear doors shortly before the occurrence and that the job card had only been partially applied because of a shift change while the task was being performed. This could have resulted in some of the nuts on the landing gear door hinge assemblies not being tightened. Although the hinge assemblies of the main landing gear doors are not considered as critical parts, these two occurrences show that the simple loss of the nut from the rear hinge assembly can result in the loss of a main landing gear door weighing around 15 kg leading to risks for the aeroplane and also constituting a danger for people and infrastructures on the ground which cannot be ignored. There is sadly often over-enthusiasm for assuming maintenance errors have occurred due to a ‘Failure to Follow Procedures” (FFP), obsessing on classifying how and why personnel ‘violated’ those procedures and applying crude culpability decision aids. This case study shows that approach is very misguided in limiting the potential for holistic systemic improvement. Fortunately, the “sole objective” of BEA safety investigations aims “at improving aviation safety [and] does not presuppose the existence of a misdemeanour...
read moreWire Strike on Unfamiliar Approach Direction to a Familiar Site
Wire Strike on Unfamiliar Approach Direction to a Familiar Site (Air-Glaciers Airbus Helicopters AS350B3 HB-ZCZ) On 11 March 2019 Airbus Helicopters AS350B3 HB-ZCZ of Air-Glaciers struck a with a power line near the Tseuzier dam in Crans-Montana near Sion, Switzerland. The helicopter survived the wire strike with only damage to the leading edge of one main rotor blade. The Serious Incident Flight The Swiss Safety Investigation Board (SUST) explain in their safety investigation report, issued in French on 21 January 2021, that the helicopter was conveying three workers to a dam, to conduct a monthly inspection. The helicopter was equipped with a cable cutter / Wire Strike Protection System (WSPS) as well as a FLARM, a glider/GA traffic warning system that also warns of obstacles programmed in its database. The pilot said he landed at the Tseuzier dam about 50 times in total, once in the past 90 days. [However]…reduced visibility conditions forced the pilot to undertake an approach from the left bank of the dam…the first time he made this approach… Without performing a reconnaissance flight prior to the approach, the pilot intended to fly over the power line he was aware of, then perform the final approach along the dam wall. SUST note that obstacles over 25 m are required to be notified and are available via the obstacle collection system and a Web-GIS Obstacle Map (WeGOM) is updated twice per week. At the time the cable was in the database, but its position was offset by 20-50 metres as show below (since corrected but not a factor in this wire strike). The [operator’s] Operations Manual (OM) A, states that …“A direct approach is permissible provided that the surroundings are reasonably clear and or familiar and that the airspeed is adjusted to a slow enough ground speed.” According to the pilot’s statement, these conditions were met. As the pilot later stated, he was familiar with the line, but he estimated its position a little further north [consitent with the obstacle database] and at a lower altitude in the valley. The FLARM obstacle alert was not integrated into the intercom system and headset audio, so was not heard by the pilot, although it was audible in the cabin. During the approach the wire strike occurred. The pilot did not notice any vibration or engine parameters being exceeded; he continued his approach and landed the helicopter without problem on the planned landing zone. As the weather conditions deteriorated, the pilot does not stop the machine completely but only idled the engine. After a 5-minute flight back to base, damage to the leading edge of a main rotor blade was observed. No other part of the helicopter was hit. SUST Analysis The investigators concluded the pilot was familiar with the area. Although the OM A’s straight-in approach requirements were probably met, the pilot deprived himself of the ability to visually determine the exact position and height of the obstacle using a preliminary reconnaissance flight. Assuming he was familiar with the position and height of the obstacle, the pilot took an increased risk, even in good visibility conditions. The FLARM obstacle alert was on but only audible in the helicopter cabin. Consequently, the pilot did not hear the aural alert when the helicopter approached the power line. This highlights that such an installation as a last safety net is not useful if there is too much noise in the cabin. In this case, it can...
read morePrior Engine Mount Damage Lead to Fatal Aerial Saw Crash
Prior Engine Mount Damage Lead to Fatal Aerial Saw Crash (Rotor Blade LLC, Hughes / MD 369D / 500D N89ZC) On 5 March 2019 Hughes (later MD) 369D / 500D N89ZC, operated by Rotor Blade LLC, crashed near Talking Rock, Georgia, killing the pilot. This occurred during a Part 133 external load flight using a 10-bladed aerial saw to trim trees alongside power lines. The Accident and NTSB Safety Investigation The US National Transportation Safety Board (NTSB) explain in their safety investigation report that three passes were planned (upper, middle, and lower): A witness reported that the pilot performed the upper pass, then returned for the middle pass when the helicopter began to rotate counterclockwise around the main motor mast. It completed one full rotation, and during the second rotation, the helicopter impacted trees and then the ground. Post-accident examination revealed (our emphasis added)… …a fracture of the overrunning clutch outer race and cracks on three of the engine mounts. While two of the three engine mounts cracks were likely a result of impact forces, the cracks on a third [central] engine mount were likely present prior to the accident. The failure of the overrunning clutch subassembly outer race resulted in a loss of power to the main rotor system. Given the helicopter’s low altitude and airspeed at the time of the loss of power, the pilot was likely unable to successfully initiate and perform an autorotative landing. The investigation identified that: Before its installation…the overrunning clutch subassembly had been repaired, which included the installation of a new outer race. The accident helicopter operated with the overrunning clutch subassembly for about 33 flight hours until the accident occurred. Examination of the fracture surfaces revealed signatures consistent with fatigue and subsequent overload. The orientation of the crack in the circumferential plane was consistent with an anomalous bending load, such as an angular misalignment of the drivetrain, that drove fatigue crack initiation. The investigation went on to determine that… …it is likely that the damaged center engine mount was the source of the anomalous bending loads… The 100-hour/annual inspection of the engine mounts could be performed with the engine installed on the airframe, and the operator had done so; however, the presence of the engine could present difficulties for a mechanic in performing a visual inspection, particularly of the forward side of the center engine mount, where the cracks were located. Maintenance records indicated that, in the 9 months preceding the accident, the engine mounts were inspected six times with no anomalies observed. However, when the engine mount cracks may have developed and whether they would have been visible during any of the previous inspections could not be determined based on the available information. NTSB Probable Cause A fatigue failure of the overrunning clutch subassembly due to abnormal bending loads due to cracks on the center engine mount, which resulted in an inflight loss of power. Contributing to the accident was the helicopter’s low altitude and airspeed when the loss of power occurred, which precluded the pilot from successfully performing an autorotation. Previous Accidents Not discussed in this accident report but the 1981 built helicopter had suffered three previous accidents. On 6 November 2009, while operated by Extreme Helicopters, the helicopter lost engine power less than a minute after takeoff in Baxley, Georgia. It rolled over onto its left side during the subsequent autorotation and suffered substantial damage. The pilot told the NTSB this was “main fuel valve was pulled causing fuel starvation to the engine.” On 29 July...
read moreUnanticipated Yaw: Loss of Control During Landing Site Survey
Unanticipated Yaw: Loss of Control During Landing Site Survey (Airbus EC130T2, N130TG) On 3 August 2018 private Airbus Helicopters EC130T2 N130TG lost control while manoeuvring to survey a potential landing site near the Dismal River Golf Club at Mullen, Nebraska. The pilot was uninjured, but the passenger sustained serious injuries and the helicopter was substantially damaged. The US National Transportation Safety Board (NTSB) explain in their safety investigation report that the 61-year-old pilot had just 213 total flying hours, 80 as PIC and 194 on type. The pilot reported the weather was clear and breezy with 15 to 20 knots of wind from the southeast. As the helicopter approached the golf course the helicopter was about 500 ft above the ground, 100 knots, and slowing to 70 knots as he initiated a descent. Evidence from the installed Appareo Vision 1000 image, audio, and data recorder was examined by the NTSB and proved valuable in understanding the accident: The helicopter entered a right turn around a group of buildings. A flagpole visible in the video indicated that the winds were out of the south; the flag was mostly unfurled, and the flag was fully visible. After one right turn, the helicopter started a left turn around the same group of buildings. As the turn begins to tighten in radius the helicopter starts to descend. The ground speed showed a decreasing trend with an indicated airspeed of 30 knots. The heading changed to north, the ground speed decreased, and the airspeed indicator displayed 0 knots. As the helicopter turned to a downwind condition, a left yaw rate rapidly increased and was not arrested, resulting in a loss of yaw control. The pilot stated that he initially added right-pedal during the first ½ of the turn and increased it to full right pedal for the remainder of the rotation. According to the data analysis: At the moment of loss of yaw control, the First Limit Indicator (FLI) read about 6.5 units, the pitch was nose down (about -18 degrees) and quickly became more nose down as the loss of yaw control continued. The pilot made some aft stick inputs around this time. There was a slight right pedal input observed, the right pedal was forward of the left pedal about an inch. As the loss of yaw control continued to develop, the pilot made a slight left pedal input. The helicopter continued yawing to the left and remained nose down (-18 degrees). The left pedal remained slightly forward of the right pedal until the time of ground impact. From the time of the loss of yaw control, the helicopter completed about 1.25 rotations to the left until ground impact. The fuselage and main rotor were damaged on impact. Reflectively, the pilot commented that… …he needed to perform higher, faster, and wider turns. He told the NTSB he “had encountered similar rotations before but was always able to recover”. The pilot was not familiar with the service letter from Airbus [see Safety resource below]. He had completed their course in May at their facility in Grand Prairie, Texas, and he recalled discussion regarding loss of tail rotor control. NTSB Probable Cause The pilot’s inadequate and incorrect anti-torque pedal application during a tight, decelerating turn downwind, which resulted in a loss of yaw control. Safety Resources: Unanticipated Yaw NTSB note that: In February 2005, Eurocopter released Service Letter No. 1673-67-04 “Reminder concerning the...
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