Honolulu, HI, USA
N80918
BELL 206B
The commercial pilot of the helicopter was performing a local air tour around the island with four passengers onboard. During the flight, he noticed a vibration throughout the cabin. The pilot diverted toward the destination airport; however, when the vibration stopped shortly thereafter, he decided to initiate a turn so the passengers could see a nearby landmark. The vibration returned shortly thereafter, and the pilot began to maneuver toward the destination airport a second time. The pilot stated that the vibration developed into a grinding sensation, which was followed by illumination of the main rotor low rpm warning light and an increase in engine rpm to the point where the engine and rotor RPM needles were no longer matched on the power turbine gauge. The pilot initiated an approach to a grassy area near the shoreline; however, due to the presence of people nearby, he turned the helicopter slightly left to land in the water as close to shore as possible. The pilot said that, about 20 ft above the water, it felt like the main rotor stalled, the helicopter lost lift, and it "fell out of the sky." The helicopter descended rapidly into the water and sank about 20 ft from the shoreline. Three of the passengers were able to egress the helicopter following impact; however, the middle aft seat passenger was trapped inside. A first responder stated that he and another person repeatedly dove underwater to cut the passenger's seatbelt straps and extract him. The first responder reported that the passenger's life preserver appeared to be entangled with the seatbelts. Postaccident examination of the life preserver revealed signatures of inflation and cut waist straps, with no other damage noted. It could not be determined when or how the life preserver was inflated; the first responder could not recall whether it was inflated and the nurse providing CPR said it was not inflated. Review of treatment records for the passenger revealed evidence consistent with drowning, and no traumatic injuries to the head or neck. It could not be determined whether the passenger was unable to extricate himself from the restraint, or if he had a period of unconsciousness resulting from the impact that contributed to his drowning. The helicopter's doors were not installed at the time of the accident and all five seat restraints were found to be in working order and undamaged. Postaccident examination of the helicopter revealed that the engine-to-transmission drive shaft was separated at the transmission side. Metallurgical examination of the engine-to-transmission drive shaft components revealed that the forward coupling did not appear to be lubricated and that there were multiple indications of exposure to elevated temperature, such as heat tinting and loss of the temperature plates on the forward outer coupling, high-temperature cadmium-induced brittle fracture of two forward attachment bolt heads, and a loss of hardness of the bolt head material due to high-temperature tempering. The external spline teeth on the forward spherical coupling were worn down to the bottom landings, while comparatively minor wear marks were observed on the mating internal spline teeth of the forward outer coupling. The asymmetry in the wear pattern between the spherical coupling and the outer coupling combined with the observations consistent with elevated temperatures indicate that the assembly likely failed by overheating due to lack of lubrication. This resulted in softening and subsequent failure of the spring that limits and centers the spherical coupling. When the spring failed, the coupling shifted forward, damaging the forward end of the outer coupling, fracturing the forward cover plate, and wearing the external spline teeth down to the bottom landings. Following the failure of the drive shaft, the engine would have continued to operate, but would not have been able to drive the main rotor. Interviews with the pilot, the owner of the company, and a non-mechanic rated maintenance assistant indicated that maintenance had recently been conducted on the engine-to-transmission drive shaft, even though this was not recorded in the helicopter's maintenance records. In addition, the owner, who was a rated mechanic, was not present the entire time throughout the removal, inspection, and subsequent reinstallation of the engine-to-transmission drive shaft. It is likely that, when this maintenance was conducted, grease was not applied to the forward coupling as specified in the manufacturer's maintenance manual. Further review of maintenance records revealed no entries pertaining to a current annual inspection or 100-hour inspection. Additionally, a component inspection sheet provided by the operator revealed that several required component inspections were overdue and had not been completed at the time of the accident. Although the FAA was conducting oversight in accordance with their guidance, increased inspections may have uncovered the inadequate maintenance and documentation, which in turn, may have prevented the accident.
HISTORY OF FLIGHT On February 18, 2016, about 1020 Hawaii-Aleutian standard time, a Bell 206BIII, N80918, was substantially damaged when it impacted water during a forced landing near Honolulu, Hawaii. The commercial pilot and two passengers sustained serious injuries, one passenger sustained minor injuries, and one passenger was fatally injured. The helicopter was privately owned and operated by Genesis Helicopters as a commercial air tour flight under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91. Visual meteorological conditions prevailed and a company flight plan was filed for the local flight, which originated from Honolulu International Airport (HNL) about 0935. The pilot reported that, after arriving at work the day of the accident, the helicopter was pulled out of the hangar and that he began his preflight with the company's mechanic's assistant. The pilot stated that they completed "a pretty good preflight," because the flight was the first tour flight since replacement of the tail rotor drive shaft. The pilot further stated that he confirmed fuel quantity and checked other fluids before he retrieved and inspected the life preservers. The pilot then went upstairs to the company's office, met the passengers, showed them the safety video, and stored their belongings. After he boarded the passengers, whose seat positions were determined by weight and balance calculations, he put the passenger's life preservers on them and secured their seatbelts, the pilot conducted a final walkaround of the helicopter before boarding and starting the engine. After departure, the flight proceeded to fly the Shoreline 6 departure procedure to crossover to the east side of Oahu Island. The pilot then flew along the shoreline before flying toward Sacred Valley, then North Shore before turning south to fly down Central Valley, over Wheeler Army Airfield, and on to Pearl Harbor. The pilot said that, as he began the approach to Ford Island, he noticed a vibration throughout the cabin of the helicopter that seemed "different." He decided to return directly to HNL; however, the vibration stopped, and he made a left turn so the passengers could see the USS Arizona Memorial. Shortly thereafter, the vibration returned, and the pilot called the air traffic control tower at HNL to advise that the flight would be returning to the airport. The controller instructed the pilot to fly to the prison and hold for other inbound helicopters. The pilot stated that, at this point, the vibration developed into a grinding sensation. Then the main rotor low rpm warning light illuminated, and engine rpm began to rise; the point where the engine and rotor RPM needles were no longer matched on the power turbine gauge. The pilot then lowered the collective, reduced the throttle and realized the engine and main rotor were no longer connected as he began to look for a place to land; he selected the grassy area at the Pearl Harbor Memorial visitor's center. Due to his altitude, he said he tried to increase his sink rate to make the selected landing area and put the helicopter "back in trim to land" before he noticed people disembarking from the USS Arizona Memorial ferry vessel in his selected landing area. To avoid the people, the pilot turned the helicopter slightly left to land in the water as close to shore as possible, with hopes that people would come out to help. He stated that when the helicopter was about 20 ft above the water, it felt like the rotor stalled, the helicopter lost lift, and it "fell out of the sky." The helicopter descended rapidly into the water about 20 ft from the shoreline. Witnesses located at various locations at the World War II (WWII) Valor in the Pacific National Monument reported seeing the helicopter at a low altitude before it suddenly descended into the water. A review of video captured by a witness revealed that the helicopter was approaching the Contemplation Circle area of the World War II Valor in the Pacific National Monument. The helicopter's forward airspeed appeared to decrease, the nose pitched up, and the helicopter began to rotate to the left in a slightly nose-up attitude then descended rapidly into the water. At the time of impact, the helicopter appeared to be in a slightly nose-high, left bank attitude. PERSONNEL INFORMATION The pilot held a commercial pilot certificate with rotorcraft-helicopter and instrument helicopter ratings. In addition, the pilot held a flight instructor certificate with a rotorcraft-helicopter rating. The pilot held a Federal Aviation Administration second-class medical certificate issued on November 6, 2015, with no limitations. The pilot reported that he was unable to locate his logbook after he was released from the hospital; he estimated that at the time of the accident, he had accumulated about 900 total hours of flight experience, with 151 hours in the accident helicopter make/model and 125 hours within the previous 90 days. AIRCRAFT INFORMATION The accident helicopter was a Bell Helicopter model 206, serial number 2687. The helicopter was powered by a Rolls-Royce Allison model 250-C20B turboshaft engine, serial number CAE-832146, with maximum takeoff and maximum continuous power ratings of 420 shaft horsepower. The helicopter was not equipped with an emergency float system. Figure 1: Helicopter Seating Diagram The helicopter was equipped with 5 seats, two in the front, and 3 in the aft section of the cabin. The helicopter is flown from the front right seat, with passenger seating in the remaining seats as referenced in figure 1. According to Bell Helicopter Textron (BHT) representative, an integral part of the helicopter's power train system is the engine-to-transmission drive shaft, located between the transmission and freewheeling drive. The drive shaft (as installed) is comprised of two identical couplings, which are located on either end of the shaft. The internal components consist of two flanges positioned on the ends of the tubular, hollow drive shaft. The assembly requires a retainer ring and packing seal to be positioned against the flange. A drive shaft coupling seal is situated against the packing seal, impeding grease from egressing the coupling assembly. Figure 2: Engine-to-transmission-driveshaft diagram. The drive shaft contains a gear sprocket affixed to the shaft flange via 4 bolts (bolt heads positioned on the inside of the coupling). The donut-shaped gear has a hollow area in the middle that aligns with the hollow tube situated between the couplings; a slight lip surrounds the hollow area. The outer coupling gear surrounds the drive gear where it is splined, and torque is transmitted. Inside the coupling, the assembly is equipped with a shaft centering spring. The spring (item 6 in figure 2) is positioned between the lip and the end cap of the coupling (grease retainer plate). A retainer ring and packing seal rest against the back plate. The BHT maintenance manual recommends that, before reassembly, the engine-to-transmission drive shaft couplings be hand-packed with lubricant (C-015 grease) over the top of the internal spline teeth to a depth of 0.2-0.3 inch. Maintenance Records Review of maintenance records provided by the operator revealed the following recent inspections. Table: Recent Helicopter Inspections No entries referencing a current annual inspection, current 100-hour inspection, or the recent maintenance on the engine-to-transmission drive shaft were located within the airframe and engine logbooks. The most recent maintenance entry was the replacement of a tail rotor drive shaft segment on February 17, 2016, at an airframe total time of 15,516.5 hours. Maintenance Interviews Owner of Genesis Helicopters The owner of the company held a commercial pilot certificate with a rotorcraft rating and a mechanic certificate with airframe and powerplant ratings. He reported that the accident pilot was present during maintenance of the engine-to-transmission drive shaft to observe and pass tools to the mechanics assistant. The owner stated that he witnessed the initial buildup of the shaft, then left the hangar for about an hour to an hour and a half. When he returned, the mechanics assistant had already begun installing the shaft into the helicopter. The owner recalled asking specific questions about the bolts going into the shaft, to include if there was friction on the nuts, to which the assistant responded that there was. The owner recalled that the helicopter was grounded on January 23 because the rubber seal (which is located at the base of the short shaft) had come apart, and remnants were found on the (engine) deck. Replacement parts were ordered on January 25, and the helicopter was flying again on January 28. The owner estimated that the helicopter had flown 31 hours from the time the seals on the short shaft were replaced to the time of the accident. When the owner was questioned about the timeframe of the maintenance performed on the short shaft and presented with the helicopter logbooks, he responded that he "can't find them in the logs" and that it "must not have gotten put in the logbooks." When asked what manual was utilized to conduct the maintenance on the short shaft seal, the owner stated that they used the maintenance manual from Bell Helicopters. When asked how often maintenance looked at the helicopter, the owner stated that there was a daily inspection and he was personally "laying eyes on it every night." After the last flight of the day, the helicopter would be parked outside and looked at before being placed in the hangar for the night. He said the inspection would included checking the security and mounting, checking all the fluids, and visually inspecting the rotor head, lights and seatbelts. He would also examine the grips, bolts, doublers, and the tail rotor and gearbox security and mounting. When asked if he ever looked in the area of the engine-to-transmission drive shaft, he stated that he was supposed to, but when asked if he recalled doing it, he paused before stating, "I think the last time that I laid eyes on the short shaft, trying to think back, probably 3 or 4 days before the accident. There was a span prior to [February] 18th that we hadn't been flying. We were waiting on parts for the tail rotor." The owner further reported that inspections and airworthiness directives (ADs) were not reviewed on a daily basis. The 100-hour inspection information would have been written in the manual, but there would not have been anything like a countdown to an inspection. He stated that a status sheet for inspections or AD compliance was not kept in the helicopter. When asked how pilots ensured compliance with maintenance requirements, he said they had to rely on maintenance personnel to tell them that something was due or close to being due. He said sometimes the pilots would take initiative and see in the front of the book that a 100-hour inspection had been completed. He said that if the pilot saw something unsafe or observed a maintenance issue, then they could cancel the trip on their own without his approval. He said that people who wanted to come work for him knew that he would never push them to fly. The owner provided a component status sheet on February 21, 2016. There were several items that indicated negative time remaining before an inspection was due. Several of these items were annotated with check marks; the owner indicated that these inspections had been completed, but the sheet had not yet been updated. When asked about the negative-time items that were not checked, he replied that the engine installed in the helicopter at the time of the accident was a loaner engine and that the compressor and turbine listed on the component sheet were not even in the aircraft. Those components "had gone to the shop to get all that stuff up to date." When asked about the inspections of the main rotor mast assembly and the tension torsion (TT) straps, which were overdue according to the status sheet, the owner replied that the tail rotor blade had been inspected and the TT straps had not been inspected. He said the overhaul was coming up and that they were in the process of ordering parts. His intention was to take the helicopter out of service for maintenance, which would have included the TT straps. When asked if he knew they were due at the time of the accident, he stated that he knew they were coming due, but did not know that the helicopter had flown that extensively, and did not know they were due until he printed the status sheet for the investigation. Pilot During an in-person interview with the pilot, he was asked to describe the last few maintenance issues experienced with the helicopter. The pilot recalled a vibration with the tail rotor drive shaft, which had been fixed. In addition, he recalled the helicopter going through either a 50-hour or 100-hour inspection around January 15, 2016, at which time all the panels were removed, the insides were scrubbed, and all bearings were re-greased. He said everything that had a grease nozzle or tip received grease. He recalled one of the hanger bearings on the tail rotor drive shaft had loosened, which was found on the 100-hour inspection. When asked about the engine-to-transmission shaft, he recalled the short shaft seal failing and its subsequent replacement, but he could not recall the date of the replacement. He said the rubber boot from the short shaft had unseated and grease had slung around inside the panel. He recalled that the owner called him on a Saturday to inform him that flying for Monday had been cancelled so the boot could be replaced. The pilot stated that he was present when the work was being done on the short shaft seal and that the owner of the company was teaching the maintenance assistant how to press the seals. While the work was being done, the owner was quizzing the maintenance assistant. He remembered the owner and assistant referring to the maintenance manuals. Toward the end of January, he watched the owner grease the engine-to-transmission drive shaft and saw the splines on the gear when the work was being accomplished. Mechanic's Assistant The mechanics assistant, who had been employed with Genesis Helicopters for 8-9 years, did not hold a Mechanics Certificate with airframe or powerplant ratings. He reported that the "short shaft" had been removed due to leaking grease on January 25. Once they had received the new parts and the short shaft was removed, stripped down, and cleaned, the owner of the company inspected everything before reassembly. The assistant stated that, during the reassembly, one half of the engine-to-transmission drive shaft was put back together, followed by the other half. Once the work was completed, they conducted an engine run-up, a leak check, and a test flight before returning the helicopter to service. The assistant recalled that, during the installation of the short shaft, the accident pilot was present. Although the owner of the company was not present the entire time, he was checking the process and quizzed him on the parts and the type of grease used, and he was present to verify that the proper amount of grease was used before installing the shaft. The assistant further reported that he had re-used the same nuts, bolts, and washers to reassemble and reinstalled the short shaft. METEOROLOGICAL INFORMATION A review of recorded data from the HNL automated weather observation station, located about 3 miles southeast of the accident site, revealed the conditions at 0953 included wind from 050° at 12 knots with gusts to 18 knots, visibility 10 statute miles, few clouds at 3,200 ft, scattered clouds at 4,100 ft, temperature 26°C, dew point 13°C, and an altimeter setting of 30.13 inches of mercury. WRECKAGE AND IMPACT INFORMATION Examination of the accident site revealed that the helicopter was submerged about 40 ft under water about 20 ft from the shoreline. The helicopter was removed from the water the day following the accident and was subsequently rinsed with fresh water. The wreckage was moved to a secure location for further examination. Examination of the recovered wreckage revealed that t
The in-flight failure of the engine-to-transmission drive shaft due to improper maintenance, which resulted in low main rotor rpm and a subsequent hard landing to water.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
