WPR16FA072

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.

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. H