Fort Myers, FL, USA
N5DF
BELL TEXTRON CANADA LTD 505
The pilot, who owned the helicopter, was proceeding to a landing zone to drop off passengers. As he initiated his approach, the prevailing wind was a right, quartering tailwind. His approach was near vertical, with no forward airspeed. The helicopter began to rotate to the right, then the rotation accelerated, and the pilot was unable to maintain helicopter control. The helicopter impacted the ground and came to rest on its left side, and the pilot and all three passengers were seriously injured. The main rotor struck a reinforced concrete light pole during the impact sequence, and the main rotor hub and blades separated from the main rotor mast. This resulted in an engine overspeed and blade shedding of the free turbine blades, by design, to prevent rupture of the free turbine disk. Postaccident examination of the airframe, engine, digital engine control unit, and data from integrated avionics revealed no evidence of a preexisting mechanical malfunction or failure that would have precluded normal operation. Recorded data revealed that during the approach, engine power demand exceeded engine power available, resulting in a loss of tail rotor effectiveness (LTE), after which the pilot was unable to recover control of the helicopter.
HISTORY OF FLIGHTOn October 8, 2022, about 1802 eastern daylight time, a Bell 505 helicopter, N5DF, was substantially damaged when it was involved in an accident at Fort Myers, Florida. The private pilot and three passengers received serious injuries. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. The pilot, through his attorney, reported that he was approaching a landing zone (LZ) at Fire Station 75 in Fort Myers to drop off passengers. About 150 ft above the ground, he noticed flags near the LZ and elected to go around to make another approach to better align with the light wind. He added power to initiate the go around and suddenly there was a “bump and dip” in the tail which was immediately followed by severe and massive vibration and shaking of the helicopter, with an uncommanded left yaw. The helicopter then pitched up and rolled violently. The pilot was unable to regain control and the helicopter impacted the ground near the LZ, in a ditch. There was no fire. The left, rear seat passenger video-recorded the final portion of the flight with a personal electronic device. The video was analyzed by a National Transportation Safety Board (NTSB) Onboard Image Recorder Group on November 15, 2022. About 43 seconds elapsed time (00:43) into the video, the helicopter was observed proceeding toward the accident site. The wind was generally out of the northeast, blowing toward the southwest. About 00:57, the camera panned inside the cockpit. The cockpit instruments appeared normal with no indication of an anomaly or malfunction. The accident site and LZ were visible ahead of the helicopter. The helicopter’s heading was about west-northwest. Flags on a flagpole were erect and indicated wind blowing from the north-northeast. At 01:32 elapsed time, the video captured the pilot. He was wearing his shoulder harness and the primary flight display showed no anomalies. The helicopter began the descent to land and slowed to near zero forward airspeed as it was above the accident site (a nearly vertical approach). At 01:41, with nearly zero forward airspeed, the wind direction relative to the helicopter’s nose indicated a right, quartering tailwind. Two seconds later, at 01:43, with zero forward airspeed, the helicopter began yawing to the right, and then the right yaw accelerated. At 01:47, the helicopter had completed 1 full rotation to the right. For the next few seconds, the pilot attempted to regain control of the helicopter as it continued to rotate; however, he was unsuccessful. The helicopter crashed and eventually came to rest on its left side after contacting trees and a reinforced concrete light pole. The engine continued to run after impact. First responders assisted the occupants out of the helicopter. PERSONNEL INFORMATIONThe pilot, who owned the helicopter, completed the Bell Training Academy 505 Ground and Flight Refresher on May 16 and 17, 2022 at Hurst, Texas. On May 18, he completed the 505 Inadvertent IMC and Helicopter Upset Recovery Course, also at the Bell Training Academy. AIRCRAFT INFORMATIONThe helicopter was manufactured in 2021. The last maintenance entry in the helicopter’s records was a lubrication service on July 7, 2022, at a total aircraft time of 182 hours. METEOROLOGICAL INFORMATIONReported surface wind at 1753 at Page Field Airport (FMY), Fort Myers, Florida, located about 6 nautical miles (nm) northeast of the accident site, was from 060° at 11 knots. Concurrently, Southwest Florida International Airport (RSW), Fort Myers, Florida, located about 10 nm east-northeast of the accident site, reported wind from 050° at 10 knots. AIRPORT INFORMATIONThe helicopter was manufactured in 2021. The last maintenance entry in the helicopter’s records was a lubrication service on July 7, 2022, at a total aircraft time of 182 hours. WRECKAGE AND IMPACT INFORMATIONAn inspector with the Federal Aviation Administration responded to the accident site and examined the wreckage. The helicopter sustained substantial damage to the main rotor, with the outboard sections of the blades separating during impact. The main rotor hub and blade assembly separated from the main rotor mast. The tail boom broke free of the fuselage and the tail rotor separated from the tail boom. There were several trees and a reinforced concrete light pole that were struck during the impact sequence. Damage to the main rotor blades showed signatures consistent with contact with the light pole. The wreckage was recovered to an aircraft salvage facility where a follow-up examination was performed. No preimpact anomalies were found with the fuel system, hydraulic system, main rotor and drive, tail rotor and drive, and flight controls. The transmission chip detectors and tail rotor gearbox chip detector were normal in appearance. The engine was shipped to the manufacturer’s facility for examination. The examination revealed no preimpact anomalies. Continuity was confirmed through the entire gear train of the module 1 (MO1). The module 2 (gas generator) was disassembled down to the high pressure turbine. The free turbine blades had shed during overspeed protection and were contained by the shroud and protection ring. This blade shedding is by engine design to prevent the free turbine disk from bursting in the event of an overspeed, as was the case in this event when the main rotor separated from the mast during impact. The free turbine nozzle guide vane sustained damage during the blade shedding. The disk could still be rotated by hand. The rotating assembly of the gas generator could not be rotated by hand. The thermocouples were removed and all exhibited thermal damage. The high pressure turbine blades all exhibited extreme thermal damage and were partially consumed. The digital engine control unit (DECU) was examined at the manufacturer’s facility, and the Garmin G1000 integrated flight deck was examined at the NTSB Vehicle Recorders Laboratory. Both units revealed the helicopter’s components operated as designed during the flight and accident sequence. During the rapid, uncontrolled descent, the data showed the collective position was raised and corresponding parameters, such as torque and Nr (main rotor rpm) changed correspondingly in an expected response. The DECU dump file captured the accident flight. The data showed that engine operation was nominal until about 30 seconds prior to the end of the recording. During the approach to landing, about 7 seconds prior to initial ground impact, collective was added and the gas generator reached the DECU TOP (take off power) embedded limit of 101.29%. The collective continued to hold the high pitch demand and the N2/Nr (power turbine speed/main rotor speed) began to droop, reaching 93.7513% about 3 seconds prior to initial impact. The collective was then lowered and the Nr began to recover at 96.68102%; however, in the next second, the collective was raised again and the Nr drooped to 87.8914% about 1 second prior to initial ground impact. At about initial ground impact, the collective was completely lowered and Nr was at 89.64968%. Nominal Nr was 104%. After initial ground impact, Nr increased to 102.5405% and collective was raised again. About 2 seconds after initial ground impact, Nr abruptly went to zero, consistent with Nr sensor impact damage. Several faults began to appear on the DECU as the unit switched to degraded mode. About 6 seconds after initial ground impact, N2 was at 124.2205%, consistent with the physical evidence of the rotor mast shearing during the impact sequence followed by the power turbine overspeed protection blade shedding. ADDITIONAL INFORMATIONThe NTSB published a Safety Alert in March, 2017, on the hazards related to loss of tail rotor effectiveness. The alert included the following information: “In helicopters, loss of tail rotor effectiveness (LTE), or unanticipated yaw, is an uncommanded rapid yaw that does not subside on its own accord. LTE can occur in all single-engine, tail rotor-equipped helicopters at airspeeds lower than 30 knots and, if uncorrected, can cause the pilot to lose helicopter control, potentially resulting in serious injuries or death. Various factors can contribute to LTE, including varying airflow from the main rotor blades (particularly at high power settings) or from the environment, which can affect the airflow entering the tail rotor; operating at airspeeds below translational lift; operating at high altitudes and high gross weights; operating near large buildings or ridgelines, which can cause turbulence; and the relative wind direction.” SURVIVAL ASPECTSAn examination of the fuselage, doors, interior, seats, and restraints, and emergency equipment revealed no evidence of preaccident anomalies or malfunctions.
The pilot’s execution of a landing approach with a right, quartering tailwind, low forward airspeed, and high power demand that, when combined, resulted in a loss of tail rotor effectiveness and helicopter control.
Source: NTSB Aviation Accident Database
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