Leesburg, FL, USA
N9FH
BHI H60 HELICOPTERS LLC UH-60A
According to the operator, a new water tank and snorkel were installed on the helicopter to facilitate firefighting operations. Several days of ground testing and calibration were performed before the accident flight, which was the first flight after the water tank was installed. The purpose of the local flight was to check the operation of the fire tank system. The helicopter made six uneventful passes in front of the operator’s hangar at the airport and dropped water that was picked up from a lake adjacent to the airport. During each of these passes, the snorkel was observed to be stable. However, during the seventh pass, the snorkel was swinging from the helicopter. The helicopter then began to hover, released the water from the fire tank, and transitioned to forward flight, gaining altitude and airspeed. The snorkel continued to make large and slightly erratic oscillations as the helicopter climbed. Afterward, witnesses heard a loud bang, pieces of the main rotor blade and tail section separated, and the helicopter descended vertically to the ground. A postimpact fire ensued. Given the sudden change in behavior of the snorkel from a consistently stable condition in normal flight to one with large and erratic oscillations, it is likely that the tank snorkel support structure was compromised and allowed the snorkel’s oscillations to increase in such a way that the pump assembly at the end of the snorkel hose contacted the main rotor blade. The contact imparted enough energy to fracture the rotor blade at the contact point, which resulted in an imbalanced rotor system and a subsequent in-flight breakup of the helicopter. The supplemental type certificate (STC) application for the water tank and snorkel had been approved by the Federal Aviation Administration (FAA) about 1 year prior to the accident. A review of the STC application documentation revealed that the FAA had not classified the water tank and snorkel system as an external load. The structural analysis of the tank used the incorrect weight of the snorkel hose and pump combination and did not account for operational loads that would be imparted into the tank by the snorkel as called for in the certification basis in the project-specific certification plan (PSCP). Testing of the snorkel and pump loads did not incorporate the water tank structure to which the snorkel was attached. The system safety analysis did not address the hazard of the snorkel contacting the main rotor system. Increased consideration in any of these areas could likely have identified design insufficiencies. In addition, the production tank that was used during flight testing was examined after the accident. A manual load test was performed with the snorkel attached to the tank snorkel support structure. When the snorkel was pulled manually from the tank, the tank structure between the hose coupler and the tank face deformed between 0.03 and 0.05 inches. These manual loads represented only a small fraction of the loads that the tank snorkel support structure would experience during normal operation. Thus, the documentation that supported the FAA’s approval of the STC was insufficient because it failed to consider the failure scenario that occurred during the accident.
Aviation Investigation Final Report Location: Leesburg, Florida Accident Number: ERA21FA233 Date & Time: May 25, 2021 17:47 Local Registration: N9FH Aircraft: Bhi H60 Helicopters Llc Uh-60A Aircraft Damage: Destroyed Defining Event Collision with terr/obj (non-CFIT) Injuries: 4 Fatal Flight Conducted Under: Part 91: General aviation - Flight test Analysis According to the operator, a new water tank and snorkel were installed on the helicopter to facilitate firefighting operations. Several days of ground testing and calibration were performed before the accident flight, which was the first flight after the water tank was installed. The purpose of the local flight was to check the operation of the fire tank system. The helicopter made six uneventful passes in front of the operator’s hangar at the airport and dropped water that was picked up from a lake adjacent to the airport. During each of these passes, the snorkel was observed to be stable. However, during the seventh pass, the snorkel was swinging from the helicopter. The helicopter then began to hover, released the water from the fire tank, and transitioned to forward flight, gaining altitude and airspeed. The snorkel continued to make large and slightly erratic oscillations as the helicopter climbed. Afterward, witnesses heard a loud bang, pieces of the main rotor blade and tail section separated, and the helicopter descended vertically to the ground. A postimpact fire ensued. Given the sudden change in behavior of the snorkel from a consistently stable condition in normal flight to one with large and erratic oscillations, it is likely that the tank snorkel support structure was compromised and allowed the snorkel’s oscillations to increase in such a way that the pump assembly at the end of the snorkel hose contacted the main rotor blade. The contact imparted enough energy to fracture the rotor blade at the contact point, which resulted in an imbalanced rotor system and a subsequent in-flight breakup of the helicopter. The supplemental type certificate (STC) application for the water tank and snorkel had been approved by the Federal Aviation Administration (FAA) about 1 year prior to the accident. A review of the STC application documentation revealed that the FAA had not classified the water tank and snorkel system as an external load. The structural analysis of the tank used the incorrect weight of the snorkel hose and pump combination and did not account for operational loads that would be imparted into the tank by the snorkel as called for in the certification basis in the project-specific certification plan (PSCP). Testing of the snorkel and pump loads did not incorporate the water tank structure to which the snorkel was attached. The system safety analysis did not address the hazard of the snorkel contacting the main rotor system. Increased consideration in any of these areas could likely have identified design insufficiencies. In addition, the production tank that was used during flight testing was examined after the accident. A manual load test was performed with the snorkel attached to the tank snorkel support structure. When the snorkel was pulled manually from the tank, the tank structure between the hose coupler and the tank face deformed between 0.03 and 0.05 inches. These manual loads represented only a small fraction of the loads that the tank snorkel support structure would experience during normal operation. Thus, the documentation that supported the FAA’s approval of the STC was insufficient because it failed to consider the failure scenario that occurred during the accident. Probable Cause and Findings The National Transportation Safety Board determines the probable cause(s) of this accident to be: The failure of the water tank snorkel support structure, which allowed the snorkel to contact the main rotor blades. Contributing to the accident was insufficient Federal Aviation Administration oversight of the supplemental type certificate process for the water tank and snorkel. Findings Aircraft (A1) Equip attach fittings (on fus) - Failure Organizational issues (A1) Oversight of reg compliance - FAA/Regulator Factual Information History of Flight Maneuvering-low-alt flying Collision with terr/obj (non-CFIT) (Defining event) Maneuvering-low-alt flying Part(s) separation from AC Maneuvering Miscellaneous/other On May 25, 2021, about 1747 eastern daylight time, a BHI H60 Helicopters LLC, UH-60A, N9FH, was destroyed when it was involved in an accident near Leesburg International Airport (LEE), Leesburg, Florida. The pilot, copilot, and two crewmembers were fatally injured. The helicopter was operated as a Title 14 Code of Federal Regulations (CFR) Part 91 post-maintenance test flight. According to the operator, 8 days before the accident, a new water tank and snorkel were installed on the helicopter, in accordance with supplemental type certificate (STC) SR00933DE, to facilitate firefighting operations. Several days of ground testing and calibration were performed before the accident flight, which was the first flight after the water tank and snorkel were installed. The purpose of the local flight was to check the operation of the fire tank system, which included the new water tank and snorkel. The helicopter made six uneventful passes in front of the operator’s hangar at LEE and dropped water that was picked up from a lake adjacent to the airport. On the seventh pass, an employee of the operator noticed that the snorkel was swinging. He called the LEE air traffic control tower and told the controller to ask the pilot to slow down and land immediately. Before the controller could contact the pilot, the helicopter transitioned to forward flight, gaining altitude and airspeed. The employee noticed that the snorkel was “violently” swinging, and he heard a loud bang. The employee saw pieces of the helicopter, including the tail section, separate from the helicopter. Afterward, the helicopter started to spin and descended below the tree line. The employee then heard an explosion and saw smoke rise above the tree line. According to another employee of the operator, she did not observe the helicopter’s first pass but watched the next six passes. She noted that the water being dropped from the tank was “very dirty.” During the helicopter’s last pass, this employee noticed that the snorkel was swinging in a large circle and that the snorkel end came very close to the main rotor blades. She immediately started waving her arms at the pilot to try and get his attention, but the pilot did not see her. Shortly after the helicopter climbed transitioned to forward flight and gained airspeed, this employee heard a loud bang and saw multiple main rotor blades separate and hit the tail section of the helicopter. She then saw the tail section fall to the ground and the helicopter enter a flat spin. Numerous other witnesses from the operator were present at the airport during the helicopter’s flight, including some who were recording the helicopter’s practice water drops. Twenty-two video clips were provided to the National Transportation Safety Board for review; 19 clips showed the helicopter performing water drops before the accident water drop pass, and 3 clips showed the accident water drop pass. In all the video clips before the accident pass, the helicopter was seen flying straight and level at a constant airspeed and releasing water over a specific point in the airport infield. As the helicopter approached the water release area, the snorkel hose was stable off the left side of the helicopter. As water was released from the water tank, the water was seen impinging on the snorkel hose, and the hose remained stable. In all the video clips showing the accident water drop pass, the snorkel hose made large and slightly erratic oscillations as the helicopter approached the water drop area. The helicopter began to hover and released the water from the tank, and the water impinged on the hose. None of the 22 video clips showed the helicopter’s transition to forward flight or climbout immediately before the accident. A security video camera mounted to a hangar that faces runway 3 captured the helicopter accident after it dropped off the water supply and proceeded down the runway heading. The video showed the helicopter flying away from the camera in level flight. The helicopter yawed suddenly, started to rotate around its vertical axis, and broke apart. The helicopter then descended vertically into the wooded area beside the runway. The behavior of the snorkel could not be observed in the video. Pilot Information Certificate: Commercial Occupant #1; Commercial Occupant #2 Age: 35, Male Occupant #1; 35, Male Occupant #2 Airplane Rating(s): Single-engine land Occupant #1; Single-engine land Occupant #2 Seat Occupied: Left Occupant #1; Right Occupant #2 Other Aircraft Rating(s): Helicopter Occupant #1; Helicopter Occupant #2 Restraint Used: 4-point Occupant #1; 4-point Occupant #2 Instrument Rating(s): Helicopter Occupant #1; Helicopter Occupant #2 Second Pilot Present: Yes Instructor Rating(s): Helicopter Occupant #1; None Occupant #2 Toxicology Performed: Yes Occupant #1, Yes Occupant #2 Medical Certification: Class 1 Without waivers/limitations Occupant #1; Class 1 Without waivers/limitations Occupant #2 Last FAA Medical Exam: January 21, 2021 Occupant #1; January 21, 2021 Occupant #2 Occupational Pilot: Yes Occupant #1; Yes Occupant #2 Last Flight Review or Equivalent: December 9, 2020 Occupant #1 Flight Time: 4873 hours (Total, all aircraft), 1344 hours (Total, this make and model) Occupant #1; 2135 hours (Total, all aircraft), 2135 hours (Total, this make and model) Occupant #2 Aircraft and Owner/Operator Information Aircraft Make: BHI H60 HELICOPTERS LLC Registration: N9FH Model/Series: UH-60A Aircraft Category: Helicopter Year of Manufacture: 1981 Amateur Built: [SAFTIAmateurBuilt] Airworthiness Certificate: Restricted (Special) Serial Number: 80-23461 Landing Gear Type: Tailwheel; Seats: 4 Date/Type of Last Inspection: December 21, 2020 Continuous airworthiness Certified Max Gross Wt.: 2100 lbs Time Since Last Inspection: [SAFTITimeSinceLastInspectionHrs] Engines: 2 Turbo shaft Engine #1: ; 2 Turbo shaft Engine #2: Airframe Total Time: 6603 Hrs as of last inspection Engine Manufacturer: GE Engine #1: ; GE Engine #2: ELT: Installed Engine Model/Series: T700-GE-701D Engine #1: ; T700-GE-701D Engine #2: Registered Owner: BRAINERD HELICOPTERS INC Rated Power: [SAFTIEngineRatedPower] Operator: BRAINERD HELICOPTERS INC Operating Certificate(s) Held: Rotorcraft external load (133), On-demand air taxi (135) Operator Does Business As: Fire hawk Operator Designator Code: [SAFTIOperatorDesignatorCode] Blackhawk Mission Equipment’s STC for the internal water tank and snorkel installation on the UH-60A helicopter was approved on May 21, 2020, by the Federal Aviation Administration’s aircraft certification office (ACO) in Denver, Colorado. Meteorological Information and Flight Plan Conditions at Accident Site: Visual (VMC) Condition of Light: Day Observation Facility, Elevation: LEE, 75 ft msl Distance from Accident Site: 1 Nautical Miles Observation Time: 17:53:00 Local Direction from Accident Site: 157° Lowest Cloud Condition: Clear Visibility 10 miles Lowest Ceiling: None Visibility (RVR): [SAFTIVisualRangeFT] Wind Speed/Gusts: 8 knots / Turbulence Type Forecast/Actual: None / None Wind Direction: 170° Turbulence Severity Forecast/Actual: N/A / N/A Altimeter Setting: 30.15 inches Hg Temperature/Dew Point: 32°C / 16°C Precipitation and Obscuration: No Obscuration; No Precipitation Departure Point: Leesburg, FL Type of Flight Plan Filed: Company VFR Destination: Leesburg, FL Type of Clearance: VFR Departure Time: [SAFTIDepartureTime] Type of Airspace: Class D Airport Information Airport: LEESBURG INTL LEE Runway Surface Type: Asphalt Airport Elevation: 75 ft msl Runway Surface Condition: Dry Runway Used: 13 IFR Approach: None Runway Length/Width: 6300 ft / 100 ft VFR Approach/Landing: Traffic pattern Wreckage and Impact Information Crew Injuries: 2 Fatal Aircraft Damage: Destroyed Passenger Injuries: 2 Fatal Aircraft Fire: On-ground Ground Injuries: N/A Aircraft Explosion: On-ground Total Injuries: 4 Fatal Latitude, Longitude: 28.817965°, -81.80863° estimated The wreckage was located in a localized swamp approximately 1,000 ft southeast from the approach end of runway 3. The wreckage was contained in a 31-ft diameter impact crater and had been consumed by fire. Section of all four rotor blades were contained with the main wreckage. The tail rotor remained attached to the vertical stabilizer and was located about 150 ft north-northeast of the main wreckage. Parts of the newly installed water tank and snorkel assembly were found on the west edge of runway 3. The water pump housing, which was installed near the snorkel inlet, was heavily fragmented. The stainless-steel snorkel suction cage was located about 50 ft west of runway 3 along with a section of main rotor blade. Several pieces of fairings and light material were lodged in the top of trees along the flightpath from the edge of the tree line to the main wreckage. The landing gear, main rotor system, main rotor drive system, engines, hydraulic system, and forward portion of the tail rotor drive system were thermally damaged by the postcrash fire. Most of the cockpit, cabin, and flight controls were consumed by the postcrash fire. Portions of the water tank and snorkel hose connecting port were located next to the left main landing gear within the main wreckage. A 10-ft section of the hose assembly (not including the suction pump) was located underneath the forward left side of the fuselage. The upper hose remained attached to the tank snorkel support, and the coupler levers were in the locked position. Portions of the hose had torn away from the tank snorkel support, and the edges were melted. The suction pump and cage were not present on the end of the hose, and the recuperator and fragmented sections of the crown housing remained attached. Most of the molded front section of the tank was fragmented and was largely destroyed by fire. The snorkel port that extends out of the molded front section of the tank was recovered. Examination of the snorkel port where the metal snorkel attachment fixture (coupler) fastened to the tank snorkel port showed that the gasket between the carbon-fiber flange plate and the tank port structure had torn and separated on the aft side. All the flange fasteners were in place. Additional Information A supplemental type certification (STC) is the FAA’s approval of a major change in the type design of a product that was previously type certificated. An FAA aircraft certification office (ACO) issues the STC. Guidance for applying for and approving an STC is contained in FAA Advisory Circular (AC) 21 40A. The FAA ACO establishes a project team that generally consists of a project manager, engineers or technical specialists, flight test engineers and pilots, manufacturing inspectors, and operations inspectors. The FAA project team coordinates with the STC applicant to develop a project-specific certification plan (PSCP). Blackhawk Mission Equipment hired a program manager and numerous FAA designated engineering representatives (DER) to design the water tank and snorkel system, conduct testing, and provide associated documentation to the FAA project team. The PSCP listed the following technical disciplines involved in the STC application: structures, electrical systems, mechanical and structures systems, flight analyst and pilot, Designated Airworthiness Representative for Manufacturing, coupon fabrication, and electrical systems and equipment. The Denver ACO assigned a project officer, electrical systems engineer, structures engineer, flight test engineer, flight test pilot, and flight standards representative. Section 4 of the PSCP, titled Project Type, stated the following: This project is a Supplemental Type Certificate for 14 CFR part 29 regulations as determined by the
The failure of the water tank snorkel support structure, which allowed the snorkel to contact the main rotor blades. Contributing to the accident was insufficient Federal Aviation Administration oversight of the supplemental type certificate process for the water tank and snorkel.
Source: NTSB Aviation Accident Database
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