N9FH

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...