Summary
On May 25, 2021, at about 17:47 local time, a BHI H60 Helicopters LLC UH-60A helicopter, registration N9FH, was destroyed after a post-maintenance test flight near Leesburg International Airport (LEE), Leesburg, Florida. The pilot, copilot, and two crewmembers were fatally injured. The helicopter was operating under 14 CFR Part 91 as a flight test.
Accident Sequence
Eight days before the accident, a water tank and snorkel had been installed on the helicopter to enable firefighting operations, in accordance with supplemental type certificate (STC) SR00933DE. After several days of ground testing, the accident flight was the first flight with the new tank and snorkel. The purpose was to check the fire tank system operation.
The helicopter made six water-drop passes in front of the operator's hangar. During these passes, the snorkel was observed to be stable. On the seventh pass, witnesses noticed the snorkel swinging. The helicopter then hovered, released water, and transitioned to forward flight. The snorkel oscillations became large and erratic. Witnesses heard a loud bang, pieces of the main rotor blade and tail section separated, and the helicopter descended vertically. A postimpact fire ensued.
Investigation Findings
Video recordings showed the snorkel hose made large, slightly erratic oscillations during the accident pass. The helicopter yawed suddenly, rotated around its vertical axis, and broke apart. The main wreckage was found in a swampy area about 1,000 feet southeast of runway 3. Parts of the water tank and snorkel assembly, including the pump housing and snorkel suction cage, were located near the runway, along with a section of main rotor blade.
Examination of the water tank revealed that the snorkel support structure had failed. A manual load test after the accident showed deformation of the tank structure when the snorkel was pulled, indicating insufficient strength under operating loads.
Review of the STC application documentation disclosed several deficiencies. The structural analysis used an incorrect snorkel and pump weight of 100 pounds instead of the actual 137.5 pounds. The analysis considered only static vertical loads and did not account for dynamic loads such as aerodynamic, lateral, or water forces. The system safety assessment did not address the hazard of the snorkel contacting the main rotor system. The FAA had not classified the water tank and snorkel system as an external load and did not apply the relevant airworthiness standards.
Probable Cause
The National Transportation Safety Board determined the probable cause 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."