Drone collides with US Army helicopter, puts 1.5” dent in rotor

Collision at 300 feet reveals limits of “trusting the app.”

But it never arrived. After waiting 30 minutes, Tantashov assumed there had been a mechanical malfunction and that the drone had fallen into the water. He returned home.

On September 28, Tantashov received a call at work. It was an investigator from the National Transportation Safety Board (NTSB), calling to asking if Tantashov was the owner of a Phantom 4 drone. He was, he said, though he had lost it recently near the Verrazano Bridge.

Would Tantashov be surprised to learn, the investigator asked, that his drone had not crashed into the water? And that it had instead slammed into the main rotor of a US Army-operated Sikorsky UH-60M Black Hawk helicopter that was patrolling for the UN General Assembly in Manhattan? And that it had put a 1.5-inch dent in said rotor and led to the helicopter diverting back to its New Jersey base?

Tantashov was surprised, and he agreed to a one-hour interview the next day, during which the full story came out.

The UH-60M had been flying as CAVM087 (“Caveman 87”), the lead craft in a flight of two helicopters that were getting their bearings to monitor a set of “temporary flight restrictions” (TFRs) involving the UN General Assembly and President Donald Trump. The helicopters were flying low, around 300 feet, and had come down the Hudson River and turned east over the Verrazano Bridge toward Coney Island. At 7:14pm, they turned around to head back toward New Jersey.

At this point, Tantashov was recalling his drone, which had begun its return flight to his location. The helicopters encountered the drone a minute later. The co-pilot on the lead helicopter was flying when the drone came into sight, and he took immediate action. Still, the drone collided with the helicopter’s main rotor 274 feet up in the sky.

The leading edge of one of the four UH-60M rotor blades was dented, while the shattered drone bits also cracked the fairing and part of the window frame material. As the recently completed NTSB report on the incident puts it, “several [drone] components were lodged in the helicopter.” The helicopter returned to base without incident.

Tantashov was an experienced flyer; he had made 38 drone flights in the last 30 days alone and had owned two drones before the Phantom 4 involved in the collision. Back when the FAA was asking drone pilots to register, he had done so.

He also knew the rules—generally. “He stated that he knew to stay away from airports, and was aware there was Class B airspace nearby,” wrote the investigator who interviewed him. “He stated he knew that the aircraft should be operated below 400 ft.”

But Tantashov didn’t know about more detailed flight restrictions, such as the TFRs around Manhattan and Bedminster, New Jersey, where the president had been staying.

“He said that he relied on ‘the app’ to tell him if it was OK to fly,” the investigator noted. “When asked about TFRs, he said he did not know about them; he would rely on the app, and it did not give any warnings on the evening of the collision. He said he was not familiar with the TFRs for the United Nations meeting and Presidential movement.” (Both TFRs were apparently violated by the drone flight.)

But “relying on the app” can be a dicey proposition. DJI’s “GEO” system did offer some guidance on TFRs, but it was problematic; according to the NTSB, DJI responded by disabling the TFR features in GEO some time in August 2017, not restoring it until October. Thus, “relying on the app” was of limited use in September, when Tantashov made his flight. In any event, DJI stresses that GEO is only an “advisory” system and that drone pilots are responsible for knowing what restrictions exist in their areas.

The probable cause of the crash? “The failure of the [drone] pilot to see and avoid the helicopter due to his intentional flight beyond visual line of sight. Contributing to the incident was the [drone] pilot’s incomplete knowledge of the regulations and safe operating practices.”

Fortunately, no more serious damage resulted, but these sorts of incidents are likely to multiply as hobbyists and enthusiasts crowd the skies, relying on third-party software and mass-market hardware to keep everyone safe.

Enlarge / One of the drone motors and part of an arm lodged in the helicopter and recovered after flight.
NTSB

As for Tantashov, one question remains: how did the NTSB find him?

It turns out that one of the Phantom 4 motors was found in the UH-60M’s engine oil cooler fan by maintenance workers after the helicopter had returned to base. The motor was handed over to the FAA office in Teterboro, New Jersey, and from there made its way to the NTSB investigators.

The NTSB then reached out to DJI and, using the serial number still legible on the motor, was able to obtain the sales record, since Tantashov had purchased the drone directly from the manufacturer.