An ATC Assisted Sikorsky H-60 Collision (HeliStream UH-60A N160AQ and US Navy MH-60R 166583, San Diego, CA)
On 22 November 2022, civil firefighting Sikorsky UH-60A Black Hawk N160AQ (operated by HeliStream for San Diego Gas & Electric) and US Navy MH-60R Seahawk 166583 collided at Brown Field Municipal Airport (SDM), San Diego, California. There were no injuries to the 5 occupants of the two helicopters.
Damage to HeliStream Sikorsky UH-60A N160AQ and US Navy MH-60R 166583, San Diego (Credit: Operator Photos via NTSB. All Other Images from NTSB)
The US National Transportation Safety Board (NTSB) released their safety investigation report on 5 December 2024.
The Accident Flights
The NSTB explain that:
According to the pilot-in-command (PIC) of the UH-60A (callsign Copter 129), he and a second pilot were conducting night vision goggle training. ADS-B data showed that Copter 129 departed Gillespie Field Airport (SEE)…about 1741 and proceeded to Brown Field Municipal Airport (SDM)….
Copter 129’s initial contact with SDM’s tower and arrival was uneventful. SDM is in Class D airspace just one mile north of the Mexican border.
About 1748, the controller asked Copter 129 if they could accept the underrun of runway 26L for landing at their own risk, and the pilot of Copter 129 accepted the underrun.
Copter 129 crossed the airport midfield, at or above 2,000 ft mean sea level (msl), and entered the left traffic pattern for landing.
At, 1753:50 the controller instructed Copter 129 to continue in the left closed pattern due to traffic, which the pilot read back.
Copter 129 arrived at the underrun, then took off, flew one circuit, and landed again on the underrun of 26L.
Meanwhile, the MH-60R (initially using the callsign Navy 410) made their initial contact with SDN tower at 1754 while they were about 5 miles west of the airport.
The controller instructed Navy 410 to enter the downwind for underrun runway 26L. The pilot read back “left downwind for runway 26L.” The controller then asked if they could accept the underrun at their own risk. The pilot responded with “affirmative.”
About 30 seconds later, the controller cleared Copter 129 for the option to land on the runway 26L underrun and the pilot acknowledged the instruction. About 1756, the controller informed Navy 410 that they were number 2 following a helicopter on short final for the runway 26L underrun, then cleared Navy 410 for the option to land on the runway 26L underrun, and instructed them to make left closed traffic.
Navy 410 stated they had the traffic in sight. The controller further instructed Navy 410 to maintain visual separation from the helicopter on the underrun. The pilot responded that they “copied all.”
Confusingly at about 1756, Navy 410 began to use the callsign Seahawk 410.
About 1757, according to the controller, he saw that Seahawk 410 appeared to have turned to their base leg early.
He then instructed Copter 129 that he needed them “on the go.” The pilot responded with, “Copter 129 on the go.”
About 4 seconds later, the controller advised Seahawk 410 that, “the copter on the go was going to the left.” Seconds later, the pilot of Seahawk 410 asked the controller to repeat the instruction.
The controller then stated, “Seahawk 410 verify you’re overflying…Navy.” About 3 seconds later, the controller instructed Seahawk 410 to, “go around the northside of runway 26L.” The pilot responded, “Seahawk 4.”
According to the controller, he instructed Seahawk 410 to go around after he became nervous that they were either going to be overflying Copter 129 or were going to the other runway [runway 26R].
About 1757, Copter 129 called “Mayday, Mayday, Mayday Copter 129.”
While between 200 to 500 ft ground level (agl) above the crew of Copter 129 had seen another helicopter overhead. Copter 129 initiated maneuvers to avoid the helicopter, including lowering the collective and applying right cyclic before feeling and hearing an impact.
According to the crew of Seahawk 410, after turning to the final approach leg and aligning with runway 26L, while about 500 ft agl at about 50 knots, the controller directed them to, “go around the north side of 26L.”
While over the first half of the runway, the PIC felt the other helicopter impact them on the aft-bottom portion of their helicopter and saw debris fly up under the rotor arc. The pilot then landed on runway 26R, repositioned off the runway, and shut down the helicopter.
Copter 129 was found to have sustained substantial damage to the four main rotor blade tips, one tail rotor blade, and the vertical stabiliser. Navy/Seahawk 410 sustained substantial damage to the left side of the stabilator.
The Safety Investigation
During post accident interviews, air traffic personnel, who are Serco employee’s, explained that the underrun was a nonmovement portion of runway 26L, about 1,800 to 2,000 ft long.
It was not maintained by the airport or lit and it was used for helicopter operations without any written procedures. Furthermore the air traffic manager told investigators that runway 26L was not approved for H-60 helicopters to touch down on the runway because of a weight restriction (12,500 lbs).
NTSB had ADS-B data for the civil helicopter but not the military one. Neither helicopters appears to have had a Flight Data Recorder (FDR).
Perhaps because it occurred at an airfield with ATC related implications, this NTSB investigation appears more detailed than many non-fatal helicopter NTSB investigations.
The NSTB analysis was that:
The takeoff instructions for the first helicopter, followed by the go around instructions for the second helicopter, combined with the night conditions, likely created a scenario where the second helicopter crew lost visual contact with the first helicopter and overtook it from overhead.
The controller was concerned that the second helicopter would overfly the first helicopter but did not issue a safety alert. The lack of a safety alert likely prevented the flight crews from understanding how close the helicopters were to each other, as well as their urgent
need to take action to avoid a collision.
NTSB Probable Cause
The failure of the crewmembers of the second helicopter to maintain visual separation with the first helicopter while complying with the controller’s instruction to go around.
Contributing to the accident were the nighttime conditions and the lack of a safety alert from the controller to either helicopter.
Safety Resources
The European Safety Promotion Network Rotorcraft (ESPN-R) has a helicopter safety discussion group on LinkedIn. You may also find these Aerossurance articles of interest:
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