By TARA COPP

WASHINGTON (AP) — The crash of a Marine Corps helicopter last year that killed five service members was ultimately caused by pilot error, but the use of night vision goggles and unsafe flying conditions also likely were factors, according to an investigation report obtained by The Associated Press.

The CH-53 Super Stallion crashed Feb. 6, 2024, during a late night flight when it hit a mountain near Pine Valley, California, on its way back to Marine Corps Air Station Miramar.

Investigators found that multiple factors likely led to the crash. But as with several previous military aviation accidents, investigators had to make some assumptions because the CH-53 was not equipped with a flight data recorder capable of surviving a crash.

The limits of night vision goggles also have been identified as a potential factor in the fatal collision of an Army Black Hawk helicopter and a passenger jet near Reagan Washington National Airport in January that killed 67 people. The goggles can reduce a pilot’s ability to determine distance and can be degraded by weather or light pollution.

The Marine helicopter was flying in icing conditions with low cloud cover that obscured the mountainous terrain along the flight path. The crew was using night vision goggles, which likely did not give them the clear picture needed to avoid a crash into terrain, investigators found.

The precipitation and clouds probably degraded the goggles’ performance and possibly gave the crew a false sense that they were maintaining the safe distances needed in the flight, investigators found.

The pilot and crew chief “most likely believed they were operating legally and within their comfort level,” investigators found.

Ultimately, though, investigators found that the pilot’s failure to avoid the terrain was the primary cause of the crash. They also found that the commanding officer, who was relieved of duty due to a loss of confidence in an ability to lead, should not have given the crew approval to fly.

The Super Stallion vanished during the overnight flight on its way back to Miramar from Creech Air Force Base. The helicopter was discovered in the morning near the mountain community of Pine Valley.

All five Marines aboard were killed in the crash: Marine Corps Lance Cpl. Donovan Davis, 21, of Olathe, Kansas; Sgt. Alec Langen, 23, of Chandler, Arizona; Capt. Miguel Nava, 28, of Traverse City, Michigan; Capt. Jack Casey, 26, of Dover, New Hampshire; and Capt. Benjamin Moulton, 27, of Emmett, Idaho

In interviews contained in the report, multiple members of the squadron said that the crews had been stretched thin because their unit had to fly additional missions to compensate for last year’s monthslong grounding of the V-22 Osprey fleet.