NTSB Details Fatal Yosemite Helicopter Accident

A firefighting helicopter involved in a fatal accident in Yosemite National Park last month experienced problems with its water bucket earlier in the day, according to a preliminary report released by the National Transportation Safety Board. The Airbus AS332 L1 Super Puma was conducting water drops on the Dome Fire on Sept. 20 when the accident occurred, killing both pilots aboard. The cause of the accident remains under investigation.

Earlier that day, the helicopter completed more than 25 water drops during a 2.9-hour firefighting flight over Yosemite. The aircraft was carrying an 800-gallon Nomad bucket suspended from a 200-foot longline. According to investigators, the crew experienced problems with the bucket during the flight. After the helicopter returned to its helibase, mechanics tightened the bucket’s air pressure regulator and performed a pressure check before the aircraft departed for another firefighting assignment.

Final Water Drop

The helicopter departed its helibase around 1:28 p.m. and completed two water drops near helispot H-5 after collecting water from Ostrander Lake. During the third Yosemite drop, which began at approximately 1:56 p.m., the bucket emptied in about three seconds before the helicopter yawed to the left. Investigators determined from flight-tracking data and video recordings that the helicopter’s groundspeed decreased to approximately 4 knots as its descent rate reached 1,344 feet per minute.

“The bucket appeared to drop almost vertically and then contacted the ground about 1356:38,” the NTSB stated.

The helicopter’s cargo hook released the longline approximately one second later, and the aircraft appeared to move forward. Investigators reported that the helicopter struck trees about five seconds after the bucket contacted the ground. The wreckage came to rest on sloping, forested Yosemite terrain at an elevation of approximately 8,150 feet.

Investigation Continues

Investigators located the bucket about 90 feet from the main wreckage and found the cargo hook in its locked position, consistent with a normal electronic release rather than a manual release. Much of the helicopter was consumed by a postimpact fire, leaving extensive damage to the cockpit and instruments.

The NTSB recovered and downloaded the cockpit voice recorder and conducted a preliminary analysis of engine and rotor speeds using audio from ground video recordings. Additional examination of the wreckage is planned as conditions permit. The agency has not determined what caused the helicopter to descend into the trees.