A firefighting helicopter yawed left just after releasing water over the Dome Fire, and its bucket fell nearly straight down before the aircraft struck trees seconds later, according to a preliminary National Transportation Safety Board report on the Sept. 20 crash that killed two pilots in Yosemite National Park.
The aircraft and crew
Pilots Greg King, 56, of Alaska, and Ryan Cutter, of Park City, Utah, died on Sept. 20 at 1:56 p.m. when their Airbus AS332L1 Super Puma crashed southeast of Ostrander Lake, according to their employer, Fly Precision, an Oregon contractor. The helicopter was working under a U.S. Forest Service contract.
Some hours earlier, the same pilots had conducted a “2.9 hour firefighting flight” on a water dropping mission from a 800 gallon bucket connected to a 200 foot longline.
After 25 drops and a full fuel cycle, as they were flying back to their helibase, they encountered an issue with the water bucket.
Upon landing, according to the report, “the mechanics tightened the bucket’s air pressure regulator and pressure checked the system.”
Soon after, they were requested to conduct another water dropping mission on fires close to helispot H-5 while using Ostrander Lake as their dip site.
At 1:28 p.m. the aircraft left helibase to perform the water dropping at the designated area and flew to the dip site to fill up the water bucket to a “less than full” degree, according to the report.
Then, pilots flew about 2.25 nautical miles away from their designated drop zone and then released the water on a continuous line while flying forward at around 1:45 p.m. before returning to the Ostrander Lake.
Upon returning to the dip site, they once again filled up the bucket and went to the drop site. At roughly 8,690 feet, it began descending to drop on a dead tree while ground crew signaled with a strobe light to help the pilots localize the spot.
At 1:50 p.m. they successfully executed the drop, while maintaining a safe clearance altitude above the top of the forest line.
The helicopter returned to the dip site, the pilots filled the bucket and flew back to the drop area. Its ground speed generally decreased as its descent rate increased, the report said. The ground crew said the water was dropped in the same place as the second drop, which they considered the desired location.
Final seconds
The third water drop began at about 1:56 p.m. The bucket was empty about three seconds later and the helicopter yawed left about a second after that.
At 1:56.37 p.m. its ground speed was four knots and it was descending at about 1,344 feet per minute, according to ADS-B flight-tracking data cited in the report.
The bucket appeared to drop almost vertically and hit the ground at about 1:56.38. The cargo hook released about a second later, letting the longline fall and the helicopter appeared to move forward at about 1:56.40. It hit trees at about 1:56.43, followed by the sound of impact about a second later.
What investigators found
Analysts used the sound on the ground crew’s videos to estimate the helicopter’s main rotor speed and engine speed. Rotor speed was about 102 percent at 1:56:13 and about 101 percent near the drop and engine gas-generator speed was about 90 percent before the drop, rose to 96.9 percent shortly afterward and reached about 101.2 percent.
Near the end, the rotor speed was about 96 percent, the report says. These are preliminary estimates from video audio, not recorder data.
The helicopter came to rest on its left side with its nose pointing upslope, about 500 feet downslope from the flat area of H-5 and at about 8,150 feet elevation.
The terrain was densely forested with tall fir trees, and the canopy stood about 100 to 150 feet above ground. Several trees near the wreckage were severed, consistent with the helicopter striking the canopy. Fire consumed most of the helicopter and most of the cockpit gauges yielded no meaningful data.
The bucket lay about 90 feet west-northwest of the main wreckage, next to dirt that looked disturbed from a water drop. The cargo hook was locked, which the NTSB said is consistent with a normal electronic release rather than the manual one.
The cockpit voice recorder was retained and downloaded. The wreckage is being recovered once the fire danger allows, and will be examined later.
Responses (0)