The Kaman K-Max helicopter that crashed last month during firefighting operations in Colorado was equipped with a cockpit video recorder, providing investigators with valuable evidence as they seek to understand the cause of the fatal accident.
Pilot Nicholas Dale was killed when the helicopter crashed into Silver Jack Reservoir during firefighting operations in Colorado’s San Juan Mountains on July 12. The aircraft was being operated by Georgia-based Helicopter Express under contract to the U.S. Forest Service in support of suppression efforts on the Gold Mountain Fire.
According to a preliminary report by the U.S. National Transportation Safety Board (NTSB), the aircraft was fitted with an Appareo AIRS-400 airborne image recording system that recorded video, ambient audio, and flight parameter data from the accident flight. Although not yet mandated for all helicopters, such devices are becoming increasingly common in the industry and are required by the Forest Service under its Multiple Award Task Order Contract (MATOC) program.
On the day of the accident, the K-Max lifted from a remote helibase near Ouray shortly after 4 p.m. local time. It was equipped with a 660-gallon (2,500-liter) water bucket suspended from the helicopter by a 150-foot (45-meter) long line, which it filled from the Silver Jack Reservoir for suppression efforts on the forest fire about three miles to the southeast.
The helicopter completed five water bucket drops over the fire, each preceded by a dip at the reservoir. Cockpit video footage of these dips and drops “revealed that the pilot generally made large repetitive cyclic inputs while he maintained hover,” which were “comparable to the large cyclic inputs that were observed during the final bucket dip that immediately preceded the accident,” the NTSB report states. It describes the pilot’s control inputs as “unremarkable” while the helicopter was transiting between the dip and drop sites.
“During the final water bucket dip, the helicopter pitched up rapidly, accelerated in right yaw, and rolled right into an extreme unusual attitude,” the report continues. “A large aft cyclic movement was observed as the unusual attitude progressed and the cyclic continued moving aft until it was obscured in the field of view (FOV). The helicopter pitch then decreased rapidly, and the trees, shoreline, and water came back into the FOV.”
At the end of the video, the K-Max was in an extreme right roll with the nose falling through the horizon toward the water. A witness on the ground observed the helicopter turn right after refilling its water bucket, then descend into the reservoir upside down.
According to the report, “the portions of the video that were reviewed, which included the final sequence of events, did not reveal any abnormal sounds or vibrations indicative of a rotorcraft system or engine malfunction during the flight.”
The bulk of the wreckage was salvaged using a CH-47 Chinook helicopter on July 22, and smaller pieces of debris were found on the reservoir shoreline. The analysis of the wreckage described in the report indicates that there was substantial impact damage but no obvious engine or control abnormalities.
However, investigators recovered only minor fragments of the aircraft’s servo flaps, the rotor blade parts implicated in several previous fatal K-Max accidents. Small airfoils mounted on the trailing edge of rotor blades, servo flaps are unique to Kaman helicopters including the K-Max, which has an intermeshing rotor system consisting of twin counter-rotating, two-bladed rotor systems mounted side-by-side on individual pylons.
In most helicopter models, the pilot’s flight control inputs act on the main rotor blades, but in the K-Max, the pilot controls the servo flaps, which deflect the airstream to twist the rotor blades and change their pitch.
The failure of a servo flap is not always catastrophic, but in at least two previous fatal accidents investigators concluded that it led to contact between the left and right rotor systems and the helicopter breaking apart in flight. These include the 2021 crash of a Black Tusk Helicopter K-Max in Killam Bay, British Columbia, and the 2020 crash of a Central Copters K-Max in Pine Grove, Oregon.
The NTSB notes that the information in its report is preliminary and subject to change. The agency is probing the crash as a “Class 3” investigation, an intermediate designation that implies it will involve fewer resources than a large investigation, but an effort to identify safety issues that reveal the underlying causes of the accident.
