LAX99FA136

Shortly after takeoff and transition to forward flight, the helicopter's engine stopped. During the ensuing autorotative landing glide, a main rotor blade struck a tree about 30 feet above ground level and the helicopter fell to the ground. This was the first flight of the day and the helicopter had been stored outside overnight in conditions of cold temperatures and light snowfall without engine air inlet covers installed. Prior to the flight the engine was difficult to start. There were five aborted starts before the engine was successfully started. During the first three start attempts, fuel was introduced, ignition occurred, the engine acceleration hung at 30 percent, and the starts were aborted. After the third start attempt a mechanic noted that the engine inlets were approximately half blocked by snow and cleared the snow from the inlets using a towel. He did not check the plenum chamber aft of the particle separator and forward of the engine inlet for snow. In the wreckage, the plenum chamber inspection window was found to be opaque. After the accident, another company mechanic who had dealt with the same starting difficulty on another helicopter of the same type parked under the same circumstances without inlet covers, reported finding the plenum chamber of that helicopter contained several cups of snow. The engine manufacturer reported that tests of the engine had shown that ingestion of as little as 6 ounces of snow/slush could flame out the engine. The operator's procedure requiring that the last flight crew at the end of the day install the inlet covers on aircraft stored outside had not been followed.

History of flight

On April 1, 1999, at 1136 hours mountain standard time, a Bell 206B, N992UC, was destroyed when it collided with a tree and fell to the ground during an autorotative emergency landing following loss of engine power shortly after takeoff from the Grand Canyon, Arizona, airport. Fatal injuries were sustained by the commercial pilot under instruction and serious injuries were sustained by the airline transport instructor pilot. Visual meteorological conditions prevailed for the 14 CFR Part 91 instructional flight. The helicopter was operated by Papillon Grand Canyon Helicopters and the flight was originating at the time for a local area flight.

The operator reported that the trainee pilot had recently been hired and was receiving initial new-hire training. The accident flight was the pilot's second flight in the operator's training program.

According to witnesses, the helicopter lifted off from the operator's helipad located about 800 feet northeast of the airport terminal building and transitioned to forward flight over the (public) curbside access road in front of the terminal while traveling southwest-bound parallel to runway 21. When the aircraft was over the south end of the terminal building, at 150 feet agl and flying about 50 knots, the witnesses reported that the sound of the helicopter changed. The aircraft descended straight ahead, impacted a tree with the rotor, pitched nose down, and fell to the ground near the base of the tree and along side the terminal access road.

According to the operator, the instructor pilot said that the engine had failed and the trainee pilot had entered an autorotation but struck the tree with the rotor while they were trying to reach a suitable landing site.

The operator reported that the aircraft had been stored outside overnight without engine inlet covers installed, and this was its first flight of the day. Approximately 2 to 3 inches of snow fell overnight. There were no maintenance discrepancies on the aircraft and it was flown on training flights the 3 prior days.

A mechanic's helper, who was assigned to take an auxiliary power unit (APU) to the aircraft to assist starting it, reported that there were four attempts to start the helicopter's engine using three different battery carts (APU's). After two unsuccessful attempts with the first APU, the mechanic's helper got a second APU. While he and the pilots were waiting for the batteries to charge up on the second APU, the mechanic's helper noted there was an accumulation of snow in both engine inlets. He reported to the operator that the two inlets were each one-third to one-half obstructed with snow, and that he removed approximately two handfuls of snow from each inlet and wiped snow off the particle separator with a rag. The third start attempt was also unsuccessful due to low batteries in the second APU. A third APU was then brought out and the engine start was normal. The aircraft then remained on the pad with the engine operating prior to departing.

In a telephone interview, the instructor pilot reported that he had worked for the operator since 1995 and his cold weather (snow) operating experience is limited to this time. This was his fourth winter there and he characterized the snowfall present preceding the accident as common for the Grand Canyon in winter.

Regarding the difficulty starting the helicopter, the pilot said they used three different APU's on the day of the accident for a total of six start attempts. All three APU's were battery carts, not engine driven generator type GPU's. The first three start attempts were made with the first APU. On all three attempts the engine was accelerated to 13 - 14 percent, fuel was introduced, the engine lit, acceleration hung about 30 percent, and the starts were aborted. A 30-minute wait ensued for starter motor cool down after the third attempt. The fourth and fifth start attempts used the second APU, identified as the 4X4. The batteries on the 4X4 were low and only about 10 percent N1 could be attained. No fuel was introduced on the fourth or fifth start attempt. The third APU, identified as the "Superbee," was pushed out to the meadow and the sixth start was normal. The pilot recalled that it was after the third start attempt that the mechanic's helper removed snow from the inlets.

The instructor pilot said he was aware of the flight manual limitations on operating in snow and the importance of keeping the inlets clear; however, he didn't think he nor the student pilot checked the plenum aft of the particle separator and forward of the engine inlet for snow accumulation. He definitely recalled that the inlets were clear and, after starting the engine, he checked that the swirl tubes in the particle separator were clear. He said that when the engine quit, it just went silent, there was no surge or bang.

Following the accident, another one of the operator's mechanics reported finding an accumulation of snow behind the particle separator and forward of the engine inlet on another Bell 206 on the morning of the accident. The second helicopter, like the accident helicopter, was parked in the meadow overnight without inlet covers installed. This mechanic used two heat guns to melt and dissipate the snow.

Aircraft information

The aircraft had received a 100-hour/annual inspection on February 10, 1999, and had flown 27 hours since that time. Additionally, 12-month inspection items were accomplished on March 28, 1999, and the aircraft had flown 4.5 hours since that time.

Wreckage and impact information

At the Grand Canyon airport, the terminal access road passes in front of the terminal on a northeast-southwest heading parallel to the airport's single runway, 3-21. The aircraft boarding ramp is on the opposite side of the terminal. The accident site was on the shoulder of the terminal access road on the side opposite the terminal and approximately 200 feet southwest of the terminal at the intersection with the crossroad forming the south entrance/exit for the airport. The latitude at the accident site is approximately 35 degrees 57.56 minutes north and the longitude is 117 degrees 8.10 minutes west. The airport elevation is 6,606 feet msl. The entire aircraft was present at the accident site and there was no fire.

Approximately 20 feet northeast of the accident site on the same shoulder of the road was a pine tree, which had been severed about 30 feet above ground level. The severed top of the tree was lying on the ground at the base of the tree and was about 10-inches diameter at the point where it was severed. The fracture surface was aligned 45 degrees to the axis of the tree trunk.

All of the helicopter was present in proximity of the main wreckage except the red (dot) main rotor blade, which was separated from the root section outboard of the root reinforcement doublers. The red blade was laying approximately 50 feet east of the main wreckage in the traffic lane of the south entrance/exit road that formed the intersection. The tip end 12-inches of the red blade was shattered and had small wood particles embedded in it. The trailing edge of the red blade exhibited small compression buckles along its span. The white (dot) rotor blade was laying on the ground adjacent to the fuselage and remained attached to the hub, but was bent and broken outboard of the root doublers. There were two gouges in the lower surface of the white blade, each about 6-inches long (chordwise) and 1-inch wide. The gouges were about 2 feet inboard from the tip of the blade.

The tail boom with the tail rotor assembly attached was laying about 5 feet northeast of the fuselage. The tailboom and tail rotor driveshaft were separated at the fuselage juncture with tension tearing on the lower skin and compression buckling in the upper skin. There was a 45-degree bend upward and counterclockwise in the boom at the base of t