Billings, MT, USA
N2660A
PIPER PA18A
As the airplane approached the airport, the pilot was given clearance to land on runway 28L. The pilot reported that he also heard the tower controller tell an inbound helicopter to follow him. Review of a recording of the tower communications revealed that the controller actually instructed the helicopter to pass behind the airplane and cleared the helicopter to land on taxiway H in the opposite direction of the airplane. (Taxiway H was south of and parallel to runway 28L with a taxiway centerline to runway centerline distance of about 200 feet.) About 1 1/2 minutes later, the tower controller told the airplane pilot that there was a helicopter on his left side and that it would be landing on the taxiway adjacent to the runway. The airplane pilot did not acknowledge the transmission. The airplane pilot said that he was planning to fly the airplane low over the runway and land long to expedite his ground taxi. As the airplane pilot flew low over the approach end of the runway, he was surprised to see the helicopter flying towards him. He thought it was flying over the edge of his runway and that its rotor wash would impact his airplane. However, radar data from an antenna located on the airport indicated that the two aircraft were horizontally separated by about 300 feet when they passed each other at a point about 885 feet from the approach end of the runway. Additionally, the helicopter pilot reported that his landing on taxiway H was accomplished about 300 feet from the airplane. The airplane pilot stated that just as he was passing the helicopter, his left wing tip was violently slammed down. The airplane veered right about 30 to 40 degrees, stalled, and impacted the ground. A witness observed the airplane's left wing strike the runway before the airplane veered right off the runway and over the grass. Airport operations personnel located a yellow paint transfer mark on the runway surface about 1,616 feet from the approach end of the runway. The location and paint color of the transfer mark were consistent with the airplane's left wing tip impacting the runway when the airplane's fuselage was over the runway's right edge. Radar data indicated that, at the time the airplane produced the mark, the helicopter was more than 1,350 feet away. At the time, the airplane was landing with a direct crosswind of about 6 knots from the left. The FAA Aeronautical Information Manual states that "Pilots of small aircraft should avoid operating within three rotor diameters of any helicopter in a slow hover taxi or stationary hover." Since this helicopter's main rotor disc diameter was about 33.5 feet, the recommended distance to maintain from small airplanes in order to prevent downwash encounters was about 100 feet. Additionally, a representative from the helicopter manufacturer's safety department said that a helicopter descending during air taxiing and with a forward speed of about 58 mph, the helicopter's ground speed when it passed the airplane, would produce significantly less downwash relative to what it would produce when static hovering or hover taxiing.
On August 10, 2010, about 0818 mountain daylight time, a Piper PA18A, N2660A, was substantially damaged during impact with terrain subsequent to a loss of aircraft control during landing at Billings Logan International Airport (BIL), Billings, Montana. The private pilot and his passenger received minor injuries. The airplane was being operated by 172 LLC of Park City, Montana, under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed for the personal cross-country flight, which had departed from Laurel, Montana, approximately 15 minutes before the accident. A flight plan had not been filed. According to the pilot, BIL tower cleared him to land on runway 28L. The pilot reported hearing BIL tower tell an inbound helicopter to "follow the cub," and he heard the helicopter pilot respond "traffic in sight." The pilot said he was planning to fly low down the runway in order to exit at the runway 25 intersection. The pilot said that "just as I was touching down, I saw the helicopter flying towards me. He was on the left edge of the runway, definitely not over the [parallel] taxiway." The pilot stated that, just as he was passing the helicopter, his left wing tip was "violently slammed down." He further stated that he had the flaps fully extended, which "magnified the effect of the rotor wash." He further stated that he must have added power to try and correct the problem because the airplane "broke right and hit more turbulence and at that time went out of control to the right." Next, he remembers seeing the ground rushing towards him as the airplane "slammed" into the ground at an extremely steep angle. The passenger in the airplane, who was a student pilot, said he was wearing a headset and was on intercom with the pilot. He said that as the airplane approached runway 28L for landing, the pilot lined up left of the runway centerline for landing. As the airplane passed over the end of the runway, he saw the helicopter for the first time. He thought it was over the accident airplane's left wing. The passenger said that next the airplane's left wing dipped hard, but did not touch the runway; he said it just missed the ground. He said the accident airplane "jumped" up to about 15 feet above ground level (agl) "as if rotor wash lifted it up." Next, the left wing rose up and the airplane veered to the right. Moments later, the airplane dropped steeply down with its left wing low impacting the ground with its wing tip and nose simultaneously. A witness, located at the approach end of runway 28L, observed the accident airplane flare over the approach end of the runway and proceed to fly down the runway at 10 to 15 feet above ground level (agl). He said the airplane did not touch down. The witness observed a helicopter flying in the opposite direction over taxiway Hotel, which was parallel to and south of runway 28L. At about the midpoint of runway 28L, the helicopter, which had been descending, leveled out about 10 to 15 feet agl and continued to fly east along the taxiway. The witness stated that shortly after the two aircraft passed each other the airplane made an abrupt hard left roll, with its left wing tip striking the runway. He said the airplane appeared to recover and remain in the air without his tires touching the ground. Immediately the airplane veered right and appeared to be trying to gain altitude. During this time, the airplane was rocking back and forth. A few seconds later, it appeared to stall, roll left, and strike the ground from about 20 feet agl. From what the witness could see, it appeared that the left wing and propeller spinner hit the ground simultaneously. The airplane then cartwheeled to the right wing before the tail settled to the ground. The airplane came to rest upright heading about 180 degrees from the direction that it was headed in after the initial wing strike on the runway. The helicopter pilot said the tower controller cleared him to land on taxiway Hotel and hover taxi to parking. He was established heading eastbound over taxiway Hotel at about 100 feet agl when he observed an airplane westbound on runway 28L. He continued his descent to taxiway Hotel and then hover taxied to parking. The helicopter pilot stated that "at no time did the helicopter ever hover over or around the [airplane]" and that the helicopter's "landing to a hover was accomplished approximately 300 feet from the [airplane]." The mechanic who was a passenger in the helicopter stated that they executed a right turn over the west corner of runway 10R and descended over taxiway Hotel. He stated that the helicopter "never overflew any aircraft." Review of a recording of BIL radio communications indicated that, as the helicopter approached the airport, the tower controller told the pilot of the helicopter to "pass behind [the airplane], you are cleared to land Hotel taxiway, taxi to parking." The review of the recording also indicated that when the airplane was about to turn onto final approach for runway 28L, the BIL tower controller told the pilot of the airplane that "off your left you'll see a helicopter, he'll be landing [on] Hotel taxiway." There was no acknowledgment of this transmission from the pilot of the airplane. BIL has an Airport Surveillance Radar (ASR) site located on airport property at the north end of closed runway 18/36. The ASR recorded the positions of the two aircraft about once every 4.8 seconds. The recorded data depicted the airplane landing to the west on runway 28L and the helicopter landing to the east on taxiway Hotel. The radar tracks of the two aircraft were parallel with a lateral separation of about 300 feet. The radar data indicated the two aircraft passed one another about 885 feet from the approach end of runway 28R. At the time they passed one another, the helicopter's ground speed was about 58 mph, and the airplane's ground speed was about 50 mph. Additionally, the radar data shows that at the time of the last radar hit from the airplane, the helicopter was more than 1,350 feet from the airplane. BIL operations personnel photographed the scene after the accident. These photographs show a yellow paint transfer on the runway surface, which appears to match the color of the accident airplane, located at 45:48:25.33 north and 108:33:17.42 west, or about 1,616 feet from the threshold of runway 28L and about 18 feet from the runway's right side edge. As determined from the radar data, the transfer mark was located 731 feet beyond the passing point of the two aircraft and about 170 feet beyond the airplane's last radar hit. The airplane's wingspan was 35 feet 2 inches. To produce the paint transfer with its left wing, the airplane's fuselage would have been over the right edge of the runway. The main wreckage was located at 45:48:27.21 north and 108:33:19.17 west, or about 1,808 feet from the threshold of runway 28L and about 111 feet north of the runway's edge. The main landing gear collapsed, the fuselage was twisted, and the engine was displaced aft, damaging the firewall and the instrument panel. Additionally, the bottom of the rudder and the right elevator were bent and wrinkled. The helicopter that was landing on taxiway Hotel was a Eurocopter Deutschland GMBH EC135P1. Its main rotor disc measured 33.46 feet in diameter. The Federal Aviation Administration's Aeronautical Information Manual states that "Pilots of small aircraft should avoid operating within three rotor diameters of any helicopter in a slow hover taxi or stationary hover." In this case, that would be 101 feet for the EC135P1. Additionally, a representative from the helicopter manufacturer's safety department said that a helicopter descending during air taxiing and with a forward speed of about 58 mph, the helicopter's ground speed when it passed the airplane, would produce significantly less downwash relative to what it would produce when static hovering or hover taxiing. At 0826, the reported weather conditions at BIL were: wind 190 degrees at 6 knots; visibility 10 statute miles; cloud condition, clear; temperature 61 degrees Fahrenheit; dew point 55 degrees Fahrenheit; altimeter setting 29.95 inches of mercury. This weather report indicated a direct left crosswind for landing on runway 28L at BIL. Runway 10R/28L is 3,801 feet long and 75 feet wide; it is paralleled on its south side by taxiway H, which is 44 feet wide. Measurements from aerial photographs indicate that the distance from the centerline of the runway and the centerline of the taxiway is 200 feet.
The pilot's inadequate compensation for the wind conditions and failure to maintain lateral and directional control of the airplane during landing.
Source: NTSB Aviation Accident Database
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