SEA08LA069

During a landing on a runway covered by about two to three inches of freshly fallen snow, one of the airplane's main landing gear impacted a snow covered mound of previously plowed snow that had hardened. That impact threw the airplane sideways, whereupon it collided with more of the previously plowed and hardened snow, resulting in the collapse of all the landing gear struts. The investigation determined that the last time that the runway was plowed, the snow had not been cleared all the way to the edge of the runway's paved surface, and there was therefore piles of previously plowed snow on the outer portions of the runway surface. Some of that snow was located 10 to 12 feet inboard of the edge of the runway surface. When the new snow fell, it became very hard to distinguish between the area where the previously cleared surface was covered only by the newly fallen snow, and the area where the chunks of previously plowed snow had piled up, hardened, and then been covered by the new snow. The pilot departed the same airport two days before the accident, and had seen the condition of the partially plowed runway. When he returned for landing on the day of the accident, he assumed that the old snow had been cleared away prior to the new snow falling, and that the entire runway was then covered only with the two to three inches of freshly fallen snow. Because he made that assumption, the pilot did not take advantage of the opportunity to perform a low approach and inspect the entire runway surface prior to landing. Soon after the airplane touched down, the pilot realized that the previously plowed snow was still on the edges of the runway, and that he had not touched down on the centerline. The pilot saw the chunks of snow-covered old snow prior to the impact, but before he could take remedial action, one of the airplane's main gear collided with a chunk of hardened old snow, and the accident sequence was initiated.

On February 4, 2008, about 1130 mountain standard time, a Piper PA-32R-301T, N73BL, collided with hardened chunks of previously plowed snow during the landing roll at Parowan Airport, Parowan, Utah. The airline transport pilot, who was the sole occupant of the airplane, was not injured, but the airplane, which is owned and operated by the pilot, sustained substantial damage. The 14 CFR Part 91 personal transportation flight, which departed Las Vegas, Nevada, about 0900 Pacific standard time, was being operated in visual meteorological conditions. The pilot had originally been on an Instrument Flight Rules (IFR) flight plan, but had canceled his IFR clearance once he had the airport in sight. There was no report of an ELT activation.

According to the pilot, he had landed at the Parowan Airport many times over a number of years, but on the day of the accident the runway was covered with two or three inches of new snow. Because of the snow coverage, he could not easily tell where the centerline of the runway was, and after the airplane touched down, one of its main landing gear impacted a snow covered mound of previously plowed snow. That impact threw the airplane sideways, whereupon it collided with more of the previously plowed snow. During this sequence, all three landing gear struts collapsed, and the underside of the airplane's belly sustained considerable structural damage.

During the investigation it was determined that the last time that the runway was plowed by the Parowan Public Works Department, the snow had not been cleared all the way to the edge of the runway's paved surface. Instead, only about a 50 foot wide swath was cleared on the 75 foot wide surface. Therefore, when the new snow fell, it became very hard to distinguish between the area where the previously cleared surface was covered only by the newly fallen snow, and the area where the chunks of previously plowed snow had piled up, hardened, and then been covered by the new snow.

In a telephone conversation with the NTSB Investigator-In-charge (IIC), the pilot stated that when he departed Parowan two days prior to the accident, there was no snow on the center portion of the runway (approximately a 50 foot wide irregularly cut swath), but that the old previously plowed snow was piled along both sides of the entire length of the runway. He estimated that at that time the piles of old snow extended onto both sides of the runway surface about 10 to 12 feet from its edge. He further stated that fresh snow had fallen while he was gone from the area, and as he lined up for his final approach on the day of the accident, everything appeared white and flat. He therefore assumed that the old snow had been cleared away prior to the new snow falling, and that the entire runway was covered only with the two to three inches of freshly fallen snow.

Because the pilot made that assumption, he did not take advantage of the opportunity to inspect the runway during a low approach prior to landing. Soon after the airplane touched down, the pilot realized that the previously plowed snow was still on the edges of the runway, and that he had not touched down on the centerline. According to the pilot, he saw the chunks of snow covered old snow prior to the impact, but before he could take remedial action, one of the airplane's main gear collided with a chunk of hardened old snow, and the accident sequence was initiated.