NTSB Factual Report

HISTORY OF FLIGHT

On May 9, 2014, about 1400 eastern daylight time, a Pacific Aerospace Corp 750XL, N750SS, experienced a left main landing gear separation following a hard landing and subsequent go-around at Warrenton Air Park (7VG0), Warrenton, Virginia. The pilot subsequently performed a precautionary landing at the airport and the airplane sustained substantial damage to the left wing. The commercial pilot and one passenger were not injured. The airplane was registered to Maxim Aviation LLC and was operated by DC Skydiving under the provisions of Title 14 Code of Federal Regulations Part 91 as a skydiving flight. Visual meteorological conditions prevailed and no flight plan was filed for the local flight that departed about 1330.

According to the pilot, the airplane had 70 gallons of fuel on board prior to departure with the skydivers. While on final approach to runway 22, about 15 feet above ground level, the airplane "broke from straight and level flight," the left main landing gear contacted the turf runway, and he immediately performed a go-around. Personnel on the ground contacted the pilot via radio and informed him that the left main landing gear had detached from the airplane. He elected to perform a precautionary landing on runway 4. Once the landing was assured, he initiated an emergency shutdown procedure for the engine and landed on the right main landing gear, subsequently the left wing settled to the ground, and the airplane slid off the side of the runway.

According to the passenger, after the skydivers exited the airplane they began their descent to land. While on final approach, the airplane appeared to be above the approach path. The pilot performed a go-around maneuver and subsequent tear-drop entry to land the opposite direction on the runway. During the final approach, after clearing the edge of the tree line, the airplane descended toward the runway and the pilot pulled back on the stick to level the airplane. The passenger reported no change in pitch attitude. The airplane contacted the turf runway, bounced, and the pilot performed an aborted landing. The pilot attempted a third landing attempt. Upon touchdown the pilot pulled the stick back and pushed on the rudder in order to minimize the speed in which the left wing would make contact. The pilot kept the airplane straight on the runway until the left wing made contact and subsequently the airplane came to a stop.

PERSONNEL INFORMATION

The pilot, age 39, held a commercial pilot certificate with ratings for airplane single and multiengine land, and instrument airplane which was issued on January 13, 2008, and a second-class airman medical certificate issued April 16, 2014, with no limitation. The pilot reported 1,405 total hours of flight experience, and of those, 50 hours were in the accident aircraft make and model.

AIRCRAFT INFORMATION

The low-wing, fixed-gear, all metal monoplane design was manufactured in 2005. It was powered by a Pratt & Whitney Canada PT6A-34, 750-hp turboprop engine and equipped with a MT-Propeller model MTV 16-1-E-C-F-R(P) controllable pitch propeller. A review of copies of maintenance logbook records revealed a progressive inspection was completed on December 12, 2013, at a recorded tachometer reading of 3,576.0 hours and an airframe total time of 3,914.4 hours.

According to a maintenance entry dated March 9, 2012, at an airframe total time of 3,199.8 hours, all of the airplane's landing gear were removed. The entry further listed that the left main landing gear was replaced with a "heavy left" that would accommodate "large tires." The entry further stated that all gear attach bolts were torqued after the paint was stripped from the clamp area to minimize fastener "untorqueing."

The aircraft was designed for a variety of utility roles, including freight, agricultural application, passenger operations, and parachuting operations. The accident airplane was being utilized, at the time of the accident, in parachuting, or skydiving, operations.

METEOROLOGICAL INFORMATION

The 1335 recorded weather observation at Warrenton-Fauquier Airport (HWY), Warrenton, Virginia, located 5 miles to the southwest of the accident location, included calm wind, visibility 10 miles, clear skies, temperature 27 degrees C, dew point 22 degrees C, and barometric altimeter 30.05 inches of mercury.

AIRPORT INFORMATION

The airport was a privately owned airport and at the time of the accident and did not have an Federal Aviation Administration (FAA) operating control tower. The airport was equipped with two turf runways designated as runway 4/22, and 15/33 and both were listed "in good condition." Runway 4/22 was 2,215-foot-long by 70-foot-wide, and runway 15/33 was 2,000-foot-long by 70-foot-wide. The airport was surveyed at 442 feet above mean sea level.

WRECKAGE AND IMPACT INFORMATION

The airplane was removed from the runway and examined by an FAA inspector. Substantial damage was noted to the left main landing gear attachment point and left wing spar. Examination inside the left wing fuel tank revealed several pieces of a white polymeric-like material and a small amount of a gel-like substance loose within the fuel tanks. According to the pilot, 70 gallons of fuel were removed, following the accident, from the left wing tanks; however, the pilot did not report if any fuel was removed from the right wing tanks.

TESTS AND RESEARCH

The left main landing gear attach bolts and lower clamp were sent to the NTSB Materials Laboratory for examination. The bolts were 3/8 inch diameter bolts. Three of the bolts were fractured through the shank and a portion of the lower clamp's aft bolt remained trapped within the clamp. The fourth bolt, which was the lower clamp forward bolt, was cut to facilitate removal of the hardware from the airplane. The lower cylinder clamp consisted of a two-piece cast clamp, with an inboard and outboard component. The "as received" clamp consisted of three pieces, the outboard component was intact, but deformed, and the inboard component was fractured between the forward and aft bolts. The forward bolt hole on the lower clamp was elongated at the split line, which was consistent with the presence of the bolt during the spreading deformation. The nuts, as received, on both upper bolts and the lower forward bolt were threaded fully onto the respective bolts, exposing about six bolt threads. However, a photograph taken of the upper bolts by an FAA inspector, who responded to the accident location, showed that the upper bolts, prior to removal from the landing gear, had about three full bolt threads exposed. An aft outboard bending moment was noted on a landing gear clamp piece. Fretting marks were also noted and was indicative of the clamp movement relative to the bulkhead; however, the time of the fretting could not be conclusively determined. Examination of the three fractured bolts revealed fracture and deformation patterns consistent with shearing overstress.

Pieces of the white polymeric material and a gel-like red substance found in the fuel tank were sent to the NTSB Materials Laboratory for examination. The white polymeric material was consistent with polyurethane based material that was used to coat the fuel tank. The gel-like red substance was consistent with a silicone sealant. The white polymeric material pieces were examined to determine the fracture mechanism. The fracture surface exhibited chevron lines which were consistent with ductile (overstress) tearing failure of the material. The fracture surfaces also contained entrapped gas voids within the material which was consistent with air becoming trapped in the sealant prior to curing.

NTSB Probable Cause

The pilot’s improper landing flare, which resulted in a hard landing and separation of the left main landing gear.