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On March 15, 2005, at 1410 mountain standard time, a Piper PA-46-500TP (Meridian), N504SR, veered to the left and the nose gear collapsed while landing on runway 3 at the Flagstaff Pulliam Airport (FLG), Flagstaff, Arizona. The private pilot and passenger were not injured. The airplane sustained substantial damage. The airplane was registered to Synergy Aviation LLC, Missoula, Montana, and the pilot was operating it as a personal flight under the provisions of 14 CFR Part 91. Visual meteorological conditions prevailed, and an instrument flight rules flight plan had been filed. The cross-country flight originated from Heber, Utah, at 1245, and was destined for Flagstaff.
According to the pilot's written statement, he received weather information for Flagstaff while en route, and was also informed by air traffic control that the winds were from 020 degrees at 12 knots with gusts to 16 knots. He established the airplane in a normal traffic pattern for runway 3. On downwind, the pilot selected 10 degrees of flaps and the landing gear were down and locked. As the pilot maneuvered the airplane onto the base leg, he selected 20 degrees of flaps at 100 knots. On final approach the airplane was established at 90 knots with full flaps extended. The pilot reported that the winds were almost right down the runway and there was little, if any, crosswind component.
The pilot reported that his main landing gear touched down normally, but as soon as the nose landing gear touched down, the aircraft "immediately pulled left without normal rudder control." He added that, "it was if the nose gear was not responding to normal input." The airplane veered off the left side of the runway where the nose landing gear collapsed after impacting an 18-inch snow bank. The right wing contacted the ground and the airplane came to rest upright. The pilot contacted the tower and announced what had happened, retracted the flaps, pulled the emergency fuel shutoff lever, shutoff electrical systems, and exited the airplane.
A witness, who worked for the local fixed base operator, stated he observed the entire approach and everything appeared normal. The aircraft touched down initially just after taxiway A7 on runway 3 (A7 is approximately 1,000 feet down the 6,999-foot runway). Immediately after touchdown, the aircraft looked like it lifted back up then set back down. The right wing was much higher than the left. The airplane then turned almost 90 degrees to the left with the propeller facing the taxiway and continued down the runway. The aircraft skidded into the infield where it looked as if the nose gear collapsed. The witness believed the propeller and right wing hit the ground and thought the airplane was going to flip over onto its back because the tail was almost vertical.
The outboard 1.5 feet of the right wing was bent up and the leading edge displayed damage. According to The New Piper Aircraft personnel, the damage to the wing tip, which is considered a structural element, was substantial.
At 1456, the weather observation facility at FLG reported the wind from 040 degrees at 11 knots with gusts to 17 knots. At 1522, the wind was reported from 050 degrees at 15 knots.
The airport operations manager stated that tire skid marks were visible on the runway leading up to the airplane. The tire skid marks originated near the runway centerline, but then veered to the left approximately 75 degrees from the runway centerline. The right wing tip scraped the ground when the airplane veered to the left.
Review of photographs taken by the airport operations manager revealed two heavy tire skid marks associated with the main landing gear tires veering to the left side of the runway as the manager explained. A skid mark associated with the nose landing gear tire does not appear until the main landing gear skid marks were between the runway centerline and the left side runway edge line. In addition, at the initial point of marking, the nose tire skid mark was about 1.5 feet outside (to the left of) the left main landing gear tire skid mark. As the skid marks neared the runway edge line, the nose tire skid mark crossed over the left tire skid mark, but remained within 1.5 feet to the right of the left tire skid mark.
According to the Federal Aviation Administration (FAA) inspector who responded to the accident site, the bolt that secured the nose landing gear actuator to the engine mount was sheared, and the nose landing gear steering arm was broken. The nose tire displayed scratches and gouges around its circumference that were oriented at 90-degree angles to the direction of rotation.
The turboprop airplane (serial number 4697165) was manufactured in 2003 and issued a normal airworthiness certificate. At the time of the accident, the airplane accumulated a total of 186.9 hours since new. The only maintenance conducted on the nose landing gear system was a replaced nose gear door hinge, which took place on May 6, 2004, at an aircraft total time of 102.4 hours, and after 64 landings. On May 19, 2004, the tires were "serviced" at an aircraft total time of 104.20 hours.
TESTS AND REASEARCH
On March 18, 2005, an investigator from The New Piper Aircraft examined the nose landing gear and airframe. According to the investigator, he was provided with the sheared bolt that secured the nose landing gear actuator to the engine mount. The head of the bolt was not recovered. The threaded section of the bolt with the nut still in place was recovered. Visual examination of the bolt fracture surface appeared smeared and deformed as if it had undergone a sheer load failure. The air pressure of the nose tire was checked. The outside air temperature at the time was 37.1 degrees Fahrenheit, and the tire pressure gauge indicated about 72 pounds per square inch. The nose wheel tire exhibited scuffmarks across the treads starting from the right side of the tire going to the left side.
The scuffmarks appeared consistent with the tire sliding across the pavement sideways. The left main tire appeared to be in good condition and no flat spots were observed. The right main tire appeared to be slightly worn, especially on the outboard side, but no flat spots were observed.
The National Transportation Safety Board investigator-in-charge (IIC) examined the airplane at FLG on May 8, 2005. The Safety Board IIC noted that the steering arm was broken to the left of the steering arm attachment bolt, in an area corresponding to the inboard edge of the riding face for the left roller bushing (or adjacent to the steering horn's pads). No additional anomalies were noted with the steering mechanism. The IIC submitted the steering arm and steering bungee to the Safety Board Materials Laboratory in Washington, D.C.
The Safety Board Materials Laboratory examined the steering arm and bungee. Both fracture faces of the broken steering arm displayed coarsely textured and reflective characteristics, which is typical of an overstress fracture in a cast metal component. Optical emission spectroscopy (OES) was performed on a cross section of the steering arm. Its composition was consistent with the aluminum alloy that the manufacturer specified for the component.
The steering bungee spring constant was compared to that specified by the manufacturer. The specified spring constant equated to approximately 156 pound-force (lbf) per inch, and the calculated spring constant determined by lab tests equated to 137 lbf/inch.
The bolt that secures the landing gear actuator to the engine mount was an AN 6-32A.
According to the FAA inspector, review of their database revealed there have been 32 PA-46 aircraft that have veered off the side of the runway; all but 4 veered off the left side of the runway. The majority of the runway excursions occurred in the 310 and 350 series of the PA-46 and not the 500 series. There were two previous 500 series of the PA-46 that veered off the side of the runway, one to the left and the other to the right. The Safety Board investigated the one that veered to the right side of the runway since the airplane sustained substantial damage (see NTSB accident report number FTW01FA107). It should be noted that the majority of the 32 events mentioned above have not been investigated by the Safety Board since substantial damage and/or serious injuries were not involved. Therefore, limited data was obtained regarding the events.
Review of NTSB accident report number FTW01FA107 revealed the PA46-500TP touched down and began to veer to the right. The airplane continued off the right side of the runway. As the airplane headed toward hangars and bystanders, the pilot elected to abort the landing and applied full power. The airplane turned back toward the runway eventually impacting an embankment and a runway end identifier light before coming to a stop. The post accident examination of the nose landing gear revealed the support structure (tubing) was separated from the hydraulic actuator. Metallurgical examination of the structure revealed no preexisting anomalies leading to their failure. The fractures were all consistent with tensile bending overstress separations.
During the course of that investigation, The New Piper Aircraft's engineering department conducted numerous taxi and flight tests in an attempt to duplicate what the pilot reported. The tests consisted of normal and crosswind takeoffs and landings, high-speed taxi testing, and landing and taxi tests using "abnormal, abusive nose steering techniques." No anomalies were noted, and the pull to the right experienced by the accident airplane was not duplicated.
According to The New Piper Aircraft, there have been reports of "temporary loss of directional control immediately following nose wheel touch down during landings, primarily when crosswind conditions are present and/or when applying full propeller reverse. A contributing cause of the directional control problems has been identified as insufficient nose gear steering authority, which under certain conditions, can allow the nose gear steering rotation to momentarily exceed the pilot's input." Therefore, on January 28, 2002, The New Piper Aircraft issued Service Bulletin No. 1106, which recommended the incorporation of nose gear installation modifications. The modifications were intended to increase the pilot's steering authority.
According to The New Piper Aircraft, since that service bulletin was issued in January 2002, and the accident airplane was manufactured in 2003, all of the nose gear modifications were utilized in the accident airplane.