Piper PA-46-600TP N627PR

The pilot was landing the airplane with a right quartering headwind, resulting in a right crosswind component of about 10 to 14 kts, which was less than but near the airplane’s maximum demonstrated crosswind component of 17kts. The airplane touched down left of runway centerline. After touchdown, the pilot attempted to correct to the right toward the centerline with rudder inputs. As the airplane decelerated through about 68 kts and approached the runway centerline, the airplane entered a hard right turn about a 45° angle, and the pilot reported that he was unable to control the turn with left rudder input. The airplane departed the right side of the runway, about 1,330 ft from the threshold and about 570 ft after touchdown, and the nose landing gear (NLG) collapsed. The airplane sustained substantial damage to the engine mount. Postaccident examination of the runway surface revealed rubber transfer markings consistent with the NLG, right main landing gear (RMLG), and left main landing gear (LMLG). The NLG transfer mark began about 900 ft from the threshold and about 10 ft left of the centerline, with light intensity and its tread pattern evident, consistent with a rolling, non-skidding tire. The rolling tire marking continued until the right veering began, at which point it was of moderate intensity with tread pattern evident and transitioned to heavy intensity and no tread pattern, consistent with a skidding tire. A review of the airplane’s avionics data revealed that the RMLG touched down first, followed by the LMLG about 1 second later, consistent with a right crosswind landing. The NLG touched down about 1 to 2 seconds after the RMLG. Starting about 2 seconds after LMLG touchdown, the heading and track diverged, with the nose to the right of the track, until near the runway departure location, indicating that the airplane was in a skid. The maximum divergence occurred about 1 second before the runway excursion, when the heading was about 223° and the track was about 195°. At the same time, the lateral acceleration increased, also consistent with the airplane being in a left skid. The airplane departed the runway with the heading and track mostly aligned. Postaccident examination of the NLG assembly did not reveal anomalies that would have affected its operation or steering. The rake angle of the NLG is designed to be 90° from the airplane longitudinal axis with a very tight tolerance, allowing 0.5° forward rake and zero aft rake. The zero-rake angle is good for static stability and taxiing at slower speeds but can be problematic for dynamic stability at higher speeds. A zero or aft rake can tend to cause the NLG tire to turn more sharply if deflected in some conditions. On NLG touchdown, the NLG strut will deflect aft due to spin-up loads, increasing the negative rake that could cause instability, and will undergo a damped oscillation. The design of the NLG with zero rake and no trail requires that the NLG tire be aligned with the runway upon touchdown, which it was during the accident landing as evidence by the runway markings. Any misalignment or steering input may result in a steering hardover due to the dynamic instability inherent in the NLG design. The circumstances of this accident indicated that the NLG turned hard right soon after touchdown, when the NLG dynamic instability manifested itself as the pilot was correcting back to the centerline of the runway with rudder input. The manufacturer redesigned the lower NLG fork area to move the axle 0.5 inches aft of the steering axis. This is equivalent to raking the NLG forward 5°, making it inherently dynamically stable. The new NLG should be dynamically stable even during aft deflection since the steering axis will remain forward of the vertical axis (center of the tire contact patch) and provide a restoring force to the NLG tire if deflected. The new NLG improves the dynamic stability of the NLG allowing the nose wheel to self-center.

Quoted verbatim from the NTSB record.