Aspen, CO, USA
N535JR
NEW PIPER AIRCRAFT INC PA-46-500T
The private pilot and passenger were landing following a cross-country flight. As soon as the nosewheel touched down on landing, the airplane pulled to the left. The pilot attempted to correct to the right and the airplane began swerving and exited the right side of the runway and came to a stop in a snow bank. The pilot told investigators the airplane had seven previous instances of the airplane pulling to the left during landing. In each of those cases, the steering departure occurred upon nosewheel touchdown and the pilot was able to regain control. Weather at the time of the accident was clear skies and the winds were variable at five knots. Postaccident examination of the airplane showed the nose gear rake angle was negative (-) .5 to -.7 degrees. Proper rake angle is 0.0 to positive .5 degrees. The manufacturers's analysis of the measured -.5 to -.7 degree rake angle showed that the rake angle maintained a positive margin of safety against dynamic nosewheel shimmy. The investigation could not determine the cause of the steering departure.
HISTORY OF FLIGHT On February 4, 2009, about 1230 mountain standard time, a Piper PA-46-500TP airplane, N535JR, departed the runway during landing at the Aspen-Pitkin County Airport (ASE), Aspen, Colorado. Visual meteorological conditions prevailed at the time of the incident. The airplane received minor damage, and neither the private pilot or passenger were injured. The cross- country flight was being operated as a personal flight under the provisions of 14 Code of Federal Regulations (CFR) Part 91, and an instrument flight rules (IFR) flight plan was filed. The flight originated at Richard Lloyd Jones Airport (RVS), Tulsa, Oklahoma, and was terminating at the time of the incident. The pilot stated that he made a smooth landing on the main wheels and as soon as the nose wheel touched down the airplane began veering left and right uncontrollably. The airplane exited the right side of Runway 15 about 2,000 feet down the runway and came to rest in a snow bank. The pilot also reported this airplane had seven previous events of the airplane pulling to the left during landing. In each of those cases, the steering departure occurred upon nose wheel touchdown and the pilot was able to regain control. There were no reports to the NTSB or FAA for any of the prior events. PERSONNEL INFORMATION The pilot, age 50, held a private pilot certificate with airplane single engine land and instrument ratings. His last flight review occurred on November 3, 2008. His last third class medical evaluation occurred on June 1, 2007. According to the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1), he had 1,600 total flight hours and 500 flight hours in this make and model of airplane at the time of the accident. AIRCRAFT INFORMATION The six-seat, low wing, retractable gear airplane, serial number (S/N) 4697253, was manufactured in 2006. It was powered by a Pratt and Whitney Canada PT6A-42A 500 horsepower engine and equipped with a Hartzell HC-E4N-3Q propeller. A review of the maintenance logbook records showed an annual inspection was completed September 9, 2008, at a recorded 527.8 hours airframe total time and tachometer time. The airplane had accumulated 680 hours total time and tachometer time at the time of the incident. This model airplane is equipped with a retractable tricycle air-oil strut type landing gear which is hydraulically operated by an electric hydraulic pump. A selector handle or switch on the instrument panel to the left of the control quadrant is used to select gear UP or DOWN positions. The nose gear is steerable through a 60 degree arc by use of the rudder pedals. As the gear retract, the steering linkage becomes separated from the gear so that rudder pedal action with the gear retracted is not impeded by the nose gear operation. The nose gear rotates 90° to stow in the horizontal position. A steering bungee is also incorporated in the nose wheel steering mechanism. METEORLOGICAL INFORMATION Weather at ASE at 1153 was reported clear skies, temperature 33 degrees Fahrenheit, altimeter 30.43, and winds calm. The pilot and airport personnel reported variable winds at 5 knots at the time of the accident. AERODROME INFORMATION Runway 15 at ASE is 7,006 feet by 100 feet at an elevation of 7,679.8 feet mean sea level (MSL). It has a grooved asphalt surface and a 2.0 percent up-sloping gradient. TESTS AND RESEARCH The landing gear and nose wheel steering systems were examined for anomalies and proper operation by investigators. With weight on wheels, the nose gear strut extension measured 2.212 inches, the right main landing gear (MLG) strut extension measured 2.75 inches, and the left MLG strut extension measured 2.8125 inches. The nose wheel tire pressure was 70 pounds per square inch (psi). The steering rake angle measured between -.5 degrees and -.7 degrees. The nose wheel strut had .2 degrees of fore/aft movement, which accounted for the differences in the measured rake angle. Piper Aircraft, Inc. PA-46-500TP, Malibu-Meridian Maintenance Manual, Figure 4 (Nose Gear Adjustment), page 4G8, depicted the proper steering rake angle as 0.0 degrees to +0.5 degrees. Nose wheel steering roller clearance was measured with weight-on-wheels and on jacks (weight-off- wheels). With weight-off-wheels, the left and right steering roller clearances both measured greater than .035 inches. With weight-on-wheels, the left and right steering roller clearances both measured .020 inches. The recommended clearance is 0.010 - 0.030 inches with weight on wheels. Rudder cable tension was examined and was found to be appropriately set. The pilot stated at the time of the event landing both passengers weighed 285 pounds, there was 560 pounds of fuel, and 75 pounds of cargo in the rear cargo area. This information was provided to engineers at Piper Aircraft to compute the margin of safety with these conditions and with a nose wheel rake of -.5 to -.7 degrees. According to Piper engineers, “based on this incidents inputs and a 78 knot indicated landing speed (ref. P.O.H. section 5 landing ground roll maximum touchdown speed), shimmy analysis shows a positive margin of safety against dynamic shimmy ( MS = +.14) , even with a negative .70 degree rake angle.” The airplane engine mount, part number 102460-036, S/N 116192, was installed at the Piper Aircraft manufacturing facility and was original manufacturer equipment. Post incident, the engine mount was removed from the airplane and examined at the Piper Aircraft, Inc. manufacturing facility. Prior to removal, there was no evidence of contact between the engine mount and the engine firewall. The nose gear actuator attachment bolt and nut were also intact and turned freely in the actuator mounting hole. The engine mount, which was white in color, was inspected visually and by non-destructive inspection (NDI) methods. No evidence of flexing, cracking, or impact damage was found. The mount was placed in a straightening jig to determine if any bending or misalignment were present. The mount did not show any signs of bending or misalignment. ADDITIONAL INFORMATION Piper Aircraft provided historical information on takeoff and landing excursions of PA-46-500TP airplanes. That data indicated twenty events of runway excursions, in addition to this incident. Six of the events were investigated by the NTSB. Of those six events, four (CHI07IA067, DEN07LA030, MIA07LA038, SEA07IA058) were attributed to deficiencies or failures of the engine mount, one (DEN05LA109) to pilot error, and one (LAX05LA116) to undetermined reasons. The remaining fourteen events were not investigated by the Safety Board since substantial damage and/or serious injuries were not involved. Therefore, limited data was obtained regarding those events. This event was the second recorded runway departure in an airplane equipped with the newest, third generation engine mount (part number 102460-036). The first occurrence occurred on February 27, 2008, with airplane S/N 4697148. This incident resulted in minor damage. The cause of the incident was undetermined. Written Guidance - PIPER AIRCRAFT, INC., PA-46-500TP, MALIBU MERIDIAN MAINTENANCE MANUAL (PA-46 MM), April 15, 2007, contained the following information under the Troubleshooting Nose Gear section: Nose Gear fails to straighten when landing gear extends. - Steering arm roller sheared at top of strut. o Replace defective roller. - Incorrect rigging of nose gear steering. o Check nose gear steering adjustment. On page 4G6 of PA-46 MM, Nose Gear Assembly, Installation, Step B. (5) said “Check the alignment of the nose gear assembly – Alignment, below.” Following the installation checklist were two figures, one labeled “Nose Gear Installation – Figure 3” on page 4G7 and one labeled “Nose Gear Adjustment - Figure 4” on page 4G8. Figure 4 was a diagram of the nose gear assembly. On that diagram “0.0 [degrees] to 0.5 [degrees]” was printed over the nose wheel with arrows pointing to two diverging lines which were drawn vertically over the nose gear strut. Pages 4G9 thru 4G11 contained the written guidance for adjustment and alignment of the nose gear assembly. No guidance was provided regarding methods to measure nose gear rake or to reference Figure 4 during the adjustment or alignment procedures. Page 4G9, Step E. Alignment, (3) stated “With the landing gear in the down locked position, weight proportionally on the nose gear and the nose wheel facing forward, adjust the steering arm by loosening the pivot bolt and moving the adjuster on the bottom of the mount plate until the steering arm clears the rollers by 0.010 - 0.030 in. Make this measurement with the nose wheel locked in alignment with the longitudinal axis and the steering arm parallel to the steering horn pads. Torque the pivot bolt.” On March 27, 2008, Piper issued Customer Information Letter-PA46 Operational and Maintenance Information, Nose Gear Steering (CIL). This letter contained the following information. “Some Piper customers have expressed concerns about the nose gear steering on the PA46 “Malibu” series of aircraft models. This document explains Piper’s response to those concerns and provides specific actions that owners can take to ensure that their aircraft continues to operate properly and conform to factory specifications. When the Meridian was first introduced in 2000, some of these early customers reported an occasional pull to the right at the instant of touchdown. Piper immediately began an extensive testing program in an effort to understand this phenomenon. Although Piper was unable to duplicate the reported condition (either then or since, under varied and extreme conditions), analysis of the test data, combined with research into the dynamic behavior of the steering geometry, has resulted in a two-fold design improvement to the Meridian in 2002 which allows the pilot to better control the steering forces involved: - A higher tire pressure was used to reduce the size of the rolling contact patch, thereby reducing the magnitude of the steering forces. An 8-ply tire inflated to 70 psi replaced a 6-ply tire inflated to 50 psi. - A stiffer bungee was used to increase the pilot’s authority in controlling the steering forces.” The CIL also provided recommended procedures for rigging and maintenance of tire pressure, nose gear rake angle, steering arm / roller gap, and rudder cable tension. The letter provided the following specific procedures for setting rake angle and setting steering arm / roller clearances. “The proper nose gear rake angle for all Malibu models is zero to one-half degree forward from vertical, measured using the airframe lower skin just aft of the nose gear doors as a horizontal datum with the aircraft on jacks. In other words, the relative angle between the lower (belly) skin and the nose gear strut should range from 90.0 degrees to 90.5 degrees. See figure 1. A rake angle outside of this range may result in dynamic instability, creating steering forces that exceed the pilot’s ability to control. This angle is set by adjusting thread engagement in the nose gear actuator‘s rod end bearing as described in the maintenance manual. The nose gear rake angle is properly adjusted and verified at the factory and should be inspected and/or adjusted by an FAA-licensed mechanic according to the schedule and instructions in the maintenance manual, any time the pilot experiences poor steering, or there is replacement or service to the nose gear trunnion, the nose gear actuator, or the engine mount.” “Mounted on top of the nose gear trunnion are two nylon rollers which are used to translate the rotation of the steering arm (from rudder pedal movements) into rotation of the nose wheel. When the gear is in the down and locked position, the two nylon rollers are directly forward of the steering arm as shown in figure 1. Excessive clearance between these two rollers and the steering arm will result in loose steering and allow the nose wheel to point in a different direction than is commanded by rudder pedal inputs. The correct clearance between the Steering Arm and the Rollers is adjusted and verified at the factory to be 0.010 to 0.030 inches with aircraft weight on wheels. This clearance should be inspected and/or adjusted by an FAA-licensed mechanic according to the schedule and instructions in the maintenance manual or any time the pilot experiences poor steering, or there is replacement or service to the nose gear trunnion, the nose gear actuator or the engine mount.” Figure 1 provided a schematic drawing of the nose gear system. The drawing depicted the proper configuration of the nose gear steering arm / rollers and the proper method of determining the rake angle. It showed the proper rake angle being 90 degrees (+0.5 degrees to 0.0 degrees) measured from the centerline of the nose gear strut to the aircraft skin behind the nose gear. A review of the airplane maintenance log revealed the airplane nose gear system had been worked on for various reasons eight times since the airplane was purchased. The work had been performed by Sun Aviation, Inc. seven of the eight times. Five of the seven work orders resulted in adjustment of the nose gear steering roller gap and one involved adjustment of the steering roller gap and the nose gear rake angle. The NTSB investigator interviewed the Sun Aviation technician who performed the last work on the airplane’s nose gear system. During the interview he stated he was unaware of the CIL. When asked how he set the proper steering roller arm clearance he demonstrated on a PA-46 that he set a .020 inch gap between one roller and the steering arm while the second roller was touching the steering arm. When asked how he knew what the proper rake angle was and how he set it, he referred to Figure 4, page 4G8 of PA-46 MM for the proper angle. He then demonstrated a technique for determining the rake angle on the airplane by measuring 38.75 inches from the back edge of the nose wheel steering support plate to the lower, aft edge of the nose gear trunnion. Piper Aircraft personnel set the angle distance of 38.75 inches on a PA-46-500TP airplane on the production assembly line, as was demonstrated by the Sun Aviation technician. They then measured the nose gear rake angle using the procedures outlined in the CIL. Using the CIL prescribed method of measuring the rake angle the actual rake angle set by using the 38.75 inch measurement technique was negative .4 degrees.
The pilot's inability to maintain directional control of the airplane during landing for undetermined reasons.
Source: NTSB Aviation Accident Database
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