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On November 30, 2006, at 0850 mountain standard time, a Piper PA-46-500TP, single-engine turboprop airplane, N804JH, sustained substantial damage when it impacted terrain following a loss of directional control during takeoff roll from the Steamboat Springs Airport/Bob Adams Field (SBS), Steamboat Springs, Colorado. The commercial pilot, who was the sole occupant, was not injured. The airplane was registered to Twin Landfill Corporation, Bozeman, Montana, and operated by the pilot. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed for the Title 14 Code of Federal Regulations Part 91 personal flight. The flight was originating at the time of the accident and was destined for Canon City, Colorado.
According to the pilot, during the taxi to runway 32, he noted the runway surface contained some icy and snow packed areas; however, the majority of the runway surface was exposed. The pilot stated that the partially snow covered runway was not a concern because he conducted operations with those conditions several times in the past. The pilot applied power to the engine and the takeoff roll was smooth. The pilot noted that the runway centerline was somewhat obscured by snow and the airplane drifted slightly to the right of centerline. Approximately 50 to 60 knots (1/3 of the way down the runway), the airplane "suddenly turned hard to the left and started to skid." The pilot immediately reduced power to idle and did not apply brakes or reverse. Subsequently, the airplane departed the left side of the runway. The airplane continued for approximately 300 feet in the snow-covered terrain before it came to rest. During the excursion, the nose gear collapsed and the propeller struck the terrain. The pilot reported the winds "a little above calm" at the time of the accident.
The pilot, who was seated in the left front seat during the accident flight, held a commercial pilot certificate, with single-engine, multi-engine, and instrument airplane ratings. The pilot was issued a second-class medical certificate on December 28, 2005, with a limitation for corrective lenses. According to the Pilot/Operator Aircraft Accident/Incident Report (NTSB Form 6120.1), the pilot reported he had accumulated a total of 3,160 flight hours, of which 207 hours were accumulated in the same make and model as the accident airplane. The pilot's most recent flight review was accomplished on September 6, 2006, in the accident airplane.
In the three months preceding the accident, the pilot had accumulated 55 hours in the accident airplane, of which 18 hours were dual instruction.
The turboprop airplane, serial number 4697044, was manufactured in 2001 and issued a normal airworthiness certificate. At the time of the accident, the airplane had accumulated a total of 595 hours since new. The pilot purchased the airplane in January 2005.
The PA-46-500TP airplane is equipped with retractable tricycle air-oil strut type landing gear, which is hydraulically operated by an electric hydraulic pump. The landing gears swing to the down position and each actuator extends to its locked position, a switch located on each actuator activates to indicate by a green light that the gear is safely down and locked. Each landing gear is retracted and extended by a single hydraulic locking cylinder attached to the oleo strut housing. The gears are held in their up position by hydraulic pressure on the cylinder.
The nose gear is steerable through a 60-degree arc by use of the rudder pedals. Movement of the pedals is transmitted to the steering arm by two steering pushrods, a steering bellcrank and a steering bungee. As the gear retracts, 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 degree (left) to stow in the horizontal position.
The nose landing gear assembly (trunnion) attaches to the two forward lower attachment points on the engine mount. The nose gear downlock actuator attaches to the rear of the engine mount. The upper actuator fitting is secured in the rear engine mount attach feet with an AN 7-17 bolt, two washers and a locking nut.
On January 28, 2002, Piper issued Service Bulletin (SB) 1106, Nose Gear Steering System Improvement, which contained the following information. Purpose: There have been field reports of turning tendency immediately following nose wheel touch down during landings primarily, when cross wind conditions are present and/or when applying full propeller reverse. A contributing cause of the turning tendency has been identified as reduced nose gear steering authority, which under certain conditions, can allow the nose gear steering rotation to momentarily exceed the pilot's input. This Service Bulletin recommends mandatory incorporation of nose gear installation modifications that increase the pilot's steering authority. Failure to incorporate these modifications may increase the possibility of a turning tendency during landing. Compliance Time: To coincide with next regularly scheduled maintenance event, but not to exceed the next 100 hours time in service.
A review of the maintenance records revealed that SB 1106 was incorporated and installed on the accident airplane.
On November 25, 2003, Piper issued SB 1103B, Engine Mount Inspection, which contained the following information. Purpose: It has been determined that cracks may develop on the engine mount in the area of the nose gear actuator feet. This condition typically occurs when the nose landing gear is subjected to excessive loads, possibly through hard landings, rough field operations, excessive speed turns and/or improper towing of the aircraft. PART I of this SB requires a repetitive inspection of the engine mount. PART II of this SB requires replacement of the engine mount. Compliance Time: PART I Inspection to coincide with the next regularly scheduled maintenance event, and each 100 hours time in service or annual inspection, whichever occurs first, thereafter or until PART II of this SB is accomplished. PART II Replacement if cracks are found during the inspection in PART I, replace cracked engine mount. Note: Compliance with PART II of this SB will relieve the repetitive inspection requirements of PART I of this SB. PART II: Insure the new engine mount (P/N 102460-002) has the one piece feet. The old engine mount has a two piece welded foot. This welded area is where the cracks in the engine mounts have been found.
A review of the maintenance records revealed that SB 1103B Part I was completed on January 24, 2005, at a total airframe time of 433.0 hours. The records indicated the original engine mount was installed on the airplane.
During a January 2006 incident, the airplane sustained minor damage to the nose landing gear. According to the maintenance logbook entry for the repairs and information provided by the pilot, the engine mount was removed and shipped to Kosola & Associates, Inc., Albany, Georgia, for repairs (the type of repairs required were not specified in the records). During that time, the Kosola facility experienced a fire and the airplane's engine mount was destroyed.
While the airplane was undergoing repairs for the January 2006 incident, Piper issued SB 1154A, Engine Mount Inspection, on July 26, 2006, which contained the following information. Purpose: It has been determined that cracks may develop on the engine mount in the area of the nose gear actuator feet. This condition typically occurs when the nose landing gear is subjected to excessive loads, possibly through hard landings, rough field operations, excessive speed turns and/or improper towing of the aircraft. PART I of this SB requires the a repetitive inspection of the engine mount. PART II - REPLACEMENT: If cracks are found during the Inspection in PART I, replace cracked engine mount with (P/N) 102460-036 Engine Mount Assembly. Repetitive inspection is no longer required if the engine mount is replaced. Compliance Time: To coincide with the next regularly scheduled maintenance event but not to exceed 100 hours. Thereafter, at 100 hour intervals. Note: New Piper has developed corrective action to eliminate this on-going inspection requirement. A new mount with improved service life has been developed; P/N 102460-036. The original mount 102460-002 will no longer be available as a service part replacement. If the original mount 102460-002 is replaced with the new mount, compliance with PART II of this Service Bulletin will relieve the repetitive inspection requirements of Part I of this Service Bulletin.
The pilot elected to have Kosola replace the mount with a modified engine mount assembly, (Kosola P/N 102460-02, S/N 965623). The engine mount was modified per a Kosola & Associates, Inc., supplemental type certificate (STC) SA02779AT. According to Kosola, the STC redesigns and reinforces the original engine mount in the attachment areas addressed in Piper SB 1103B. The pilot indicated that he elected to have the STC'd mount installed due to the following reasons: 1. Piper lead time to obtain a new redesigned mount (P/N 102460-036; reference Piper SB 1154A) was over two months. 2. The new Piper redesigned mount was more expensive than the STC Kosola mount. 3. The Kosola mount eliminated the recurrent inspection as required in Piper SB 1103B and 1154A. The repairs to the airplane from the January incident were completed on August 31, 2006, at a total airframe time of 540.2 hours.
The Steamboat Springs Airport (SBS) is a public, non-towered airport located approximately 3 miles northwest of Steamboat Springs, Colorado, at a surveyed elevation of 6,878 feet. The airport features one runway, Runway 14/32, which is 4,452 feet long and 100 feet wide. The runway surface material is asphalt and grooved.
WRECKAGE AND IMPACT INFORMATION
The NTSB investigator-in-charge (IIC) and representatives from Piper examined the airplane after it was recovered and located on a ramp at SBS. Examination of the airplane revealed the engine mount and nose gear downlock actuator bushings were bent upwards and aft. The nose gear was collapsed and located in the nose gear wheel well. The nose gear downlock actuator piston was separated from the engine mount attach feet and located past the firewall into the engine area. The AN 7-17 bolt and associated hardware (washers and nut), which secured the actuator to the mount, were not located at the time of this examination.
The nose gear assembly was extended, and the nose landing gear steering system was examined. Continuity was established between the nose gear assembly, steering horn, and rudder pedals. The nose gear tire and strut were free to rotate to the left and right control stops. The nose gear tire was a 8-ply and the tire air pressure was measured at 45 pounds per square inch (psi). The steering arm adjustment screw was found within specifications relative to the nose gear steering horn. The nose gear steering bell crank stop screws were adjusted within limits. Examination of the steering system revealed no anomalies with the rigging, adjustment and alignment.
The left wing tip was crushed aft approximately 2 feet inboard of the wing tip. The left wing was pushed aft and separated from the forward wing glove attachment. The upper and lower left wing skin, aft of the main spar, were buckled and deformed. The left and right main landing gears were in the extended position.
Examination of the runway surface revealed three skids marks. A single skid mark, consistent with the nose landing gear tire, began on the runway centerline and continued approximately 6 feet to the right of runway centerline. The skid mark then began an arc to the left and continued off the runway surface. Two other skid marks, consistent with the left and right main landing gear tires, began to the right of centerline and continued in an arc to the left until departure from the runway surface. The distance between the nose and left main gear skid marks was 39 inches, and the distance between the nose and right main gear skid marks was 100 inches. These measurements were recorded at the edge of the runway surface.
During the time of the accident, snow-covered terrain lined the side of the runway. Due to runway snow removal operations, a snow bank, approximately 2 feet high, was located approximately 10 feet off the side of the runway.
TEST AND RESEARCH
On February 6, 2007, at the facilities of Beegles Aircraft Services, Greeley, Colorado, the NTSB IIC and a representative from Piper removed the engine and engine mount from the accident airplane. Examination of the engine mount revealed the mount was bent near the nose gear actuator attach feet. The AN 7-17 actuator attach bolt was found fractured into two halves. Each half of the bolt was found in the engine cowling area, and one bolt half contained the self locking nut. The fractured bolt was retained for further examination by the NTSB Materials Laboratory, and the engine mount was retained for further examination.
According to the NTSB Materials Laboratory factual report, the actuator attach bolt was fractured through the grip area about 0.86 inches from the underside of the hex head. An equal length of the bolt was contained in the self locking nut. The chamfered end of the bolt extended slightly past the nut, but no bolt threads were visible. Examinations of the fracture revealed smooth matte gray fracture faces with adjacent deformation of the bolt typical of a shearing overstress separation. No indications of preexisting cracking or corrosion were uncovered. Hardness measurements both on the grip and hex head flats of the bolt were consistent and averaged 27.1 HRC (Rockwell Hardness C Scale). Utilizing a Wilson Chart 60, this hardness level indicated an approximate tensile strength of 128,000 psi.
On March 21, 2007, the NTSB IIC, a NTSB Structural Engineer, a FAA Structural Engineer, and Piper engineers examined the engine mount at the Piper Aircraft, Inc., facilities in Vero Beach, Florida. In addition to the accident mount, 4 mounts from other accident and incidents were examined (Ref: NTSB Accident/Incident Reports - SEA07IA058, MIA07LA038, CHI07IA067, and LAX05LA116). Three mounts, including this accident mount, were bent near the nose gear actuator attach feet, and no cracks were noted. The two other mounts displayed fractures at the nose gear actuator attach feet. The two fractured mounts were retained for further examination by the NTSB Materials Laboratory.
According to NTSB Accident Report, LAX05LA116, a review of the FAA database revealed there have been 32 PA-46 aircraft that have veered off the 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. Since the LAX05LA116 report, 4 Piper PA-46-500TP aircraft (including this aircraft) have experienced a nose landing gear failure and/or loss of directional control.
According to Piper, due to the recurring cracked engine mounts, the original engine mount was redesigned. Piper stated, "The redesign for the engine mount started with the determination, from customers in the field, that cracks were developing on the engine mount in the area of the nose gear attachment feet and in the areas immediately outboard of the nose gear pivot points. Piper reviewed several broken engine mounts and determined a stronger mount was necessary. Working with the FAA and with their approval, Piper redesigned the mount and have not experienced any failure with the new design." The redesign process included finite element model analysis and various testing programs. Piper stated, "The steps taken by Piper were additional testing and analysis beyond the minimum required FAA levels were performed, to insure that the new design would have a higher level of durability and safety." The original mount design had not incorporated these types of design tools. Post-event engineering examination of the original engine mount and STC'd engine mount revealed that there was compliance (flexibility) in the engine mount actuator attach feet structure, sometimes resulting in the cracking of the engine mount at the actuator feet. This compliance issue was sometimes exasperated at various speeds, resulting in a high speed shimmy effect and subsequent uncommanded left or right turn of the nose wheel during takeoff and/or landing.
On March 28, 2007, Piper issued SB 1154B, Engine Mount Inspection. According to the SB details, SB 1154B supersedes SB 1154A and SB 1154. SB 1154B shortens the repetitive inspection requirement for the engine mount from 100 hours to 50 hours. The SB states that Piper has developed corrective action to eliminate the on-going inspection of the mount. A new mount with improved service life has been developed; P/N 102460-036. The original mount will no longer be available as a service part replacement. If the original mount 102460-002 is replaced with the new mount, the repetitive inspection will no longer be applicable.
The new engine mount, P/N 102460-036, incorporates a one piece design at the actuator attach point, eliminating the two piece feet design. The one piece design provides a less compliant structure, which prevents relative motion between the two feet in the original engine mount design.
According to Piper personnel, all original mounts will be removed and replaced with engine mount P/N 102460-036 by November 2007; as of March 2007, 107 PA-46-500TP aircraft needed the engine mount replaced. Piper stated that all PA-46-500TP customers have been contacted regarding the replacement of the mount and a replacement schedule has been developed. The NTSB has requested that Piper update the NTSB regarding the status of the mount replacement.
The airplane was released to the owner's representative.