Tampa, FL, USA
N184RB
Piper PA-46-500TP
Following a normal touchdown, the right forward support tube on the nose acutuator attach foot failed due to a fatigue crack at the weld joint. The airplane veered to the right causing overstress fracture of the left forward support tube on the nose actuator attach foot, and partial collapse of the nose landing gear. The pilot stopped the airplane on the runway. Service bulletin (SB) 1154A, which was prepared by the airplane manufacturer due to previous failures of the engine mount at the actuator attach foot attach point had been performed 63.9 hours earlier. The SB requires repetitive inspections every 100 hours time in service unless a newly designed engine mount was installed.
"THIS CASE WAS MODIFIED MAY 28, 2008." On January 14, 2007, about 1825 eastern standard time, a Piper PA-46-500TP, N184RB, registered to and operated by Clear Air Aviation LLC, experienced partial collapse of the nose landing gear during the landing roll at Tampa International Airport (KTPA), Tampa, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 Code of Federal Regulations Part 91 personal flight from Boca Raton Airport, Boca Raton, Florida, to KTPA. The airplane was substantially damaged and the private-rated pilot and one passenger were not injured. The flight originated about 1730, from Boca Raton Airport. The pilot stated that prior to touchdown on runway 18L with the wind from the southwest at 3-5 knots, he verified 3 separate times that all landing gears were down and locked. He landed on the runway centerline and when he lowered the nose landing gear to the runway, he initially thought he had a flat tire but the airplane tracked straight. During the landing roll at 25-30 knots, the airplane violently pulled to the right. He applied full braking and stopped the airplane before it traveled off the runway surface. During the last 5 feet of movement, propeller to runway contact occurred. Postaccident examination of the airplane by an FAA airworthiness inspector revealed the nose landing gear was displaced aft approximately 15-20 degrees and the nose wheel was turned to the right 80-90 degrees. The left side of the tire was scratched and gouged; the tire pressure was 55 psi. The bottom wheel well assembly was buckled, and 3, one-inch sections were worn inside the left gear door. The steering arm was broken and the separated piece was not located. Damage to the nose gear strut 60-degree stops were noted. Damage to the engine firewall was noted. Two tubes of the engine mount were separated from the "No Weld - One (1) Piece Foot" at the nose gear actuator attachment area. The engine mount (P/N 102460-002, S/N 217), was retained by NTSB for further examination. Examination of sections of the engine mount by NTSB Materials Laboratory personnel located in Washington, DC revealed both forward support tubes were separated at the weld joint at the left and right nose gear actuator attachment foot location. The weld joint for the left forward support tube exhibited overstress fracture, while the weld joint for the right forward support tube exhibited fatigue cracking. The fatigue cracks and cracks along the opposite edge of the weld bead followed the curves between the overlapping segments of the weld bead. The fatigue cracking was evident over an arc of approximately 60 degrees, and at its deepest penetration, the fatigue crack had propagated through 50 percent of the estimated .08 inch thickness of the weld. The New Piper Aircraft, Inc., prepared Service Bulletin (SB) Nos. 1103B and 1154A, which were applicable to the accident aircraft by make, model, and serial number. Both SB's occurred because of previous occurrences involving cracks on the engine mount in the area of the nose gear actuator attach feet. Service Bulletin No. 1103B, dated November 25, 2003, required repetitive inspections each 100 hours time in service or annual inspection, whichever occurs first, to identify cracks in the specified areas of the engine mount. Service Bulletin No. 1154A, dated July 26, 2006, also required repetitive inspections, every 100 hours time in service, to identify cracks of specified areas of the engine mount. The repetitive inspections in both SB's could be eliminated by installing a new design engine mount. Compliance with Service Bulletins are not mandatory for airplanes operated in accordance with 14 Code of Federal Regulations Part 91. 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 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. The airplane was manufactured in 2001, and was equipped with engine mount P/N 102460-002. The airplane had accumulated 1,066.6 hours since manufacture at the time of the accident. Review of the airplane maintenance records pertaining to Service Bulletin Nos. 1103 (including revisions), and 1154 (including revisions) revealed the following compliance entries. The airplane had accumulated 63.9 hours since SB 1154A was last complied with. Service Bulletin No. Date Complied With Aircraft Total Time 1103 August 6, 2002 176.9 1103A February 28, 2003 230.8 1103A September 17, 2003 267.5 1103B August 2, 2004 323.5 1154A October 25, 2006 1,002.7 Subsequent to this incident, 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 under warranty with engine mount P/N 102460-036 by November 2007; as of March 2007, 107 PA-46-500TP aircraft still 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 inadequate design of the engine mount by the manufacturer, resulting in fatigue failure at the actuator attach foot and partial collapse of the nose landing gear.
Source: NTSB Aviation Accident Database
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