SEA07IA058

At the end of the landing rollout the pilot experienced a loss of control, which resulted in the airplane veering off the left side of the runway and impacting a snow bank before the nose landing gear collapsed. An examination of the nose gear revealed that the rear actuator bolt had failed due to overload during the event sequence and that the engine mount was bent near the nose gear actuator attach feet. Following the identification of a number of cracked engine mounts, several Piper service bulletins were issued and the original engine mount was redesigned. The redesign process included finite element model analysis and other testing programs. These design tools were not incorporated in the original mount design. During a postaccident examination of a similar accident in Steamboat Springs, Colorado, in 2006, investigators found that there was compliance (flexibility) in the original engine mount actuator attach feet structure, which sometimes resulted in cracks in the engine mount at the actuator feet. The NTSB’s investigation of the Steamboat Springs accident determined that compliance was sometimes exacerbated at some speeds, resulting in a high shimmying effect and a subsequent uncommanded left or right turn of the nosewheel during takeoff or landing. Subsequent to the Steamboat Springs investigation, evidence was received of bulkhead damage immediately behind the engine mount found on a PA-46-310P in Greeley, Colorado. The Steamboat Springs accident airplane was reexamined in 2008, and similar firewall damage was found. The mechanical damage and marks were consistent with the engine mount contacting the bulkhead periodically before the accident. The new engine mount, which the manufacturer subsequently replaced under warranty on all PA 46-500TP airplanes, incorporates a heavy-duty, reinforced one-piece design at the actuator attach point, eliminating the two-piece design, which was previously produced in two-weld and subsequent single-weld versions. The reinforced, one-piece design provides a less compliant structure, which prevents relative motion between the two feet in the original engine mount design.

"This case was modified March 5, 2008."

History of flight

On January 16, 2007, approximately 1155 mountain standard time, a Piper PA-46-500TP, single-engine turbo propeller airplane, N747BL, experienced a nose landing gear collapse and loss of directional control during landing roll at the Parowan Airport (1L9), Parowan, Utah. The airline transport pilot, who was the sole occupant, was not injured. The airplane was registered to a private individual and operated by the pilot. Visual meteorological conditions prevailed for the personal cross-country flight, which was conducted in accordance with 14 CFR Part 91, and a flight plan was not filed. The flight departed the McCarran International Airport (LAS), Las Vegas, Nevada, about 1055.

In a telephone interview, and according to the Pilot/Operator Aircraft Accident/Incident Report (NTSB Form 6120.1), the pilot reported that during the approach to landing the red gear warning light remained on for about 4 to 6 minutes, but then went off. The pilot stated that at the end of the landing rollout and at a minimal taxi speed the aircraft [veered left], and impacted a snow bank off the side of the runway before coming to rest in an upright position. The pilot also reported that when the nose gear was lowered onto the runway, "...it started to shimmy a little bit before pulling to the left."

The pilot reported that 2 to 3 landings prior to the incident landing he noticed the airplane constantly pulling to the left on taxi and takeoff, and also during landing. The pilot stated that while taxiing he had to exert unusually heavy pressure on the right rudder to keep the nose straight, and at times he had to use braking to taxi straight. The pilot further reported that on a number of other occasions the landing gear warning light came on in flight and remained on for brief periods, and on one flight after lowering the landing gear the nose wheel indicator light was red; a normal landing followed without incident.

Personnel information

The pilot held an airline transport certificate with single and multiengine land ratings, and a commercial pilot certificate for single-engine seaplanes. The pilot reported a total time in all aircraft of 6,171 hours, with 181 hours in make and model. The pilot further reported having flown 60 hours in the last 90 days and 20 hours in the preceding 30 days. The pilot also reported having completed his most recent biennial flight review on November 3, 2006, which was conducted in a P-46-500TP Meridian turbo propeller airplane.

The pilot held a third class medical certificate dated April 24, 2006. Under limitations, the pilot's medical certificate stated the pilot must wear corrective lenses.

Aircraft information

N747BL, a Piper PA-46-500 turbo propeller single-engine airplane, serial number 4697226, was manufactured in 2006, and issued a Federal Aviation Administration (FAA) normal airworthiness certificate. At the time of the accident the airplane had accumulated a total of 181 hours. The airplane was equipped with the original engine mount, part number 102460-002, serial number 815909.

According to maintenance records the airplane underwent its most recent annual inspection on December 1, 2006, at a total airframe time of 162.2 hours. On November 17, 2006, Piper Service Bulletin (SB) 1154A, Engine Mount Inspection, was complied with: "...no cracks or defects noted." SB 1154A, dated July 26, 2006, stated, "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 SB 1154A requires the repetitive inspection of the engine mount. PART II requires replacement of the engine mount if cracks are found during the inspection of PART I. Compliance time was to coincide with the next regularly scheduled maintenance event but not to exceed 100 hours.

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.

Wreckage and impact information

The initial onsite examination of the aircraft, conducted by an FAA airworthiness inspector and a representative from Piper Aircraft, revealed that the airplane had sustained minor damage. Examination of the nose gear found that the rear actuator bolt was missing and the actuator was pushed against the aluminum rear wall. A subsequent search of the excursion area along the runway with a metal detector located the head end and the nut end of the actuator bolt. A subsequent examination by the NTSB Materials Laboratory in Washington, D.C., revealed that the bolt fracture signature was consistent with shear overstress. An examination of the engine mount with a flashlight from under the airplane revealed no damage or cracks.

Test and research

On March 21, 2007, a Senior NTSB investigator, 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 incident mount, 4 mounts from other accidents and incidents were examined (Ref: NTSB Accident/Incident Reports - DEN07LA030, MIA07LA038, CHI07IA067, and LAX05LA116). An examination of this airplane's engine mount revealed that the mount was bent near the nose gear actuator attach feet, and no cracks were noted.

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 that 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 included additional testing and analysis beyond the minimum levels required by the FAA in order 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. An engineering examination conducted by the NTSB IIC of a similar accident in Steamboat Springs, Colorado, and a NTSB structural engineer, found that there was compliance (flexibility) in the original engine mount and the STC mount and that this compliance issue was exacerbated at various speeds, sometimes resulting in a high speed shimmy effect and subsequent uncommanded left or right turn of the nosewheel during takeoff or landing.

The fractured AN-7 nose landing gear actuator bolt was sent to the NTSB Materials Laboratory in Washington, D.C., for examination. A Senior NTSB metallurgist reported that the bolt was fractured through the grip area about 0.89 inches from the underside of the hex head, with