FTW99LA045

During the landing roll, the nose gear settled onto the runway, and the aircraft veered hard to the right. Application of the left brake had no effect. The airplane skidded, exited the runway, struck a runway marker, and collapsed the nose landing gear. The steering actuator had failed, the hydraulic fluid was lost from the steering actuator, and the fuselage received structural damage. The steering actuator assembly, p/n 1501-4, had accumulated 5,938.0 hours since new and had not been repaired or overhauled. Examination of the nose gear steering actuator cylinder by the metallurgist revealed that the cylinder fracture was the result of fatigue cracking initiated by an abrupt machining transition from the 45 degree thread ring chamfer to the straight wall of the cylinder. The engineering drawings appear to depict the radius at the fatigue origin as a continuation of the 0.03 inch to 0.06 inch radius adjacent to the fracture. However, the drawing is not clear on the specific intent of the transition between the nearby radius and the internal threads for the nut.

On November 27, 1998, at 1405 central standard time, a Lockheed L-1329, 4 engine jet airplane, N787WB, impacted an airport sign and terrain following a loss of nose wheel steering during the landing roll on runway 13R, Robert Mueller Municipal Airport, Austin, Texas. The airplane was owned and operated by Banair, Inc., of Houston, Texas, under Title 14 CFR Part 91. The two airline transport rated crew members and the passenger were not injured, and the airplane sustained substantial damage. Visual meteorological conditions prevailed for the business flight which originated from Houston, Texas, at 1335. An IFR flight plan was filed.

The pilot reported hearing a loud pop as the nose gear settled onto the runway. The aircraft veered hard to the right and application of the left brake had no effect. The airplane skidded 978 feet before exiting the runway near taxiway Papa. The airplane struck a runway marker and subsequently collapsed the nose landing gear. The aircraft traveled an additional 120 feet before coming to rest. Upon examining the nose gear area, the pilot/mechanic and the FAA inspector found the steering actuator failed and hydraulic fluid was lost from the steering actuator. The FAA inspector reported structural damage to the fuselage.

A review of the maintenance records from May through November 1998, by the FAA inspector, did not reveal any entries specific to the nose wheel steering. The pilot/mechanic reported that the aircraft was scheduled for the AAIP (OPS #2) inspection to commence on November 30, 1998. He further stated that the steering actuator assembly, part number 1501-4, had accumulated 5,938.0 hours since new, and there was no history that it had ever been repaired or overhauled.

The nose gear steering actuator cylinder was forwarded to the NTSB Materials Laboratory for examination. The metallurgist reported that examination of the fracture surfaces found fatigue arrest markings on the majority of the fracture surfaces. The fatigue initiated at the inner diameter surface of the cylinder and progressed "rapidly" outward. The fatigue initiated at a multitude of origin sites and dispersed completely around the inner diameter surface. No evidence of mechanical damage was noted at the origins.

The fatigue origins were located at the abrupt transition from the 45 degree thread ring chamfer to the straight wall of the cylinder. The engineering drawing for the cylinder does not clearly define the machining details in this region of the cylinder, but shows a large radius without dimensions. The nearby radius between the cylinder wall and a vertical surface measured approximately 0.042 inches. The engineering drawing calls for a 0.03 to 0.06 inch radius. See the enclosed report for additional details.