NTSB Factual Report

On April 24, 2013, about 1720 eastern daylight time, a Piaggio P180 airplane, N139SL, received minor damage during a runway excursion at the St. Petersburg-Clearwater International Airport (KPIE), Clearwater, Florida. The air transport pilot and 5 passengers were not injured. The airplane received minor damage to the nose landing gear and wheel. The airplane was registered to Anoil Co. and operated by Avantiar under the provisions of 14 Code of Federal Regulations Part 91 as a business flight. Visual meteorological conditions prevailed for the flight and no flight plan was filed. The local flight originated from KPIE about 1550.

During landing, when the nose wheel touched down, the pilot heard the sound of a tire squeal and then felt the airplane gradually veer to the right. The pilot attempted to correct the turn by applying left rudder, left braking, and left engine reverse thrust. The airplane came to a stop with the nose pointed more than 90 degrees to the right of the runway centerline. Only the nose landing gear exited the runway.

The operator examined the nose landing gear after the event and performed multiple tests in attempt to determine the cause of the malfunction. When the hydraulics were turned on and the electric steering turned off, the steering actuator actuated the wheels 50 degrees to the right. When the electric steering was turned on, the steering actuator actuated the wheels back to the center position or 0 degrees. The steering manifold, serial number M/DAG74/04; part number 114180003, was removed from the nose landing gear and retained for further examination.

The nose landing gear and steering manifold were overhauled by Advantage Aviation Technologies II, LLC (AAT) on March 15, 2013. According to the AAT work order, the steering manifold was overhauled in accordance with Component Maintenance Manual (CMM) 32-50-50, Revision 6.

A post incident examination was conducted on the steering manifold. The purpose of this examination was to reveal any mechanical malfunctions or failures of the component. It was also to discover and evaluate the overhaul procedures used by AAT.

The testing procedures used by the group were the manufacturer's Component Maintenance Manuals (CMMs) which are the correct manuals to use when overhauling the landing gear and its components.

The feedback and control readings were all completed on an analog scale as provided by AAT, not a digital scale as specified in the CMM. The Test Box DRT66770, as specified in the CMM, was not available during testing and was never used by AAT during the overhaul because they do not possess one. A 1985 era Dowty-Rotol Ltd. wiring diagram, 460006820 - sheet 2 of 5, was located at AAT and was used to engineer a replacement test box which was used in all tests performed by AAT and by the group. None of the other required tooling and test boxes, as specified by the CMM, were available at AAT.

The steering manifold was first connected to an exemplar Piaggio P180 landing gear. With the system electrically de-energized and hydraulic pressure available the actuator steered left without any commands or inputs. The bias steering check was accomplished and the actuator always actuated to the left. The test was performed twice and the actuator arm moved 6 degrees the first time and about 14 degrees the second time. The tests did not replicate the uncommanded right turn as experienced during the runway excursion.

The steering manifold was then connected to a hydraulic test rig and tested per CMM 32-50-50, Revision 8, which was the most current revision at the time of the examination. The group decided that the tests were invalid because ATT did not possess the specified test box. The manifold did not pass any of the other CMM functional tests because the solenoid valve inside the manifold would not close properly.

The manifold was then disassembled and examined in order to reveal any anomalies inside the unit that would not allow normal operation.

The examination revealed multiple scratches and damage noted to the armature plate and retainer ring. One wave washer and two shims, which measured 0.003 inches in thickness, were located inside the sleeve assembly. The wire connected to the electrical connector was damaged and had a white insulation sleeve placed over it, which ATT had installed during the overhaul. The installation of the insulation sleeve was not a specified procedure in the CMM.

A review of the original overhaul paperwork revealed multiple discrepancies. ATT omitted procedures during the overhaul. AAT used alternative tooling which was not approved by the CMM and not referenced in the overhaul paperwork. AAT did not possess any written procedures to which they worked from to validate that the work was completed properly.

The manifold was not able to be tested as required in the CMM, as the overhaul facility did not possess the required equipment and tooling and testing equipment.

NTSB Probable Cause

The failure of the nose landing gear steering manifold during landing, which resulted in an uncommanded and uncontrollable right turn, and the overhaul facility’s improper overhaul of the nose landing gear steering manifold.