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Pickle Fork Inspections
Aviation Technical Testing, LLC performs pickle fork inspections for aviation clients to ensure the continued reliability of these critical components.
Aircraft wing-to-fuselage joints with active suspension (more commonly referred to as pickle forks, so named due to their distinctive shape) serve a fairly important role in the design of a plane — they fasten the wing spars to the fuselage. These components absorb many of the forces imposed on the wings during a flight, including torsion, bending, and vibrational stresses. Mounting two to each side of the body, with one in front and one behind the wings, allows the wings to flex in the wake of aerodynamic forces and prevents the joint from incurring fatigue damage.
Per the Federal Aviation Administration (FAA), issues with this part could undermine the aircraft’s structural integrity, while a mid-flight failure would be catastrophic since it will likely “result in loss of control of the airplane.” Due to these considerations, engineers place a great emphasis into the design of the component.
Reasons for Inspection
Pickle forks are designed as safe-life parts. This means they have a defined lifespan, after which maintenance must retire them regardless of whether they show signs of fatigue. Due to the essential nature of these components’ function, engineers design pickle forks to last the entire lifetime of the plane itself: 90,000 cycles of takeoffs and landings. Their design means airlines, pilots, and day-to-day maintenance should expect that the component will not show signs of impending failure before the 90,000-cycle threshold, by which point the plane itself should be removed from service. For these reasons, many in the aviation industry felt it disconcerting that pickle forks joining the rear wing spars to each side of the fuselage in certain aircraft were developing cracks in their failsafe strips roughly one-third of the way through their intended lifespan.
The issue presented itself around the 30,000-cycle mark, prompting further inspections and reporting to the FAA. The administration distributed an airworthiness directive (AD-2019-20-02) in response on 3 October 2019. In that directive, they ordered immediate inspections for airliners that had reached 30,000 cycles and belonged to the same manufacturer and generation as those with cracking damage. Furthermore, the FAA requires inspections within a year from the directive for those planes with 22,600 cycles or more. Finally, it mandates that airlines perform these inspections on the planes covered in this scope every 3,500 cycles going forward until the plane is removed from service. Airlines must report their findings, whether they discover a flaw or not, to the manufacturer so that both parties may pursue appropriate actions.
Performing these inspections thoroughly and correctly requires an NDT expert with a proven track record serving the aviation industry. AvTech offers these benefits through our world-class inspection services.
How AvTech Performs Pickle Fork Inspections
AvTech specializes in performing various methods of Nondestructive Testing (NDT) on aircraft to detect and/or characterize any flaws. Reporting required by the FAA includes noting the presence and location of any cracks on the assembly, whether in the fitting or the failsafe strap, on both sides of the aircraft. To verify the condition of an aircraft’s pickle forks, our inspectors use two methods: visual testing (often aided by borescope) and eddy current testing.
Most pickle fork cracking appears on the surface of the component and is thus visible to an inspector who understands precisely what they are looking for. Our veteran NDT technicians know their way around a plane and can easily locate the area in question. With proper access, they can view the part directly, make their assessment, and take pictures for directive-compliant reporting.
More often, however, the area cannot be directly accessed for inspection without some disassembly — which increases the time and cost associated with this mandated inspection. To make the process more convenient by minimizing the aircraft’s time out of service, AvTech’s inspection team regularly performs these visual assessments with the aid of a borescope camera.
A borescope consists of a minuscule camera, outfitted with a light source, mounted on the end of a tube that feeds either still images or full video to a display monitor. Using our flexible borescope, our technicians fish the lens through the gaps in the plane’s other components to reach the area of interest. The quality of resolution offered by this equipment allows AvTech inspectors to make sound judgments based on the high-definition images they view in real time. Furthermore, these experts can take accurate measurements of any surface cracking they find to help formulate the scope of subsequent repair operations.
When cracks are not readily visible to the naked eye, we will employ another NDT technique, eddy current testing. This equipment generates a magnetic field through a conductive coil by introducing an alternating current. When placed near a conductive surface, electrical induction will cause eddy currents to swirl in the inspection material, thus producing a second magnetic field local to the material. That second field gets distorted if the material features any discontinuities at or just below the surface, which the receiver can detect and display. Although the eddy current test requires direct access to the subject, it provides a more thorough accounting of flaws in the material than possible through VT.
The results of an eddy current test require interpretation by a technician trained for and experienced with the method. AvTech’s inspection team frequently performs ET for clients in the aviation industry for a variety of other applications, such as inspecting the following:
If your company needs pickle fork inspections from a trusted aviation NDT provider, contact AvTech today. We can help you maintain FAA compliance and ensure the safety of your aircraft.
