Defense

March 13, 2017
 

F-35 SLLP modifications completed

Kari Izatt, F-35 Lightning II maintainer, tightens bolts on the Lower Fuel Panel prior to the last Structural Life Limiting Parts (SLLP) program F-35 aircraft being rolled out of the depot maintenance hangar.

Men and women of the 570th Aircraft Maintenance Squadron at Hill Air Force Base, Utha, completed the last F-35 aircraft scheduled to receive a forward wing root rib modification under the Group 1 Structural Life Limiting Parts (SLLP) program.

This driving modification started with the arrival of the first F-35A at the Ogden Air Logistics Complex in September 2013.

Initial computer modeling showed the wing root rib could be subject to premature failure and the component was identified for replacement with a new, stronger alloy part.

Over the past three years the squadron received and completed a total of 22 SLLP aircraft.

Two of the aircraft were F-35A models from the Netherlands and two were Marine Corps F-35B STOVL (short take-off vertical landing) aircraft that arrived with only six days’ advance notice. Both F-35B aircraft were completed in time to meet the Marine Corps’ F-35B Initial Operating Capability milestone they promised Congress.

All aircraft needing this modification had a flight hour lifespan limit and with the new root rib parts installed, each aircraft can now expect to reach its full 8,000 flight hour service life.

To replace both left and right segments on the aircraft took significant disassembly and low observable restoration and this team completed the work in just under 3,000 hours per aircraft.

To make for more efficient and cost-effective work loading during this driving modification, the Joint Program Office scheduled aircraft for additional depot-level work during their stay.

During the past three years, the program grew from an average of six modifications, totaling approximately 6,000 hours per aircraft, to between 9 and 18 depot-level modifications, totaling between 8,000 and 11,000 hours per aircraft.

The last Structural Life Limiting Parts (SLLP) program F-35 forward wing root rib modification area is shown in primer paint prior to having low observable material reapplied. Removal of parts from this section were needed to gain access for the modification.

Other benefits gained during the mods include a cut in Supplier Quality Assurance Reports by 87 percent over the modification’s lifespan and a reduction in modification time by 27 percent.

Known as a 5th generation fighter aircraft, the F-35 presents many new engineering challenges to depot maintainers.

The most prevalent challenge faced includes on-aircraft drilling tolerances measuring less than 0.003 of an inch when it comes to margin of error. This has been further challenged as engineering data on the F-35 is still getting captured and, for this reason, standard depot practices to allow for standard repairs or oversize fasteners does not yet exist.

Greg Hoffman, 570th Aircraft Maintenance Squadron director, said, “This program has been one of the most challenging structural mods I have seen performed in my career in aircraft maintenance and certainly on the F-35. The men and women of the 570th Aircraft Maintenance Squadron and the members of Team Hill who support us can be proud to have been part of the first chapter in the F-35’s legacy within the U.S. Air Force.”




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