TINKER AFB, OKLAHOMA --- The recent discovery and repair of corrosion on a structurally-crucial part in 15 KC-135 Stratotankers, accomplished jointly by several units at Tinker Air Force Base, has increased the safety of the fleet and gained recognition by high-ranking Air Force officials.
In April, an aircraft was being prepared for return to its unit following programmed depot maintenance, when a mechanic in the 76th Aircraft Maintenance Group was in the wheel well — a space the size of a small closet — and noticed about 1.5 inches of corrosion on the keel beam.
Mostly hidden by other structural components, the keel beam runs along 5 to 6 feet of the body of the KC-135, supporting the floor of the aircraft.
While it was initially thought replacement of the beam in all 15 affected aircraft would take a year, the work and coordination of several units on base led to the project being completed in less than six months.
“We went through all this process way faster than we thought we could … because of the professionals (working on it) and (their) talent, but also because of the teamwork between the different entities,” said Col. Mark Moccio, KC-135 system program manager.
Following the initial discovery, the other KC-135s located at Tinker AFB were inspected, with some in the same condition.
Moccio said the discovery was alarming, because the corrosion had never been discovered or worked on before, and the failure of the beam would be catastrophic.
“We got nervous that this was a widespread problem throughout the fleet, and because of where that piece of metal is, if you can’t determine how much is corroded, then you had to ground the airplane,” Moccio said.
A one-time inspection of the 396 aircraft fleet was initiated, and affected aircraft not already at Tinker AFB were immediately grounded. Planning began immediately for them to arrive at the installation one at a time for repair.
Members of the 553rd Commodities Maintenance Squadron and KC-135 System Program Office became involved to coordinate the removal, manufacturing and replacement of the beam, none of which had been done before.
Jordan Johnston, PDM Liaison Engineer for the KC-135 SPO, led efforts of removal and reinsertion of the keel beam — not an easy task considering its placement within the aircraft. “We were really afraid when we were looking at this, because of the level of disassembly that was going to be required, but everyone was spot on,” Johnston said.
Additionally, the work had to be coordinated simultaneously with scheduled PDM being performed on KC-135s not impacted by the corrosion.
When it came to manufacturing replacements for the beam, the 553 CMXS ran into immediate challenges as well.
Acting Squadron Director Kristy Jordan said the manufacturer of the material required for production of the keel beams would not deliver for 12 weeks.
Additionally, while the squadron is “no stranger to urgent needs” when it comes to organically manufacturing aircraft parts, Jordan said, the keel beam is particularly complicated, requiring “complex machining and elaborate joggling” of the metal.
“(The keel beam) is standard aircraft aluminum, but some of (the) angles are pretty complicated, and (there’s) all the holes in it. There’s a lot of fasteners in it,” Moccio said. “Some of these (aircraft parts) are not made to be removed … This was one of those cases.”
The squadron found the material they needed in a thicker form they could machine down to the correct dimensions, cutting the material delivery time from 12 weeks to two, then several shops worked together to create a prototype beam in just two weeks, Jordan said.
“For us to quickly model, machine and joggle it correctly…(it was an) innovate and persistent attack of this problem,” Jordan said.
While it initially took 21 to 30 days for 76th AMXG to remove and replace the beam, the process was quickly reduced to 14 days, and the group worked with the KC-135 SPO to coordinate the aircraft coming in for repair on schedule.
With work beginning on the fleet in June, the last aircraft was completed in late October, both ahead of schedule and without disrupting the flow of the PDM line, Moccio said.
Completion of the replacements prompted Gen. Maryanne Miller, commander of Air Mobility Command, to email Moccio and a number of other people involved in the project, recognizing their efforts to expedite the process.
Jordan said the success of the replacement of the keel beams was facilitated by the shared mission focus across units and prevention of the project being siloed when problems arose.
“There was no room for ‘this is too hard, this is complex, we can’t do it.’ It was never ‘if’ we are going to be successful, it was a matter of how quickly we were going to arrive at that success,” Jordan said.
Johnston said the challenge highlighted the kind of team that has been built at Tinker AFB.
“It’s not something you will notice on a day-to-day basis, but it really demonstrated how well everybody is working together because of how quickly we were able to respond to it,” Johnston said.