'Batman' fix to sustain C-5s for decades, saving millions

  • Published
  • By Jenny Gordon
  • Robins Public Affairs
Robins has hit another milestone by being the first to complete a new major structural repair on a C-5M which will bring in millions of dollars in revenue and sustain the Air Force's fleet for decades to come.

With completion of the first prototype in September, an additional 51 C-5s will need the new fitting by 2020. The retrofit is also of importance because it keeps the colossal weapon system flying safely. 

In the beginning

Following a structural fatigue analysis of the C-5 involving stress, cracks and corrosion, engineers from Robins and Lockheed Martin found that the life expectancy of the 'Batman' fitting was drawing to a close.

The Batman fitting is aptly nicknamed due to its resemblance to the costume headpiece worn by the fictional comic book character. 

Weighing about 80 pounds and measuring 10-feet wide and 4-feet high, it's the primary structural component that holds the front part of the tail structure, the vertical stabilizer, to the aircraft's fuselage.  

You can't fly the plane without it

"As part of the process to keep the aircraft flying for the next 40 years, this was one of the steps taken to make that happen," said Andy Ivey, 559th Aircraft Maintenance Squadron planning chief.  "After analysis it was discovered when having problems with this area, we needed to do a fleet-wide change to this particular fitting because it's a high-risk area for aircraft structural failure."

Field-level inspections in 2009 identified cracks that were occurring in several aircraft, normally indicative of a fatigue problem. Temporary repairs were made to ensure safe operations.

While recurring field-level inspections were made, Robins and Lockheed engineers were conducting analysis to see what was causing the cracks.

"The fitting was designed from a static-strength perspective. From a fatigue perspective and original design, one of the big considerations was weight," said Russ Alford, C-5 chief engineer. "As part of identifying and fixing the problem, we redesigned the fitting and thickened it up in places where cracks were occurring."              

One of the challenges for the replacement was that the original installation drawings did not account for the aircraft's skin and vertical stabilizer being in place. 

"To do it now, we had to develop a process on how to remove the Batman fitting without damaging the surrounding structure, and then put in the new fitting. That was a new challenge," he said.                         

Off to work we go 

The first aircraft identified to receive the Batman replacement fitting, once it completed its regularly scheduled programmed depot maintenance, entered a hangar on June 18. 

It would take exactly 108 days with 5,000 hours of work invested from start to finish before returning home in late September to its customer at Dover Air Force Base, Del.

The aircraft was placed on jacks, its horizontal stabilizer removed, dorsal panel taken off, flight cables rolled back, stands constructed for mechanics to work inside, existing fasteners tied to the old Batman fitting removed, and non-destructive inspections conducted on the Batman fitting's substructure prior to its installation. 

And that was just the beginning 

But first things first. When putting in a major new structure, you must take out the old, in this case the old Batman fitting. 

Since there was no process to begin with, teams from maintenance and engineering had to get together and form one. Constraints were identified and issues were brought up during a rapid improvement event, attended by engineers, planners, schedulers and mechanics. 

Michael McUmber, a 559th AMXS sheet metal mechanic, was one of four day-shift mechanics dedicated to removing the old material, bolts and the like, and passing them through a small opening called an anti-hijack screen door, located just under the tail section of the aircraft.

"After we removed the old fitting, we basically fit-installed it to see if it would fit," recalled McUmber. "Amazingly, it fit perfectly." 

That's not to say everything in those 108 days was smooth sailing. Engineers had to create new blueprints for mechanics to follow. Procedures had to be tested to see what would work best. 

"We resolved a lot of issues, especially with the blueprints," said Isaac Cruz, 559th AMXS tactical planner. "Keep in mind these prints were established a long time ago, and they showed outdated parts in there. We had to make a lot of changes to these prints.

"One of the main issues involved the parts listing for things like hardware, nuts, bolts, washers, etc.," he said. "Some of these items were so outdated that they were not stocklisted, so engineering had to research what was currently available and determine a suitable substitute." 

Fasteners used on the fitting had to be updated. New holes had to be drilled on the fitting, made of a new aluminum alloy that is much more resistant to corrosion and fatigue.  

"Secondary structures like fasteners, webs, none of that fit," said McUmber. "Those parts had to be remade by hand. Once that happened, then it was just a course of back-drilling everything in and locating holes on the Batman." 

To drill up the actual Batman fitting took about two weeks.               

Looking ahead

Space is a precious commodity when working inside a military aircraft, even on an aircraft as big as the C-5. It can get cramped. It's dark, and there can be tight awkward turns which can make things uncomfortable at times. 

When installing the Batman on this C-5M, there was a distance of about 12 feet from the floor to the top of the aircraft. With access stands in place, there's even less room for maneuvering.  

Made of stainless steel, mechanics had to drill in a dorsal longeron or shelf, which would tie everything together from the inside as well as outside. That consisted of four parts all fitting perfectly and safely together - the vertical stab, tail on the outside, Batman fitting, forward spar and dorsal shelf. 

After carefully documenting each step of the process with the initial aircraft, it's expected the days to accomplish the second one will be significantly less. The goal is to install the second Batman fitting from start to finish in less than 75 days. The team is optimistic. 

"We learned that this can be done in a timely and cost-effective manner," said McUmber. "Going in, we just didn't know what to expect." 

Cruz, who was in on the project from the beginning, credits mechanics like McUmber who dug right in. He also gave a nod to hydraulics technicians, the weight and balance shop and flight control mechanics.

"It took an entire team to do this," he said. 

Dave Nakayama, 559th Aircraft Maintenance Squadron director, told crews working on the fitting to be extra vigilant in tracking the project, taking things slowly and asking questions along the way. 

"We have to nail down this new process based on this prototype so we can become much more efficient, much faster when we go into full-scale production," he said.

  "The airplane has never been older than it is today, yet we have some of the highest mission-capable rates, some of the highest aircraft availability rates than we've had in 15 to 20 years. That's pretty fantastic," he said. "From what we're being told, this Batman fitting and dorsal longeron modification will keep these planes safely flying for at least another 30 years."

Starting in early 2015, they will do the process all over again - 51 more times to be exact - which should keep things pretty busy here over the next five years.

"This Batman fitting is a good example of what we do here. No one else in the world can do this. The fact that we're able to sustain equipment like the C-5 fleet is hugely beneficial to us as a country, to the Air Force and the Department of Defense," he said.