Source: United States Navy
A process developed and refined at Fleet Readiness Center East (FRCE) is producing positive results in the maintenance, repair and overhaul of the CH-53E Super Stallion and MH-53E Sea Dragon heavy-lift helicopters serviced at the depot.
A team of engineers and artisans from the H-53 Aircraft Components Shop worked together to improve the manner in which the aircraft’s spar fittings are evaluated for fit, resulting in a higher acceptance rate and faster turnaround times for the components. The spar fittings fasten the helicopter’s horizontal stabilizer to the tail pylon, allowing the horizontal stabilizer to prevent the helicopter from experiencing excessive up-and-down pitching during flight.
The new process uses a pressure plate and pressure-sensitive film to clearly identify high and low areas on the mount feet of the two inboard metal spar fittings in the horizontal stabilizer, which affix to corresponding mating surfaces on the tail pylon. These mount feet must make 80% contact, with no gaps larger than two-thousandths of an inch, said Jason Gaskill, an H-53 airframe production support engineer with the Maintenance, Repair and Overhaul Engineering Production Line Support Division at FRCE. Spar fittings that cannot meet the required tolerances must be removed from inventory and replaced with new fittings, which are either purchased from commercial manufacturers or produced by FRCE’s machine shop.
These tight tolerances require an incredible level of precision work from the machinists who blend the surfaces of the reworked fitting; the bright pink dye left behind following a fit check using the pressure-sensitive film gives the machinists a visual indication of exactly where they need to grind. It works in much the same way as dentists use articulating paper, also known as bite paper, to identify where teeth contact during biting and grinding, he said.
“Many of these fittings have undergone years of maintenance, from removing superficial corrosion with a scouring pad to machinists grinding and blending to remove minor corrosion,” Gaskill explained. “If it’s not a new fitting straight from the manufacturer, somebody has removed minor corrosion at some point. And when you’re talking measurements of a thousandth of an inch, the machinists don’t have a way to judge exactly which areas of the fitting they’re removing material from, or whether they’ve removed the exact same amount of material from one of the surfaces compared to the other one.”
Because the human eye isn’t able to measure increments that small, Gaskill said, the team sought to develop a process to let the machinists know exactly what type of work needs to be done to the stabilizer side of the fitting.
“Now we can give them a visual representation of what areas require blending and how much needs to be taken off,” Gaskill said. “We wanted to put in place a good, solid process so we know that what the shop is putting out is a good product without 100% replacement of these fittings.”
The process for using pressure-sensitive film to verify contact on the stabilizer side fittings, for both leading and trailing faces, has been rigorously tested by engineers at FRCE and written as a temporary engineering instruction, which means it is now approved for use within the H-53 Aircraft Components Shop.
Saving the reworked fittings that are brought into tolerance has multiple benefits, Gaskill noted. It saves taxpayer dollars by avoiding the cost of a new fitting and reduces turnaround time for the H-53 aircraft in work on the depot’s H-53 production line.
Amy White, an aircraft examiner on the depot’s H-53 line, said the cost of replacing the spar fittings could run as high as $150,000.
“Before, if the gaps were bad, we just had to replace them,” White explained. “Now we’re able to save many of them, between what the machinists are doing by sanding down the pink, taking another impression and seeing where we are, maybe sanding some more.
“Once we get to that 80% contact, we’re good to go and we’ve saved those fittings,” she continued. “And we spent labor hours working on it, instead of $150,000 in materials plus the labor cost of replacing the fittings within the components.”
Paul Guthrie, sheet metal work leader in the H-53 Aircraft Components Shop, said the new process also supports an improvement in personnel utilization.
“Instead of having to change out that fitting, we can spend a few hours checking the spar fitting and sanding it down in hopes of saving it,” Guthrie said. “We can do three to four impressions with the pressure-sensitive film as the process goes along and, if by that point, the fit check hasn’t reached 80% contact or at least shown significant improvement, that’s when a decision is made. If we don’t see a major improvement or it’s too far out of tolerance or specification, then we have to get a new fitting.”
This verification of flush mating surfaces on the spar fittings’ mount feet also helps reduce overall turnaround times for H-53 aircraft maintenance at FRCE, Guthrie said.
An out-of-tolerance spar fitting leads to fitment issues when it’s time for the H-53 production line to connect the stabilizer to the helicopter’s tail pylon, which in turn slows down production on the aircraft line as the fitting has to be reworked or discarded and a new one procured or produced, Gaskill noted.
“That’s why I really wanted a process that could address this in the back shop,” he said. “Because if we don’t address it in our shop, then when the H-53 line is ready to install the stabilizer and it doesn’t install properly, that holds up their work. It’s a hard stop.
“I feel really good about this process,” Gaskill continued. “It gives the components shop the ability to say they know the stabilizer side of the fitting is not the problem, and they have the technical data to back that up. And it allows us, as engineers, to know we need to look elsewhere to address the issue. One of the things we like to do as engineers is eliminate things that aren’t the problem so we can focus on what it could be, rather than every potential possibility.”
Gaskill said the team developed the initial idea for the process after discussing the spar fitting fitment issues with a senior engineer, who mentioned that the depot’s composite shop used the pressure-sensitive film to check for gaps between the composite layers of bonded tee caps, another fitting found on the H-53. While the spar fittings involve metal-to-metal contact rather than composite materials, Gaskill thought the same concept could work.
“I was trying to think of a way to get all of the high spots on the fittings sanded at one time and, with this, we didn’t have to reinvent the wheel. We’ve got a source of supply for the film. We had the plate from another process, although we are now working on getting a plate just for this specific use. We started with some trial runs and it turns out that this just works really, really well.”
MRO Engineering Department Head Thomas Osiecki said the development of this process provides an excellent example of how cooperation between MRO Engineering and the depot’s production elements leads to improvements that benefit both the FRCE workforce and the nation’s military aviators.
“It’s exciting to see the success that Jason and the FRC East team have experienced in establishing this method of identifying and correcting gaps on H-53 spar fittings, and the positive impact it’s having on cost and turnaround time for H-53 maintenance,” Osiecki said. “This is just one example of what our FRC East MRO Engineering Department team members do every day – they support the Fleet by helping improve maintenance outcomes in our component shops and aircraft lines. The FRC East teamwork on display with this effort helps speed delivery of components and aircraft back to our warfighters.”
Looking forward, Guthrie said he hopes other entities within the depot and beyond might be able to look at what the H-53 Aircraft Components Shop has done with the pressure-sensitive film and find uses for it within their own areas, as well.
“This film is a pretty readily available commercial product, it’s fairly easy to use and is giving us great results,” he said. “There may be someone out there in the facility or even in the Fleet that will say, Hey, we could do that too – just like our engineers picked up the idea from composites,” he said. “And if someone else has this same type of problem, they could easily try this process and see if it works.”
In fact, the H-53 Components Shop is now conducting trials of the process on the tail pylon spar fittings, and hope to see an approved temporary engineering instruction released in the near future.
“Of course, those fittings have never been checked this way, either,” White said. “And that’s important, because we can bring all these stabilizer fittings into tolerance but, if the fittings on the tail pylon are out of tolerance, it’s not going to matter what we’re doing to the stabilizer side. Using this process on the tail pylon side is another way to save time and cost for both FRCE and our customers in the Fleet.”
For Gaskill, the best part of this process development is knowing the artisans in the components shop are turning out the highest possible quality product for the H-53 line and customers in the Fleet.
“When we finish that horizontal stabilizer, we know that it’s good to go for mounting to a tail pylon,” he said. “And I just can’t praise the artisans enough. They took a process that they’ve never done before, and now they’re able to get these done so efficiently. They’re doing such a great job, and this process wouldn’t be where it is without them.”