Pivotal success

Published Sept. 18, 2009
By Howdy Stout
Tinker Public Affairs

TINKER AIR FORCE BASE, Okla. -- A B-1 sits in the hangar surrounded by scaffolding. Stripped of paint, the aluminum skin glistens under the work lights as mechanics reach inside access panels or consult technical orders. "It pretty much has all the references," says aircraft mechanic Tate Valentine of the technical orders. "But just like any TO, it can be vague."

But Mr. Tate and others are helping to write the book on a procedure that might become standard practice on the B-1B bomber. With its complex variable-geometry swing wings, mechanics are learning how to remove the pivot pin that allows the bomber's wings to move in-flight. "It is a very interesting project," Mr. Valentine explains. "It is impressive; the planning, the scheduling, mechanics and everything involved. It's a major project and it's something Tinker should be proud of."

Developed as a nuclear strategic bomber in the 1970s and put into service in the 1980s, the B-1 now serves as a conventional bomber, using its impressive bomb capacity and long range to strike at the Taliban. But as the aircraft ages and continues flying combat missions, engineers and mechanics are performing maintenance tasks not originally envisaged. One of those tasks involves removing the critical pivot pins for inspection and, if need be, replacement. It's a big job.

"We've done it a couple of times," explains Mr. Valentine, who was one of a group of Tinker mechanics who journeyed to Guam to remove and replace a fire-damaged wing from a B-1. The project, which involved removing a pivot pin, took nine months and used techniques developed on test aircraft at Edwards Air Force Base, California.

Since then, mechanics at Tinker have removed, inspected and replaced a pair of pivot pins on a B-1 aircraft undergoing maintenance. This is the second aircraft.

"We're doing two aircraft a year for two years," explains shop supervisor Roger Walker. If engineers find significant wear, the pivot pin inspection will become mandatory throughout the B-1 fleet.

For some, the project is on-the-job training.

"The whole thing is stressful," says aircraft mechanic Clifton Chenevert.

To reach the pivot pins, the mechanics must remove the B-1s four engines and engine nacelles. That also means disconnecting and draining fuel lines, hydraulic lines and fire extinguishing bottles. It's a time-consuming process that leaves the ordinarily sleek aircraft "looking like a lawn dart," Mr. Valentine says.

"We probably have more trouble disassembling it than pulling the pin," explains aircraft mechanic Randy Orr, who along with Mr. Valentine, are the only aircraft mechanics versed in the pin-pulling procedure.

Once the engines and nacelles are removed, the wings themselves are braced so they won't move when the pins are pulled out. With everything in place, a crane is attached to the huge, 800-pound pin.

The area around the pin is wrapped in a thermal blanket and heated to 120-degrees Fahrenheit. Heated for at least four hours, the parts expand.

"We use a big thermal blanket to heat the structure," Mr. Valentine says.

"And then we freeze it," says Mr. Chenevert.

Although large, the pivot pins are hollow. "You could almost put a person inside it," Mr. Chenevert says.

Liquid nitrogen is pumped into the interior of the pins, where the extreme cold causes it to shrink in diameter. The crane maintains pressure on the pin throughout. The liquid nitrogen is poured in slowly, with mechanics plugging holes and leaks with balsa wood and RTV silicone.

"We have full gear on," says Mr. Orr, "aprons, gloves and face shields."

"We put a press on (the pin) to maintain pressure," explains Mr. Valentine. "As the pin itself shrinks, it pulls away from the heated structure and everything just pops out. A little heat, a little cold, a little pressure and a little time."

It only took 30 minutes to pull the pins on the first aircraft to undergo the treatment. "We were pretty fortunate on that one," Mr. Valentine added.

Once the pin is removed, the surrounding bearings, bolts and fasteners are also pulled out and replaced as needed. The inspection of the pin itself takes no longer than a day.

Then the mechanics get to put it all back together.

The pin is immersed in liquid nitrogen to cool and shrink. Then it is a race against time. Because the space between the pin and surrounding structure is less than a thousandth of a micrometer, the reinstallation of the pin must be done quickly and correctly before the pin heats and expands. "We soak the pin in there for a couple of hours," Mr. Valentine says. "And the clock's ticking. Once you pull it out of the nitrogen, it has to be in and perfect."

"You have to have it sitting in their right or else," Mr. Chenevert adds.

There are 16 different measurements to be performed to ensure the pin is correctly installed. Dental putty is used to make the measurements as the area is too inaccessible to measure otherwise.

And if it's not right?

"We have to reclock it," Mr. Orr says.

Work on this, or any other aircraft, needs to be done properly, Mr. Chenevert says, because if it breaks "you can't just pull to the side of the road."

"It's a responsibility," says Mr. Orr.

"You have somebody else's life in your hands," Mr. Chenevert continues. "It's not for everyone. It's not putting bicycles together at Christmas."

Even if an aircraft is fully reassembled, the mechanics will pull it apart if there is any doubt to the accuracy or safety of the work performed.

"Morally, you don't have any choice," Mr. Chenevert says. "There's no guessing game. It's either good or it isn't."

Although Mr. Orr calls the B-1 the "Corvette of the bomber fleet," keeping the corvette airborne takes its toll.

"It's an intensely difficult plane to work on," Mr. Valentine says, with many areas difficult to access for the mechanics.

The pace of the work has also increased. Normally, the mechanics will work on 11 aircraft per year. They've already hit that mark by the end of July and they have taken on four more aircraft, including the two needing pivot pin inspections. They've lost many experienced mechanics to retirements and promotions. Most of the mechanics work overtime, six days a week, to get the planes back into the fight.

Mr. Valentine and Mr. Orr, who both joined Team Tinker at the same time, are used to the long hours. Mr. Valentine is managing to take 13 credit hours of college classes while Mr. Orr is building his family's home in anticipation of his latest child.

"We hired on together and worked E-3s and B-52s and it's been that way at every weapons system we've been on," Mr. Valentine says. "B-1s traditionally haven't had a lot of overtime until this year. It could be worse."

Work for the first shift starts at 4:30 in the morning. The three shifts are busy around the clock, doing the work of twice their number. But help is on the way with the recent hiring of 20 new mechanics.

"They've done a heck of a job," says Mr. Walker, watching the mechanics reinstall the ejection seats on one of the bare-metal B-1s. Today they might work on one aircraft, the next day another. The work doesn't stop. "They've gone way and above," he continues. "We have a mission to help protect our country and these guys have done a heck of a job."