Stopping corrosion before it stops mission

  • Published
  • By Jeanne Grimes
  • Oklahoma City Air Logistics Center Public Affairs
TINKER AIR FORCE BASE, Okla. (AFPN) --  Like cancer, it grows and spreads, risking men, machines and missions.

In the docks where E-3 Sentries are sidelined for programmed depot maintenance, workers are as skilled at eliminating corrosion and its risks as surgeons are at cutting out a cancer.

The work consists largely of inspections, checks and more checks.

“We check things that show a history of cracks or corrosion,” said Don Davenport, E-3 aircraft unit chief. “We start stripping areas as soon as the aircraft comes in here.”

That includes removing all flight controls, the main landing gear, and stripping the interior-forward and back-lower lobes.

“We tear the airplane completely apart,” Mr. Davenport said. “All the flight controls are routed to different shops to be repaired. The gears we work here in our area. We have our own gear shop.”

Numerous skills are needed when work begins on an E-3, including general aircraft, hydraulics, riggers, post dock, fuel, sheet metal, avionics and electrical, he said.

A corrosion-preventive compound is the treatment of choice when damage is found, Mr. Davenport said.

A crew applies the compound to the aircraft at night. Just one gallon of the coating can be applied per eight-hour shift, said Charles Alley, E-3 structural unit chief.

“What we try to do is inspect … leading and trailing edges first,” Mr. Alley said.

The compound is also applied to the crown skin on the top of the fuselage, Mr. Davenport said, as well as in the rotodome.

Visual inspections turn up problems such as loose or missing fasteners, stress cracks, structural damage and, of course, corrosion.

“We find a lot [of corrosion],” Mr. Alley said. “We’ve found some fuel lines almost corroded through. That was definitely a safety [issue].”

These are followed by X-ray inspection of some parts to find damage even the most discerning eye could miss. Those include window frames in the flight deck and portions of the main landing gear.

The corrosion and damage an aircraft brings into the dock largely depends on where the plane has been, officials said. Damp weather and salty air means more corrosion, as does a hot climate where the E-3’s air conditioning system runs more.

To perform all the inspections and make repairs requires sheet-metal mechanics working day and night for 74 days, Mr. Davenport said.

Mr. Alley estimated 75 to 80 percent of the actual sheet-metal tasks accomplished during the dock phase come about through the constant checking and inspections.

That percentage translates to an average 6,000 man-hours per aircraft.

Nolan Bush, an aircraft sheet-metal mechanic, knows corrosion in all of its forms. When an E-3 is in dock, his specialty is working tasks that target crown-skin corrosion and corrosion on stringers, stringer clips, rivets and panels.

“We do inspections for corrosion, determine what kind it is and from that determine the action to remove it,” he said.

In fact, there are four types.

Filform is the earliest stage and shows up on the metal as a powdery substance. One step worse, galvanic is a “white powdery flaking corrosion” while pitting shows up as “little black spots.”

“The corrosion is first starting to eat through the metal,” Mr. Bush said. “It works like an acid.”

Exfoliation means the metal is deteriorating and flakes apart.

“For exfoliation, we manually fabricate new parts,” Mr. Bush said.

The advance from filform to exfoliation can be rapid -- three to six months -- depending on how much moisture gets to the metal.

“Once corrosion starts, every day it deteriorates more and more. It’s just like a cancer,” said Mr. Bush.

“Metal is like a magnet to the water,” Mr. Bush said. “If you have one scratch on some bare metal and get water on it, corrosion will start.”

Mr. Bush said the compound has been used here since 1999 with good results.

“We’re getting those aircraft back now, and they look pretty good,” he said. “It’s general sheet-metal practice. We’ve made tremendous improvements in that area.”