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Fit to Fly: KC-135 ISO Preparation

  • Published
  • By Staff Sgt. Adam Goodly
  • 22nd Air Refueling Wing Public Affairs

The KC-135 Stratotanker has been in service for over six decades and in order to keep this aircraft in operation they must undergo routine inspections, which checks every valve, gear and panel to make sure they are at peak performance and mission ready.

Every 24 months, 1,800 flight hours or 1,000 landings, each KC-135 must undergo a thorough inspection known as an isochronal periodic preparation and inspection; also referred to as an ISO or PE. This type of inspection usually lasts 21 days.

“The periodic inspection is crucial to preserving the integrity of the KC-135,” said Staff Sgt. Wesley Koonce, 22nd Maintenance Squadron inspection section floor supervisor. “Much like a race car has a pit crew to keep the car going during the race, we have flight line crew chiefs. The time spent between flying missions is the time we need for an in-depth look at the aircraft; the periodic inspection is that in-depth look.”

During the ISO, a KC-135 goes through three different phases of inspection: preparation, inspection and fix.

Once the aircraft arrives at the hangar, the first step in the inspection process is to remove all the aircraft panels on the aircraft and complete axel inspections on the tires. This part of the process takes about two days and involves the maintenance team taking the wheels off and making sure there are no cracks or dents on the axels. On day two, larger components of the aircraft are taken off for inspection such as the nose and the tail end of the aircraft.

The inspection phase, is the second and the longest, usually lasting about 12-15 days. This phase is broken down into four areas of inspection: the nose, the two wings, and the tail.

“I coordinate maintenance actions in area 3, which is the right wing of the aircraft,” said Senior Airman Justin Eisentrout, 22nd Maintenance Squadron periodic inspection section area lead. “We start by taking the necessary panels off the wing and route them to other shops for repairs or adjustments and then begin the inspection. We also go over flight controls, the main landing gear on the right side and everything in between. I coordinate with as many as 5 different flights to prioritize the completion of any job that requires attention in my area.”

The third, and final phase for the ISO, is the fix phase. During this period, everything that was written up to get “fixed” during the inspection gets replaced and ultimately fixed.

After the aircraft completes all three phases of inspection, engine runs are done to check the engines and then the aircraft is sent to Fuel Cell and Corrosion to be checked for leaks and paint damage.

An ISO is only the half-way point for aircraft inspections. ISO’s happen every two years, whereas a depot inspection is much more thorough and that takes place every five years. That’s the most in-depth inspection that is done on a KC-135.

 “We are not only ensuring that the aircraft will be able to complete its mission, we are performing maintenance that will extend the life of an aircraft that is already more than 60 years old,” said Sergeant Koonce. “Through extensive inspections of major and minor aircraft components, over a four-week process, we are able to maintain mission readiness for an aging fleet.”