LANGLEY AIR FORCE BASE, Va. –
On Dec. 3, 2007, the commander of Air Combat Command initiated a F-15 fighter jet stand-down order due to Air Force wide investigations revealing cracks in F-15 longerons. The stand-down lasted 44 days, and ended only after each F-15 was inspected using non-destructive inspection, (NDI) and deemed safe for flight.
The 1st Equipment Maintenance Squadron NDI examined each of Langley's 20 F-15s, which required a minimum 12 and a half hour inspection.
"I truly felt NDI was at the tip of the spear during the F-15 stand-down," said Tech. Sgt. Natalie Carlton, 1 EMS NDI craftsman. "We worked non-stop inspecting all the F-15s to ensure there weren't any cracks or defects. Our concern is for the safety of pilots and maintainers...to prevent aircraft mishaps."
NDI inspects for cracks and flaws on aircraft and their components, aerospace ground equipment, safety equipment and also tests jet engine oil samples, using a variety of methods, like magnetic particle, fluorescent penetrant, eddy current, radiography, optical and ultrasonic equipment.
Inspection times vary, depending on which method is utilized and the aircraft part being inspected, said Staff Sgt. Pamela Stegall, 1 EMS NDI craftsman. For example, fluorescent penetrant can take up to two hours, eddy current 10 to 15 minutes and oil samples one to two minutes.
The Pro Super, the liaison between the flight line and the back shops, tasks NDI with inspection orders. Orders are also called in from the Engine Shop, the Emergency Global Rescue, Escape & Survival System shop etc., Stegall said.
Aircraft parts always come in and out of their shop, and they also work directly on the aircraft on the flight line. Routine tasks arrive at intervals, depending on how many hours an aircraft has flown, and randomly if a crack or defect is suspected. Support equipment, such as the hooks that lift jet engines are also inspected for damage every few days.
Once a crack is found, NDI documents the length of the crack and then notifies the appropriate shops to have it fixed, Carlton said.
F-22 and F-15 engine oil sample analyses are done daily. Each engine must have an oil analysis done after the first flight of the day to indentify oil wear metals like iron, aluminum, silver, titanium, chrome and nickel. These metals determine what parts of the engine are defective or breaking down, Stegall said.
Sometimes aircraft take off before the oil samples are analyzed and must be called back because of bad test results, Stegall said. For the safety of the pilot, it is part of NDI's job recall the aircraft so it can undergo further inspection and repair.
"When an aircraft crashes, NDI is immediately put under investigation by the office of special investigations," Carlton said. "The last person who 'touched' the jet is held liable if a crack or defect was missed during inspection."
Inspection results can delay the mission for up to a few days, Stegall said. It depends on the severity of the crack or defect and what sort of repairs must be made. The positive, however, is that a part can be repaired instead of replaced.
NDI craftsmen always wear safety gear during inspections. While using hazardous chemicals, they wear gloves, goggles or a face shield and an apron. For x-rays, they wear electronic personal dosimeters and thermo luminescent dosimeters, types of radiation monitoring equipment.
"We're like doctors, taking care of the jets," Carlton said. "You feel like you're holding people's lives in your hands."