Although most of the inspections were visual, (besides the eddy current used on the boltholes mentioned previously) on the landing gear, two of the inspections used the magnet particle inspection technique. Dye penetrant was used for some of the attachment points on the vertical stabilizer and ailerons where researchers used a black light to look at the parts covered in penetrant paint.
By far, the most exciting and extensive inspection will be the complete teardown where the Cessna skin and all the fasteners will be removed, and what Dr. Cope refers to as the “forensic investigation” will begin. The wiring bundles will be tested using a loop resistant tester that can be clamped onto both ends of any wire bundle to check the resistance as well as a special insulation test.
Extensive testing, down to the microscopic analysis of section pieces will be done. Efforts will focus on determining the condition and characterizing the damage (corrosion, cracking, fatigue, etc.), especially in the critical areas identified by Cessna.
Cessna’s identification of critical areas for high-time, aged, commuter aircraft include the attachments where the horizontal stabilizer bolts to the aft fuselage, the vertical stabilizer bolts, and the attachment points for the rudder, elevators, and ailerons. There are a couple of locations on the lower spar cord of each wing too and inspections will take place on areas of the beam running down the fuselage. Taking a look at wiring bundles is crucial, as well as analyzing the wear and tear on system components including flight control cables, fuel lines, and hydraulic lines.
As plans for the disassembly of the 402A commence, excitement mounts for the lab’s second plane, a 402C, being donated this fall by Cape Air out of Hyannis, Massachusetts. Cape Air operates 50 402C models mostly running them on short commuter flights that don’t log many flight hours, but abound on cycles. The donation of this plane and the 402A are ideal since there is not much information on this type of commuter plane (running under part 135), yet it will fall under the FAA’s regulation.
According to Dr. Cope there are 210,000 airplanes out there in general aviation and he’s been getting lots of interest from 402 operators as they see how much work is involved with the supplemental instruction. They are very interested in the specific damaged areas in order to ensure their high-time planes don’t have similar damage. They also hope that the researchers can find different methods of inspection that will require less demanding maintenance and be less expensive. The two extensive procedures mentioned earlier found to be necessary by Cessna for the supplemental inspections along with the service kits are sure to be very expensive. In order to determine the level of inspection necessary, the researchers at the Aging Aircraft Lab have a plan. “We want to be able to compare what we would see in the inspections specified in the service manual,” Dr. Cope explains, “to what you see when you are able to take the airplane apart.”
Even so-called antiques, such as the two Cessna planes chosen for this research, will be examined “nose to tail, wingtip to wingtip,” and the information learned will answer airworthiness questions for many other make and model aircraft in general aviation, possibly revealing less invasive or less expensive inspection techniques to keep these planes and their operators ready to fly.Additional ReSource
National Institute for Aviation Research
Wichita State University
Dale Cope Ph.D. (316) 978-3204 or email dale.cope@ wichita.edu
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