"On the chrome finishes, the main causes for rejection are corrosion, scoring, and wear. What we actually do is check the cylinder for wear to make sure it's within acceptable dimensions. Scoring that cannot be felt with your fingernail and can be buffed out on the lathe is reusable. Otherwise, any scoring that is beyond buffing out is cause for rejection and requires re-plating. Discoloring is typically not a problem and can easily be polished to look like new."
He continues, "The Beech manual is quite vague. It says to look for grooves and gouges and doesn't really give any limits. We reject anything that cannot be polished out or re-plated. The upper housing is actually quite forgiving in terms of gouges and dents. We can usually remove most minor damage and blend-out most nicks that are within reasonable limits."
Gramzinski says that it is also prudent at overhaul to replace all hardware and seals — this includes all nuts, bolts, clips, seals, etc. "It's not worth having the entire assembly fail for a nut that costs a few dollars."
A typical overhaul on the landing gear can be accomplished within five days, unless the components need re-plating. Re-plating of the chrome will add another two weeks to the overhaul process. But, because PAA typically have many replacement components in stock for the 1900, it can usually incorporate a reconditioned part from its inventory into the overhaul and complete it within the five-day period.
Repair techniques save $
"We have worked hard over the years developing repairs aimed at saving our customers money. We have developed several FAA-approved process specs for re-plating bores and re-anodizing shafts and bushings to restore the original dimensions to many components that would otherwise be thrown away. This requires an investment in engineering and FAA red tape, but it's worth it to reduce overhaul costs," he says.
For instance, PAA has developed a repair for the bore of the torque link attach points, for which it was having to throw away the cylinder or strut.
"This was a $5000 part and we decided to machine out the bore and install a bushing. We had the repair engineered and approved by the FAA and use it regularly."
Some repair schemes are not quite as simple as installing a bushing. Some are in critical areas where material cannot be removed to accomplish the insertion of a bushing. "This is why you've got to make an investment in engineering and determine what can and cannot be done," he says. "A recent study we did for one of our airline customers determined that through incorporation of all of our repair schemes, they saved just under $300,000 in a period of two years."
Repairs offered by PAA include bushing repairs to the upper main gear and nose gear housing, and the lower nose strut, repair of internal bearings in the nose cylinder, replating and repair of the axle assemblies, and re-chroming of the tube assemblies. A recently added repair is the replacement of the phenolic coating on the main gear lower bearing. "This bearing costs around $300 to replace. We have developed a procedure to reline this bearing with new phenolic — cost is around $110."
Protection from corrosion
Gramzinski says there are several steps that can be taken to keep the landing gear from corroding severely during the next in-service period.
One of those is to use a poly-amid epoxy primer instead of the traditional zinc chromate. This epoxy hardens to create a very durable corrosive-preventive primer and is a great improvement to the zinc chromate used by many shops.
"We also recommend taking the extra step of applying primer to the inside surfaces of the cylinder on the non-bearing surfaces," says Gramzinski.
He adds that PAA coats all exposed surfaces, to include the axle with either permanent or temporary protection from the elements so the gear can be stored for significant periods of time. For instance, the axles are coated with a petroleum-based wax and all the landing gear shipped by PAA are filled with hydraulic fluid and all air is removed from the system.
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