A fresh perspective on why landing gear need an overhaul
By Greg Napert
Thousands of pounds of pressure bearing down thousands of times — hard landings; missed approaches; dirty, dusty runways; 105 degrees F to -60 in 30 minutes; student pilots; overheated brakes. Welcome to the life of a landing gear. You know - those brilliantly engineered devices that, if the rest of the aircraft were made as well, would put aircraft maintenance personnel in the same room as the Maytag repairman.
It's true, landing gear are not very problematic relative to the rest of the aircraft, yet all it takes is one landing gear failure to realize why it is they were engineered the way they are. And contrary to what one might think, a quick breakdown of landing gear at the end of its cycle can give pause to the technician over the need for regularly scheduled care and inspection.
So it is, that AMT magazine travelled to Professional Aircraft Accessories (PAA) in Titusville, FL, to take a close look at a landing gear overhaul facility and the process of reconditioning landing gear — landing gear that have reached the end of its design life.
PAA specializes in the overhaul of Beechcraft 1900 and King Air landing gear. Joseph Gramzinski, Chief Inspector of the landing gear overhaul department for PAA, says the typical overhaul period for Beech 1900 and King Air series of aircraft landing gear is 10,000 cycles or five years, although some airlines that have been allowed to extend that to 12,000 cycles. In reality, however, airlines never make it to five years. They reach the 10,000 or 12,000 cycle limit way before the five-year period — typically within two to three years.
With regularly scheduled overhauls, landing gear can actually be in service for years. In fact, many landing gear in operation are 30-plus years old — a concern for those in the overhaul business.
According to Gramzinski, "One of the things that we are seeing in the shop more frequently as time goes on is severe corrosion — particularly with older magnesium components used in landing gear. Older King Air gear were manufactured with magnesium, which is a lightweight and very strong material." Unfortunately, it's come to light that magnesium has inherent problems that make it unsuitable for landing gear use. The biggest problem being corrosion as a result of dissimilar metals and exposure to elements. A steel bushing inside a magnesium housing or grease fittings, for instance, will all show signs of corrosion around the area where the magnesium and steel are touching — particularly where there is an opportunity for moisture to enter between the two metals."
"I have also seen gears cracked in the corroded area. Beech has since grown wise to the problems related to magnesium and has replaced all magnesium parts with aluminum. Aluminum is adequate in terms of strength, with the advantage of being much more resistant to corrosion."
"It's not very often that we even get a magnesium gear that is re-useable today. Many of them have been in service for many years and it's time to replace them. I would say that four out of 10 magnesium gears are shot and need to be replaced," says Gramzinski. All of the 1900 landing gear are aluminum so they don't present the same kinds of problems. However, 1900 landing gear carry their own set of problems, the major one today being with the 1900D landing gear.
"The problem with the 1900D is that when Beech built the 1900D, a much bigger and heavier aircraft, they used the same gear that was designed originally for the 1900," says Gramzinski. "The result is that 1900D gear exhibit much higher rates of cracks and wear than gear that are used on the 1900."