TRENDS

Landing Gear and the Mechanic: a Proper Groundingby Daniel Brindley

MRO technician repairing the brake mechanism within airplane landing gear.

Airplane landing gear may seem like a simple matter, but it’s more complex than even many mechanics realize.

Many mechanics (and certainly the flying public) mistakenly assume that landing gear is among the most basic and sturdiest aspect of the aircraft. It’s true; landing gear are built to be tough, but they’re susceptible to a myriad of insidious problems, including corrosion, stress, contamination, and pilot misuse.

If landing gear aren’t properly maintained, the operational lifespan as specified by manufacturers isn’t reached, resulting in increased MRO costs, if not outright replacement.

“Airplane landing gear are often given short shrift by mechanics, because they assume they’re basic,” says Paul Lombino, aviation analyst based in Boston. “But they’re more fragile and vulnerable to malfunction than you’d think.”

According to Lufthansa Technik, mechanics should follow a list of “best practices” to care for aircraft landing gear and landing gear parts.

German-based Lufthansa Technik has partnered with American-owned landing gear overhaul organization Hawker Pacific Aerospace and further extended its MRO activities in North America. Here’s what the combined entity recommends.

MRO Best Practices for Landing Gear

1) Protect landing gear from foreign object damage.

Aircraft landing gear must withstand enormous stresses and strains. At all times, the gear’s pressurized oleo-pneumatic shock-absorbers exert stress on their metal housings. The sheer impact of hitting the tarmac over and over again stresses the entire system, no matter how precise the landing. Not just vertical but also horizontal forces come into play, such as when the aircraft brakes during landing or accelerates during takeoff.

But it’s not just operational. When an aircraft is towed, it puts stress on the forward landing gear. The tarmac also is a landmine of FOD (foreign object damage) risks, including debris, parts and tools that can collide with airplane landing gear, sometimes cracking, bending or denting landing gear parts. Sloppy jacking and towing are factors, too.

2) Beware of hydrogen embrittlement.

Many mechanics will pressure wash aircraft landing gear and assume that just because it’s spotless and shiny, it’s okay. But hidden problems could be festering.

Washing can cause water to seep into bushings and joints, causing corrosion. Some solvents, such as paint stripper, can cause what’s called “hydrogen embrittlement” in landing gear.

This occurs when hydride-forming metals such as titanium, vanadium, zirconium, tantalum, and niobium become brittle and fracture due to the introduction and subsequent diffusion of hydrogen (via water) into the metal.

Lombino says the only way to counteract hydrogen embrittlement is to remove the affected landing gear parts and bake them in a special oven at 375 F for 23 hours. This enables the hydrogen atoms to migrate to the surface and then escape.

3) Proper lubrication.

Insufficient lubrication is a common mistake in MRO shops, generating needless deterioration in many landing gear parts.

Proper lubrication reduces friction and stress and facilitates the proper transfer of forces throughout the aircraft landing gear during use. Lubrication is key to keeping out water, de-icing fluid, and other foreign substances that exacerbate corrosion.

Before lubrication, mechanics should check the aircraft’s manual to determine which lubricants and ancillary materials are authorized by the manufacturer for use. The wrong grease can cause damage to landing gear parts.

4) Protect against corrosive agents.

Paint strippers, stringent cleansers, and other corrosive agents are the enemies of airplane landing gear. Hydrogen and the high tensile steel used in the landing gear simply don’t mix well.

Landing gear can become brittle and crack if acids are allowed into the casing. Cracks are costly to fix; if they’re bad enough, the entire apparatus must be replaced. In a worst case scenario, the airplane landing gear will fail during use. And no one wants that.

5) Prevent non-operational impacts.

Pressurized shock-absorbing struts are vulnerable to damage on the tarmac. During an aircraft’s towing and storage, they can get dented, bent, dinged, and nicked. These impacts usually occur during careless handling of the aircraft. When they occur, the shape of the struts can change, resulting in greater stress on landing gear parts.

If any of the above problems occur, it’s crucial for the mechanic to thoroughly document the incident, with pictures of the actual visual damage. Replace the affected part or component and send it out for testing and repair.

Daniel Brindley - Founder CEO and Editorial Director

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