Take a look at the wheel bearing in Figure 1 (below) – it’s dry as a bone – there’s not a speck of grease or lubrication to be found. It looks like it sat in a solvent tank for a month, then tossed on a junk pile. The crazy thing is this wheel bearing came off a King Air during a Phase inspection in my shop years ago.
Back in the day, I had maintained this particular King Air for six or seven years when this happened. It flew about 100 hours per year and was on an annual schedule of two phases per year to ensure all four phases were completed every 24 months as stipulated in the maintenance manual.
This particular maintenance visit was for two phases, a handful of calendar items coming due, and a few customer squawks. It was looking like a very routine visit until my crew tried to remove the wheels in order to grease the bearings (as happens at every phase). They found the wheel bearings on the main gear were drier than dust. They were practically fused to the axles! My crew had to beat the wheels with a mallet to jog them loose enough for removal.
I was in disbelief. The previous year we had performed the six-year landing gear inspections. The wheel bearings were lubed properly at that time – no question about that. The aircraft flew about 100 hours since the gear was done; there was no reason for those bearings to be utterly devoid of lubrication. They were so dry they were about to seize up. Thank goodness that didn’t happen because they would have scored the axles. I don’t want to think about the repairs necessary to remedy that situation!
The Mystery Unfolds …
I couldn’t imagine how this happened. The pilot of this King Air was a no-nonsense, by-the-book type of guy. Conscientious to a fault, he never let any detail escape his attention. Prior to coming to my shop, he’d had some bad experiences with maintenance. As a result, he was very cautious about where he took the King Air for service. He happily flew from Denver to Southern Nevada for Phase inspections. If he got stuck somewhere, he wouldn’t have anything done without consulting me first. So, I was mystified as to how those bearings dried out so fast.
The owner of this aircraft was in the pipeline business and owned a lot of equipment. He was meticulous about the maintenance and appearance of all his equipment, including his King Air. Accordingly, his diligent pilot made darn sure that King Air was in pristine condition at all times.
It turns out the pilot happened upon a new, fantastic degreaser. It was perfect for getting grease off everything, and he used it on the King Air to great success or so he thought. This happened right after the gear inspections were done, so of course the landing gear got regular treatment. Liberally applied on a repeated basis, this degreaser worked its way into the wheel bearings and stripped them of all lubrication. You can see the result in the photo. The pilot’s perfect find wasn’t so perfect after all.
What to Use?
All maintenance manuals must identify the greases to be used on an aircraft. There are a few places on a King Air where very specialized greases are specified in the manual. The oxygen shut-off valve is one example. In this article I’m talking about general lubrication items and the manual calls out various mil spec (military specification) greases to be used for these applications.
For wheel bearings, I always favored a wonderfully thick grease that is red in color. Many shops use a yellow grease, but I just loved this red stuff for wheel bearings. I like its consistency and resilience, and it conforms with maintenance manual specs. This is the grease my shop used for the wheel bearings at every six-year gear inspection. Although the wheels and gear are on the 200-hour lube item list, I greased them at every Phase, even if the airplane only flew 40 hours since its last inspection. You can’t grease something too much, but you sure can fail to not grease it enough, and the consequences of doing so are never cheap.
A Fine Mess
I took a lot of flak from my customers about the mess created by my red grease in the months following a Phase inspection. Traces of this grease would appear on the gear after every flight. But no matter how much they complained, I knew darn well they’d rather wipe up a little mess than risk major damage due to insufficient or no lubrication. Now that would be a real mess!
The right grease, properly applied, minimizes friction and promotes longevity of the parts involved. Furthermore, proper lubrication offers protection against corrosion. I cannot emphasize this strongly enough. So, keep a rag handy for those little messes.
Clean Freaks Restrain Yourselves
The maintenance manual specifies that the grease used on your aircraft be water resistant. Obviously, you need something that will survive the rain and routine washing of the aircraft. As most of you know by now, I do not recommend pressure washers in the cleaning of aircraft. If one is used on your King Air, you should personally ensure it is used sparingly.
Never use a pressure washer to clean the wheels or landing gear. Doing so just hastens corrosion, and that equals big, big maintenance bills. Unfortunately, the wheels and gear are exactly where people want to use a pressure washer the most, to remove brake dust in the wheels and grime in the gear. Pilots and owners need to think past a little grease and grime to the cost of exchange wheels after your cores are condemned for corrosion.
If you are an obsessive clean freak – restrain yourself. That is an order! Pressure washers push the grease aside and inject water where it doesn’t belong. Solvents or degreasing cleaners are even worse as they dissolve the grease entirely. When water gets where it should not go, corrosion follows. Please, I am begging you … leave the grease to do its job.
If a mobile detail operation is cleaning your King Air, you must make absolutely certain they do not use a pressure washer on the gear. This is easier said than done. It’s the dirtiest area and they think they won’t get your continued business unless they make your aircraft look ready for the showroom floor. If you can’t be there to supervise their work, consider getting it in writing: “No pressure washing the landing gear.”
Lubrication Schedules
The maintenance manual has very specific directions on what to lube and when. There are lists of things to be lubed every 200 hours, every 400 hours, also every 600, 800 and 1,200 hours. I’m not going to regurgitate the maintenance manual here, but there are a lot of moving parts that need to be greased regularly.
Here’s a short list:
Flaps – flap tracks, flap actuators and flap gear box
Ailerons – trim tab hinge and aileron quadrant
Cable seal – elevator, rudder and aileron
Rudder pedal attach points
Down lock hooks
The lube item checklists are thorough and sometimes repetitive. But again, you can’t over-lubricate something. These checklists are a vital part of your King Air maintenance.
Lubrication may seem boringly basic, but it’s absolutely essential in the maintenance and preservation of your King Air. I ran a version of this article 10 years ago in this magazine. At the time, I wondered if it was too simple of a subject since lubrication is so elementary. On the other hand, lubrication is so consequential to the proper function of any airplane, it makes me think I should mention it in every issue.
Anyone that has ever worked with me knew not to skimp on any lube item. If my customers didn’t hassle me after inspections about red grease splatter, then I didn’t do my job. Your job (and you should choose to accept it) is to kick the pressure washer and the degreaser to the curb and adopt a new slogan: Grease is Good!