Airframe and Powerplant

Smooth Moves: Oils, Greases, and Lubes

October 1, 2000

An ounce of lubrication is worth a pound of maintenance

It's time to add another skill to washing and polishing your airplane. If you are already involved in oil changes, taking and sending oil analyses, and cutting open oil filters, then you're ready to further expand your aviation preventative maintenance skills in the lubrication arena. If greasing and changing your airplane's oil are not tasks you're interested in, there are still little lube jobs that can be done to improve the operation of your airplane. For instance, a few minutes spent spraying some lubrication on a balky defroster control cable should pay off during your next night landing in the rain.

Now is also the time to start preparing for winter flying. Completing the tasks described in this article can result in better operation of the airplane systems and reduced costs during maintenance. To paraphrase an old saw, an ounce of lubrication prevention is worth a pound of maintenance-cost cure.

Nothing takes the place of proper lubrication—every moving part needs lubrication in some form to operate as designed. Even rubber door seals benefit from regular lubrication.

Everyone knows that an airplane's expensive engine will be better disposed to provide trouble-free, dependable service if the oil and filter are changed at regular intervals and the engine is flown often. The reason for this is simple—operating the engine lubricates the internal parts; this prevents metal-to-metal contact, and the resultant coating of oil prevents rust within the engine. The same cause-and-effect relationship is true for every other moving part on your airplane. Learning the location of and lubricating the many hinges, pivot points, elbows, and actuating rod ball ends on the airframe of your airplane is a relatively easy task that yields tangible long-term benefits.

Lubrication is so vital to the airworthiness of an airplane that airframe manufacturers specify in their maintenance manuals exactly which type of lubrication should be used, where it should be used, and how often it should be applied.

Preventative maintenance

Airplane owners are permitted to do most of the lubrication tasks on their airplanes. Appendix A of FAR Part 43 is titled Preventative Maintenance. According to this regulation, an owner may perform the tasks outlined in this appendix without oversight by a licensed mechanic. This appendix details the extent of owner-performed preventative maintenance lubrication tasks by allowing "lubrication not requiring disassembly other than removal of nonstructural items such as cover plates, cowling, and fairings." In addition, there's a preventative task list approving "servicing of landing gear wheel bearings, such as cleaning and greasing." The challenge for the owner willing to take on the lubrication of his airplane is twofold: Where can the manufacturer's maintenance manuals be obtained, and what tools and supplies does he need?

Service manuals

Airframe and engine manufacturers sell maintenance manuals. You can buy your own copy of the manual, or you can talk your maintenance facility into letting you copy the section of the manual that addresses servicing. But there's a caveat. Service manuals were improved greatly starting in the mid- to late 1970s—if the copy of the service manual that covers your airplane does not seem to go into much detail about lubrication, try to obtain a copy of the servicing chapter from a more recent manual for your model. For instance, Cessna printed a service manual for the 100-series of airplanes. This manual covered every 100 series airplane built from 1958 through 1962—the 150, 172, 180, 182, and 185. Admittedly, the lubrication of these simple airframes is straightforward, but later manuals go into more detail. More recent manuals also list the latest lubrication specification numbers. As the industry matured and airplanes became more sophisticated and complex, the manuals grew thicker and, of necessity, were narrowed in focus.

Mooney issued one service manual covering its M20-series airplanes from 1968 to 1984—the M20C, M20D, M20E, M20F, M20G, and M20J (201) models. This manual is more than half an inch thick. The service manual for the M20K, also known as the 231, is an inch thicker. The service manual format throughout general aviation changed in the mid-1970s as manufacturers agreed to adopt a universal General Aviation Manufacturers Association (GAMA) manual format.

There is a catch, though, even with the GAMA-format manuals. Unfortunately, many general aviation maintenance manuals are very vague about the exact points that require lubrication. The Mooney 231 manual is a good example of this—the main landing gear grease fittings lubrication guide says only that Mil-G-81322 grease should be used at 100-hour intervals. As in many other general aviation service manuals, determining the number of lubrication points and locating all of them is left to the person doing the lubrication.

Maintenance must be done by the manual

Each owner who undertakes the responsibility for ensuring that his airplane is lubed correctly must have the appropriate section of the aircraft service manual—it's illegal to perform maintenance without the appropriate manuals. The servicing chapter of each manual specifies the system to be lubed, the type of lubricant needed, and the frequency of lubrication. If the frequency chart shows that 100 hours is the desired interval, this means at every 100 hours flown, or at each annual.

Maintenance record entries

All maintenance done on an airplane is required to be signed off in the aircraft records— even if the pilot is doing preventative maintenance. According to FAR 43.5, a maintenance record entry must be made following preventative maintenance. FAR 43. 9 (a) (1 through 4) requires that the entry contain a description (or reference to data acceptable to the administrator) of work performed; the date it was completed; the name of the person performing the work; and the signature, certificate number, and kind of certificate held by the person. The signature constitutes the approval for return to service only for the work performed.

A sample maintenance record entry would be a legal entry if it read: "January 1, 2000. Lubed landing gear in accordance with (usually abbreviated and written as I/A/W) Mooney M20K service manual, paragraph 5-20-07. Joe Pilot, Private Pilot 555-55-5555," followed by Joe Pilot's signature. You'll notice that there isn't a requirement for aircraft time or tach time, but most entries include this important information.

Logbook or maintenance records?

It's also important to note that there is no requirement to keep the maintenance records in a logbook, although most people assume that a logbook is required. It would be perfectly legal to create a lubrication log for your airplane and enter the lubrication signoffs in that book, as long as the book is included with the other maintenance records. Many pilots are a little leery about signing their name in the aircraft logbook, but they're in violation of the FARs if work is performed and not signed off. Remember that the FARs say that the signature required constitutes the approval for return to service only for the work performed.

Recordkeeping is simple and important, but proper servicing is critical. If you, as an owner doing preventative maintenance, ever have a question about procedures, stop and ask an experienced mechanic. And get your work inspected if the task has a bearing on safety. Cleaning and lubing wheel bearings is admirable and necessary, but if you leave out an axle nut cotter pin, the few minutes it takes to get someone to inspect your work will seem like small potatoes compared to the possible cost of wheel and axle damage.

Do it once with the experts

The best way to learn some of the tricks of lubrication is to ask your maintenance shop if you can try your hand at the lubrication procedures during an annual inspection. I'd venture a guess that at least 90 percent of the mechanics in general aviation will welcome such a proposal with open arms. There are three reasons for this. Mechanics would rather be performing the technical tasks that they trained for. There's simply more gratification in troubleshooting and repairing a system than there is in greasing a wheel bearing or landing gear. Also, mechanics like owners who are involved with their airplanes. Finally, there will be some questions that arise as you attempt to lube the airframe. It's very helpful to have an experienced mechanic nearby who can answer your questions before frustration sets in. Pick one who has the experience to explain tricks, such as the fact that the best time to lubricate landing gear grease fittings is when the airplane is on jacks and the aircraft weight is off the pivot points. Make learning lube tricks easy on yourself—take advantage of the local lube guru.


In addition to the printed information from the service manual, you're going to need a good grease gun. There are two general types—lever powered and air powered. It's my experience that most greasing on general aviation aircraft is done with a manually powered gun because of its simplicity, and the fact that there aren't often enough grease fittings to justify the cost of an air-powered gun. Both guns are capable of applying amazing amounts of pressure, with 6,000 to 10,000 psi being the norm. A flexible hose between the grease gun and the adapter will make access to the grease fittings much easier.

Remember that regular greasing does two things—it ensures that wear between moving surfaces is kept to a minimum by lessening friction, and it keeps the lubrication in the joint clean. Lubrication is good, but regular lubrication with the proper grease is the key.

Types of grease

There are many different types of grease. Bendix sells a special grease for Bendix magneto bearings, and there's special grease specified by Bell Helicopters for splined joints. In short, there are a few special lubricants required on almost every airplane. In general, though, one grease covers almost all of the greasing tasks owners are allowed to do.

According to aircraft service manuals, the general lubrication grease for joints in Cessna piston singles and twins, and Mooney singles, is the same grease—Mil-G-23827. This code is a military specification for aircraft and instrument, gear and actuator screw grease. The following greases, among others, comply with this specification: Aeroshell 7, Chevron Aviation grease 55, Braycote 6275, and Royco 27. All of these greases have excellent corrosion resistance, work well in medium-load applications, and exhibit stability from minus 100 to 250 degrees Fahrenheit.

One grease fits all

Wheel-bearing lubrication requires grease that can perform under high pressures, has good adhesion properties, and will remain serviceable while providing lubrication and bearing corrosion protection during extremes in air temperatures. The mil spec number for wheel-bearing grease is Mil-G-81322. Sharp readers may note that this is the grease Mooney specifies for the landing gear grease fittings on its airplanes. In other words, this grease can be used for all grease tasks on your airplane.

The description of this grease is wide temperature range grease. Royko 22C, Aeroshell 22, and Mobile 28 all fit this specification.

Wheel bearings

Most mechanics will agree that aircraft wheel bearings are the most overserviced parts on general aviation airplanes. Cessna recommends lubing wheel bearings every 400 hours if the airplane is not operated in extremely dusty or wet conditions; the 1960 Cessna 210 service manual lists 500 hours as the bearing lube interval. Mooney's M20K manual suggests 250 hours as a proper interval for normal operating conditions. Most maintenance experts will want to assure that the bearings are lubed correctly within 100 hours after taking possession of a new plane; after the initial inspection and greasing, the interval can be increased depending upon the operating environment. There's no need to grease the wheel bearings at every annual unless operations have been conducted in unusually dusty or wet conditions.

Rainy day lubrication

While changing engine oil, greasing fittings, and lubing wheel bearings are the big three of lubrication, there are many small simple tasks that will make your airplane systems operate easily.

All piano hinges, usually used on oil filler doors, cowling inspection panels, trim tabs, fuel strainer doors, cabin door hinges, landing gear doors, and cowl flap hinges, benefit from a regular dose of spray lube. The latest Cessna single-engine service manuals specify Mil-L-7870, which is the spec number for general purpose oil. It's pretty rare to actually see anyone using an oil can to lube these hinges nowadays—most lube tasks specifying oil are now accomplished with spray lubes. The Mooney manuals specify Tri-Flow, a Teflon spray, for lubrication tasks that traditionally required oil. Spray lubes seen around general aviation shops include LPS-1 and 2, CRC 3-36, and Tri-Flow. Regular applications of these easy-to-apply lubes will pay off.

One other lube that comes in handy and is mentioned in the Mooney manuals is Door Ease, a push-tube of stick lubricant that is used to lube door strikers and catches. Lubed door strikers lessen the need to slam the doors, which makes for less skittish passengers.

All of these tasks improve the operation of expensive airplane systems. Pilots and passengers all benefit when the airplane in which they're flying in is well-maintained. Lubrication is maintenance.

Links to additional information about aircraft lubrication may be found on AOPA Online ( E-mail the author at [email protected].