Airframe and Powerplant

Preventive Maintenance Primer

October 1, 2001

All it takes is a little gumption and a willingness to learn

Everyone likes to save a few bucks. So it's good news that every certificated pilot can legally carry out certain preventive maintenance chores on their airplane. These chores — which include tasks such as touch-up painting, changing tires, servicing shock struts, and even making simple repairs to fairings and cowlings — help owners learn about their airplanes, and can eventually help move a few maintenance bucks over to the flying budget.

Pilots who undertake these preventive maintenance tasks soon understand their airplanes better, become more competent and comfortable during preflight inspections, and can occasionally use their preventive maintenance skills to perform simple repairs while away from home.

During systems and procedures courses for the Cessna Pilots Association, a staff member would uncowl the engine of a class member's airplane and point out the component parts and accessories such as the magnetos, the prop governor, and the primer system. Most of the attendees would hover nearby, striving to learn more. This seemed to indicate that if guidance is available, most owners are very interested in the inner workings of their airplanes. Along with owner-assisted annual inspections, preventive maintenance (PM) is one of the best ways airplane owners can expand their knowledge base about their airplanes.

Maintenance is serious business

Before we get started, it's important to realize that aviation maintenance is a disciplined activity. The basic maintenance skills used when working on airplanes are not vastly different from those used when working on other mechanical devices. However, these skills must be tempered with the proper mindset and attitude. Owners working on their airplanes must always be willing to stop what they're doing and consult a manual, or a certified technician, when they're not absolutely sure of the procedures and specifications relative to the job at hand. "Winging it" has no place in owner-performed preventive maintenance.

For example, when tightening an airplane oil filter during an oil and filter change (which is an approved PM task), the automotive technique of tightening the filter three-quarters of a turn after the gasket contacts the flange is not good enough. Aircraft filters are tightened to a specific torque using a torque wrench. In the case of Champion oil filters, a recommended lubricating paste (Dow Corning DC-4) should be sparingly applied to the gasket before the filter is tightened to 16 to 18 foot-pounds.

Inspections and checklists

The other big difference between aviation and most other mechanical undertakings is that aviation maintenance safety is reinforced by an inspection system. Individuals carrying out preventive maintenance on their personal airplanes must develop some sort of inspection plan.

Ideally, you should ask your local A&P mechanic to inspect your work. But if this doesn't work out, and there's no other person nearby who is competent to inspect the task you've completed, taking time to verbally review what you've done to another person — even the local security guard or adjacent hangar tenant — is better than nothing.

As seen in this NTSB accident report, even experienced professionals should utilize an inspection system. The pilot was beginning the first postmaintenance check flight after rebuilding the airplane. As the airplane began to fly off the runway, the pilot pulled aft on the yoke, and the airplane nosed over. Postaccident inspection revealed that the elevator cables were connected backwards. The pilot, who is also a certificated aircraft mechanic, told the NTSB investigator in charge that he bought the airplane as a project and rebuilt it. He stated he hooked up the elevator cables backwards, and did not recognize the error during his inspection. He added that he did not have anyone else inspect his work.

What can I do?

There are 32 tasks that an owner can perform legally on a fixed-wing airplane. These tasks are listed in Appendix A to Federal Aviation Regulation Part 43.

AOPA's Aviation Services department has written a booklet titled A Pilot's Guide to Preventive Maintenance ( www.aopa.org/members/files/guides/prevmain.html). This booklet describes the tasks that can be undertaken by a certificated pilot on any aircraft owned or operated by that pilot.

Getting started

Let's say that the nose tire of your airplane looks pretty crummy — there is a lot of cracking and the tire looks extremely weathered. You check the logbook and determine that the tire hasn't been changed for six years. You go to the list of preventive maintenance tasks and see that removing, installing, and repairing landing gear tires is an approved task. What next? Get some instruction. Schedule a few hours when you can hang out down at the airport and work with your mechanic as he leads you through the process of changing a tire. You should take notes, ask questions, and even take pictures in your effort to learn. Upon completion of this instruction, are you then approved to perform this task on your own in the future? Well, yes and no.

Manuals are required

When an owner takes on the responsibility of performing preventive maintenance tasks, he (or she) is bound by some of the same regulations as a certificated A&P.

FAR 43.13(a) says that anyone performing maintenance is required to use "methods, techniques, and practices prescribed in current manufacturer's maintenance manuals." That doesn't mean that you have to go out and buy each manual — your mechanic may allow you to copy the pertinent sections out of his manuals. If you are a member of a type club, it may be able to send you the pages you need.

To be on the safe side, and comply with the letter of the law, it's a good idea to see if the manufacturer has issued any service bulletins, service letters, or notices related to the task at hand. Although it's not required, it's an excellent idea to create a checklist for each task and work down the list, checking off each item as it's finished.

A checklist for tires

A checklist for a nose-tire change on a single-engine Cessna may begin something like this: Chock main tires; jack up the nose of the airplane sufficiently to raise the nose tire off the ground; deflate the tire; remove the axle throughbolt cotter pin; remove the axle throughbolt nut and push out the throughbolt; remove left and right axle spacer support cups; slide nose tire wheel and axle spacers from between nosewheel fork; put spacers aside; remove left (side) wheel bearing snap ring, the two grease seal rings, the grease seal felt, and the bearing from the wheel half.

The, identify the left (side) wheel parts and left side of wheel; do the same for the right (side) wheel bearing parts; break tire beads from wheel halves; remove wheel nuts and throughbolts and split the wheel.

We're going to stop here, but you get the idea. A checklist can be as definitive as this one, or it can list only the critical operations. The scope of the list depends on the experience level of the person doing the work.

Notice that there's an item in the checklist to identify the left (and right) side bearings and wheel halves. It's important that the left bearing (these tapered roller bearings are actually termed cones) goes back in the left bearing race (cups) and the right bearing goes back in the right bearing race — these parts wear together during normal usage and mixing them up will shorten bearing life.

This little tidbit of bearing knowledge isn't written in any airplane service manual that I know of — it's just one of those tips that is learned with time. Details like this are why it's important to get a checkout from your mechanic before any of the preventive maintenance tasks are undertaken.

Logbook entries

Owners doing preventive maintenance are required to return the aircraft to service by making an entry in the aircraft records. FAR 43.9 spells out what is required in this entry.

The entry must contain a description of the work performed, the date of completion of that work, and the signature and certificate number of the person who performed the work. Pilots use their pilot certificate number when making these entries. Examples are given in the AOPA handbook mentioned earlier.

At this point, some owners may say that all the requirements for preventive maintenance take the fun out of it. It may look that way, but what the FAA is really saying is that any aircraft maintenance task worth doing is worth doing right. The owner has certain privileges, but also has to recognize that with the privileges come some responsibilities.

As with the medical profession, the first rule of any owner-performed maintenance is to do no harm. It takes years to learn all the tricks and techniques involved in performing safe aircraft maintenance. The most gratifying way to learn these skills is to start doing them.

Advantages of preventive maintenance

Let's say that you've taken the time to learn how to remove, clean, gap, and reinstall your spark plugs. This is one PM task that can save money and time if you're ever caught away from home with a fouled spark plug. If you've planned ahead, you've put together a small tool kit containing (at least) one spare spark plug, a small bottle of antiseize compound, the proper-size wrench for the high-tension spark plug wire nuts, and a ratchet and socket that fits the spark plug, and stashed it all in your airplane baggage compartment.

If you subsequently encounter a fouled spark plug that won't burn clean during your pretakeoff runup, it's not such a big deal to determine which plug is fouled and change it. This little freedom comes because you've taken the time to learn about spark plug PM.

The fouled-plug test

You say you don't know how to determine which spark plug is fouled? Simple. After taxiing back from the run-up area with a rough or out-of-limits mag drop, find a safe place to park and shut down the engine. Remove enough cowling (it's allowed under PM), or open the cowling to the extent that the exhaust pipes are accessible.

After the engine has cooled off for 15 minutes, run the engine at 1,000 to 1,200 rpm on the bad magneto (the one with the excessive drop) for one and a half minutes. Then shut down the engine with the mixture and determine which exhaust pipe is cold. Most mechanics I know just dip their finger in water and then quickly touch each exhaust pipe in succession. It will be obvious which cylinder isn't firing.

By following the spark plug wires from the cold cylinder back to the magneto that was providing ignition to the engine (remember that when the mag switch is on L, you're testing [using] the left mag, and vice versa) you'll be able to determine whether the fouled plug is the top or bottom plug. Change the plug, install the plug lead, reinstall the cowl, perform a preflight test, and if the mag drop is gone, you're on your way.

This is all perfectly legal as long as you create an entry for the maintenance records detailing your efforts before you take off. No, you don't need to have the maintenance logbooks to do this. If you create a record of the PM task you did in accordance with FAR 43.9, you may enter it into the logbook at a later date.

Helpful tools

Although there seems to be a video for learning pilot skills of every stripe, there is a real shortage of home study aids for those interested in preventive maintenance. Recently, Approach Aviation ( www.approachaviation.com) has introduced Preventative Maintenance, the first videotape in its Educated Owner series. This tape, which retails for $34.95, covers legal owner maintenance, owner inspections, oil, oil and filter changes, landing lights, spark plug maintenance, and tire and wheel servicing. I'd recommend it for anyone wanting to get started doing PM tasks.

Federal aviation regulations pertaining to owner-performed maintenance can be found on the AOPA Web site ( www.aopa.org/members/files/fars/far-43.html).

A copy of Advisory Circular 43-13-1B/2A titled, Acceptable Methods, Techniques and Practices of Aircraft Inspection, Repair and Alterations is invaluable to anyone involved in airplane maintenance. This advisory circular, which is more than 300 pages long, along with manufacturers' manuals and other manufacturers' data, forms the cornerstone of every mechanic's library. Reprints of this AC can be purchased for less than $20 at most aviation bookstores.

A little gumption, a checklist for each task, pertinent up-to-date pages of maintenance data for the task at hand, some help from a local mechanic to get you started, a few basic hand tools, and a willingness to learn are all it takes to get started doing your own preventive maintenance.

A few of the payoffs you'll receive are a better technical understanding of your airplane, more confidence in your ability to evaluate your airplane's airworthiness, and the ability to effect minor repairs. All this and some savings on your maintenance budget makes learning preventive maintenance a worthy undertaking.


E-mail the author at steve.ells@aopa.org.