This publication has been developed by AOPA staff pilots and mechanics in order for pilots to better understand what is permitted under the privileges of preventive maintenance and the obligations that are imposed when performing maintenance. We sincerely hope the information contained in this booklet will be helpful to you and wish you many rewarding hours under the cowling.
The Federal Aviation Regulations spell out in some detail what pilots (who are not certificated airframe and powerplant mechanics or repairmen) may do to maintain their aircraft. These functions fall under the heading of "preventive maintenance" to distinguish them from more complex maintenance,
FAR Part 43, Appendix A, Paragraph C — Preventive Maintenance
Please read carefully the following 32 items that are permitted under the privileges of preventive maintenance and the short brief that follows. They will help you better understand your privileges. Item number 30 pertains to primary category aircraft only. To understand what is required when performing preventive maintenance, you should also read thoroughly AC 43-12A, which follows those 32 items.
Preventive maintenance is limited to the following work, provided it does not involve complex assembly operations:
Removal, installation, and repair of landing gear tires. Tire changes may not be as simple as anticipated; here are some important considerations: Know the proper jacking procedure for your aircraft as outlined in the service manual. The aircraft should be jacked in an enclosed hangar. If the aircraft must be jacked outside, take into consideration wind and proximity to taxiway; Consider how the removal of wheelpants will affect other systems; Know the type of brake system and how it may affect wheel removal and installation; Removal and installation of the wheel-retaining nut requires a special touch. Have your mechanic demonstrate how freely the wheel should rotate after being installed. Replace the old cotter pin with a new one of proper size;
WARNING! Due to high air pressure don't forget to deflate the tire prior to disassembly of the wheel halves for tire and tube replacement. Another important consideration is the proper torque on the bolts securing the wheels halves together.
Replacing elastic shock absorber cords on landing gear. Shock absorber cords, commonly called bungee cords, are found on many types of airplanes. Examples: Cub, Aeronca, and Pitts. At first glance, changing the bungee cords looks like a simple task. Believe us, if you don't have the proper tools, it's like going hunting for a grizzly bear with a hickory stick. Don't do it.
Servicing landing gear shock struts by adding oil, air, or both. The FARs allow the adding of oil and air to air-oil or oleo struts. However, many manufacturers recommend the use of nitrogen instead of air, which helps to prevent the possibility of corrosion. It's also a good idea to keep that dirt and grime removed from the bottom of the shock strut by wiping it down using a clean rag with some MIL-H-5606 on it. This will help to increase the life of the strut.
Servicing landing gear wheel bearings, such as cleaning and greasing. Cleaning and greasing wheel bearings is an art. There are several very important steps to follow when servicing the wheel bearings:
Cleaning — This must be done thoroughly, using a cleaner such as Varsol.
Inspection — Now that the bearing is cleaned, inspect the roller and inner and outer races for deterioration.
Greasing — If you don't have access to a bearing grease machine, get ready to get dirty. Take a nice dab of grease and put it into the palm of your hand. Force the grease into the side of the bearing until the grease comes out the other side. Now you have accomplished the ultimate in preventive maintenance.
Replacing defective safety wiring or cotter keys. Always place safety wire in a manner to cause the item to be tightened. Use approved safety wire of the thickness specified, normally .032 and .041 (refer to service manual for recommended safety wire to be used). Don't over-torque or under-torque nuts or bolts in order to align cotter key holes. Do not use safety wire bought from a hardware store; it's not approved for aircraft use.
Lubrication not requiring disassembly other than removal of nonstructural items such as cover plates, cowlings, and fairings. If you are going to lubricate moving parts on your aircraft, first refer to the lubrication section in the service manual for the type of lubricant and how to apply it. You should also check with your A&P mechanic before getting started. Many Piper aircraft have Teflon-coated aileron hinges and should not be lubricated. Engine oil change is one of the simplest tasks that pilots are allowed to do under the privileges of preventive maintenance, but it's one of the most critical.
Start by checking with your mechanic for any airworthiness directives that apply when changing engine oil in your airplane. One that comes to mind is Avco Lycoming 80-04-03 R2, which requires using an additive in the engine oil and inspection of the oil filter. Only an A&P mechanic can sign this AD off and return the airplane to service.
Many people today are doing oil analyses. One oil analysis will tell you very little about your engine. You will need to develop a history of oil analyses by taking oil samples from the same location and after the same number of hours each time you collect the oil samples. Then you will start to develop a history on what's happening inside the engine.
Another good idea is cutting the oil filter open and rinsing the filter element in a bucket of Varsol or a similar material. Use a magnet to extract ferrous particles, and save them for later examinations. Filter the remaining solvent through a coffee filter, and examine the remains. You should ask your A&P mechanic for advice on what you see the first couple of times. Many people will save the coffee filter and particles until the next engine oil change for comparison.
Making simple fabric patches not requiring rib stitching or the removal of structural parts or control surfaces. In the case of balloons, the making of small fabric repairs to envelopes (as defined in, and in accordance with, the balloon manufacturer's instructions) not requiring load tape repair or replacement. Remember: no rib stitching or control surface repair.
Replenishing hydraulic fluid in the hydraulic reservoir. MIL-H-5606 is the common type of hydraulic fluid used in light airplane brakes and hydraulic gear systems. Use of other than recommended fluid can cause damage to seals, O-rings, and other parts of the system. Be sure you add only the same kind of fluid as that already in the system; follow instructions in the service manual.
Refinishing decorative coating of fuselage, balloon baskets, wing tail group surfaces (excluding balanced control surfaces), fairings, cowlings, landing gear, cabin, or cockpit interior when removal or disassembly of any primary structure or operating system is not required. Refinishing decorative coating: At first glance, this sounds like a simple task, but it becomes complicated very fast. You should start by checking the service manual for recommended procedures and material to be used. Then discuss your intentions with your mechanic and a reputable paint shop attendant. You will need a place to buy those materials and dispose of the unused materials and remains, and they may prove to be excellent sources.
Many aircraft manufacturers require control surfaces to be balanced after painting, so leave those parts to the professionals. Remember: The quality of paint and workmanship will affect not only the value of your airplane, but performance, as well.
Applying preservative or protective material to components where no disassembly of any primary structure or operating system is involved and where such coating is not prohibited or is not contrary to good practices. Check with your mechanic prior to applying preservatives or protective materials to ensure their lasting effect. Some problem areas that have been noted are alternator drive belts and autopilot servo clutches.
Repairing upholstery and decorative furnishings of the cabin, cockpit, or balloon basket interior when the repairing does not require disassembly of any primary structure or operating system or interfere with an operating system or affect the primary structure of the aircraft. When repairing or replacing upholstery, you are required to meet the original type design requirements. Use only material that has met the burn test requirements. The supplier of the aircraft interior will provide you with the needed paper work for your logbook. Do not buy materials from a local upholstery shop because your mechanic may ask you for the certification paperwork at the next annual.
Making small simple repairs to fairings, nonstructural cover plates, cowlings, and small patches and reinforcements not changing the contour so as to interfere with proper air flow. Be careful; what you consider a simple repair may not be. You should refer to the service manual and then ask for advice from your A&P mechanic before making a judgment call. You must use approved material and procedures to do the repair.
Replacing side windows where that work does not interfere with the structure or any operating system such as controls, electrical equipment, etc. Remember that we are talking side windows, not windshield; leave that up to the A&P mechanic. There are many airplanes out there in which replacing a side window is a simple task. However, be careful. As the aircraft systems become more complicated, so will the side window installation.
Replacing safety belts. You are allowed to replace your seat belts and shoulder harnesses with approved belts for your make and model airplane. If you elect to change the belts it is strongly suggested that you follow the service manual instructions for installation. If the manual calls for two washers and a spacer, use them. Changing the belts is definitely a safety-of-flight issue, which may affect your well being.
Replacing seats or seat parts with replacement parts approved for the aircraft, not involving disassembly of any primary structure or operating system. Once again, this should be regarded as a safety-of-flight issue that can affect your well-being. The seats are specifically designed. Don't modify them to make them stronger or more rigid. Replacement seats or seat parts must be of an approved design for your make and model airplane.
Trouble shooting and repairing broken circuits in landing light wiring circuits. This doesn't include position and panel lights or similar lighting systems on your airplane. If you elect to venture into other systems, words of caution: Lack of knowledge of the system may cost you more money for needed repairs.
Replacing bulbs, reflectors, and lenses of position and landing lights. Replacement is allowed in these two systems.
Replacing wheels and skis where no weight and balance computation is involved. Enough said.
Replacing any cowling not requiring removal of the propeller or disconnection of flight controls. Pilots are permitted to remove and replace cowlings and cowl flaps on the aircraft they own or operate. However, don't forget that only certified mechanics may remove a propeller.
Replacing or cleaning spark plugs and setting of spark plug gap clearance. Some important items to consider when changing spark plugs: Have available and use the proper manuals, tools, and equipment needed for the job, which includes a torque wrench. Use the proper spark plugs for the engine. Know the plug rotation sequence for the engine. Many people use a simple process of rotating the plugs from top to bottom and then next in firing order.
Replacing any hose connection except hydraulic connections. Owners are allowed to replace any hose or hose connection except hydraulic connections, which also includes broken lines. You are also allowed to change such lines as:
Cabin air hoses;
Carburetor heat hoses;
Cooling air hoses for radios.
Owners may replace static pressure lines except when used for IFR flight (see FAR 91.411); however, it is strongly suggested that you leave those to the A&P mechanic.
Replacing prefabricated fuel lines. You are allowed to replace prefabricated fuel lines with approved prefabricated fuel lines for your make and model airplane.
Cleaning or replacing fuel and oil strainers or filter elements. Follow the service manual instructions when cleaning or replacing fuel, oil, induction air, and vacuum filter elements. Use only approved strainers and filters when replacing them. The one from the automobile parts store is not approved.
There are several ADs that come to mind when talking about filter changes. You should also check with your mechanic for all ADs that apply to your airplane. AD 84-26-02 requires replacement of the paper induction filter prior to reaching 500 hours time in service. You are allowed to change the filter, but only an A&P can sign off the AD and return the airplane to service. Another AD that comes to mind is Avco Lycoming AD 80-04-03 R2, which requires at the next engine oil change, not to exceed 50 hours, adding an additive to the engine oil, examination of the engine oil suction screen for presence of metal particles, and the inspection of the external full-flow oil filter for metal particles by cutting it open so that the pleated element can be unfolded and examined. You can change the oil and make your entry in the logbook, but once again, only an A&P mechanic can return the airplane to service by signing off the AD.
Replacing and servicing batteries. When replacing your airplane's battery, use only an approved battery for your make and model airplane. You are also permitted to add water (distilled water) and charge your battery. If you need to clean the battery, terminals, or battery box area, baking soda works about the best. Flush with fresh water when you're completed. Don't allow any baking soda to enter the battery.
Emergency Locator Transmitter battery replacement is also permitted, provided you are able to follow the manufacturer's recommendations. Don't forget that the new expiration date for replacing (or recharging) the battery must be legibly marked on the outside of the transmitter and entered in the aircraft maintenance record.
Cleaning of balloon burner pilot and main nozzles in accordance with the balloon manufacturer's instructions. Comply with manufacturer's recommendations.
Replacement or adjustment of nonstructural standard fasteners incidental to operations. You are permitted to remove and replace nonstructural standard fasteners, which also includes the removal and replacement of screws or rivets used to attach fasteners. Remember that you must use the approved fasteners, screws, and rivets for your airplane. If you are one of those mechanically gifted people, have at it: drive those rivets. But if you like to put a square peg in a round hole, this may be a complex task for you. Leave it to the professionals.
The interchange of balloon baskets and burners on envelopes when the basket or burner is designated as interchangeable in the balloon type certificate data and the baskets and burners are specifically designed for quick removal and installation. You must comply with type certificate data sheet.
The installations of anti-misfueling devices to reduce the diameter of fuel tank filler openings provided the specific device has been made a part of the aircraft type certificate data by the aircraft manufacturer, the aircraft manufacturer has provided FAA-approved instructions for installation of the specific device, and installation does not involve the disassembly of the existing tank filler opening. Always comply with the FAA-approved instructions from the manufacturer when installing anti-misfueling devices on your airplane.
Removing, checking, and replacing magnetic chip detectors. Comply with the engine and airframe manufacturers' recommendations when removing, checking, and replacing the magnetic chip detector.
The inspection and maintenance tasks prescribed and specifically identified as preventive maintenance in a primary category aircraft type certificate or supplemental type certificate holder's approved special inspection and preventive maintenance program when accomplished on a primary category aircraft provided:
They are performed by the holder of at least a private pilot certificate issued under part 61 who is the registered owner (including co-owners) of the affected aircraft and who holds a certificate of competency for the affected aircraft (1) issued by a school approved under 147.21(e) of this chapter; (2) issued by the holder of the production certificate for that primary category aircraft that has a special training program approved under 21.24 of this subchapter; or (3) issued by another entity that has a course approved by the Administrator; and
The inspections and maintenance tasks are performed in accordance with instructions contained by the special inspection and preventive maintenance program approved as part of the aircraft's type design or supplemental type design.
Removing and replacing self-contained, front instrument panel-mounted navigation and communication devices that employ tray-mounted connectors that connect the unit when the unit is installed into the instrument panel, (excluding automatic flight control systems, transponders, and microwave frequency distance measuring equipment (DME). The approved unit must be designed to be readily and repeatedly removed and replaced, and pertinent instructions must be provided. Prior to the unit's intended use, an operational check must be performed in accordance with the applicable sections of part 91.
Updating self-contained, front instrument panel-mounted Air Traffic Control (ATC) navigational software data bases (excluding those of automatic flight control systems, transponders, and microwave frequency distance measuring equipment (DME)) provided no disassembly of the unit is required and pertinent instructions are provided. Prior to the unit's intended use, an operational check must be performed in accordance with applicable sections of part 91.