DIY Maintenance: Tools, Manuals, Smarts

Doing preventive maintenance chores yourself can save money and build confidence, but consider working with a shop or mechanic as a backstop.

For some, the fun part of owning an aircraft is the time spent alone with it in the hangar. That eventually leads to wrenching it.

Before you get too deep in the cowling, you should evaluate your technical skills, understand the regulations and inventory the proper tooling. In this article, I’ll outline the regulations and some of the maintenance items the FAA allows you to perform on your certified aircraft (for more freedom, consider an experimental, plus an A&P rating).

Got Tools?

In the 1980s movie Fast Times at Ridgemont High, Sean Penn’s character Jeff Spicoli proclaimed that since his father has an awesome set of tools, he could fix anything. And while you may posses many of those same tools in your T-hangar, the FAA doesn’t quite see it that way when it comes to aircraft maintenance.

Aside from prescribing the maintenance items it considers to be minor and preventive in nature, plus allowing the replacement of parts that don’t require complex disassembly, FAR 43.13 also requires the use of specialized tools and test equipment. How do you find out which tools you need? An FAA-approved maintenance manual is the best source. I think it’s foolish to tackle many of the tasks allowed without having an appropriate manual available for reference. On the shop level, if you don’t have the manual or tools, you aren’t approved to work on it. And even if you have the tools, consider that torque wrenches, meters and tensiometers, to name a few, generally require outside calibration. If you have access to service manuals and literature, they should be the latest revision and applicable to the aircraft you’re working on.

FAR 43.13 uses interesting language when it comes to the quality of your work, basically saying you can’t worsen the condition and consider it to be airworthy. That closes the door to unapproved major modifications or any alterations that deviate from a type design or original parts specification. That will have to be signed off as a major modification on an FAA 337 form, and only repair stations and IAs can approve them.

FAR 43.3 section (g) says the same rules apply to holders of sport pilot certificates when working on LSAs.

Can’t Touch That

The gentle side of the FAA actually promotes owner-performed preventive maintenance—to save money and increase safety—in its AC 20-106 advisory circular and posts a document on its websiteMaintenance Aspects of Owning Your Own Aircraft. It covers best maintenance practices, while referencing the FARs as the final ruling. Remember, advisory circulars are advisory in nature, not must-do regulation.

As for rules, the FAA uses specific language in part 43.3 when allowing for minor and preventive maintenance. For starters, those not holding a mechanic certificate, a repairman certificate or operating under an FAA repair station can’t perform alterations or rebuilding. But you can perform preventive maintenance tasks and the list is extensive. The chart on page 22 is only part of what’s allowed.

To perform the tasks (and to sign it off in the aircraft maintenance records), the FAA says you need to posses a valid Part 61-issued pilot certificate and may only perform preventive maintenance on an aircraft owned or operated by you—the certificate holder with the ID number you’ll record in the logs as proof.

It can be argued that you can’t wrench your friend’s aircraft if you aren’t an owner or operator. Additionally, want to moonlight and perform preventive maintenance at the local airfield on aircraft you don’t own or fly? I wouldn’t do that.

Teaming with a mechanic offers more leverage. For repair actions not considered preventive, FAR 43 says in part that a person working under the supervision of a mechanic or repairman certificate holder may perform the maintenance, preventive maintenance and alteration that his supervisor is authorized perform. The caveat here is the repairman or mechanic has to personally observe you doing the work and be readily available for consultation. This is otherwise known as owner-assisted inspections. Smaller shops may allow it, but larger ones likely will not.

Of course, non-mechanics are not authorized to approve work accomplished by others. That means if your buddy changes your tire while you aren’t present, you can’t legally sign off the task in the maintenance logbook, and neither can he.

How Minor is Minor?

Let’s look at some of the tasks the FAA says are fair game for a non-mechanic to accomplish, understanding that you still might not be competent to complete the task to the standard the maintenance manual prescribes. I’ll start with oil changes.

Just like changing the oil on your vehicle, you’ll get dirty changing your aircraft oil and filter, but that’s where the similarities end.

Depending on the aircraft, you might have to remove and reinstall the cowling to gain access to the drain plug and oil filter. While this isn’t difficult work, you might be messing with cowl flap hardware, which if not correctly rigged, won’t operate properly once the cowling is reinstalled.

Once you properly torque the new oil filter to the engine, it’s time to perfect your safety wiring technique. It’s not just a matter of twisting the wire until it’s snug. The diameter of the safety wire and the number of twists you make is critical.

When we research the NTSB accident records for our used aircraft reports each month, we inevitably find instances of engine failures because someone didn’t properly wire the oil filter (or didn’t attach the safety wire at all) and it vibrated loose—dumping all the oil from the engine. Again, it’s not difficult work, but you need to know proper technique.

Once the old filter is off, you’ll have to inspect it for particle contamination, while also correctly obtaining an oil sample for an accurate analysis.

The regulations say you can service your own landing gear struts, but botching that chore can ultimately cost you lots of money. Consider that the Oleo struts commonly used on main landing gear assemblies are serviced with a high-pressure air or nitrogen source. Get a little too aggressive with refilling them and you can destroy the strut.

Moving inside the cabin, the FAA says you can repair upholstery and decorative furnishings—and many aging aircraft can really use it. But, don’t fall into the trap of using unapproved components. I remember one owner who did a wonderful job of replacing the seat upholstery and sidewalls in his Piper Comanche, compliments of the shop that specializes in custom boat interiors. The components were waterproof—but not fire retardant—and in violation of the FARs, which specifically address fire-retardant qualities. He ended up tearing it all out and installing an approved aircraft interior.

On the topic of fabric, you can make simple patches to the skin of fabric aircraft as long as it doesn’t require rib stitching or the removal of structural components or control surfaces. Even so, fabric repair is specialized work and an acquired skill.

Do the Visual

Don’t underestimate the value of visually inspecting (not disassembling) the systems you aren’t approved to work on. A sharp eye between annual inspections can save money and keep ahead of breakdowns.

Do you look at the magnetos? They’re generally a 100-hour or yearly inspection item, but some deserve more attention. Trouble can be easy to spot: oil seeping from the casing. Plus, the housing might break free from the engine. I remember finding a pressurized mag hanging loose inside the cowling of a Centurion. That same aircraft had an obvious hairline crack at the base of the turbocharger. A smart pilot would agree to a further inspection, but this owner pilot was convinced that a cracked turbo was a deferrable item. I refused to fly that aircraft and his IA refused to sign it off. He flew it away.

While you’re inspecting the exhaust and turbo, eyeball the flexible induction hoses and the fittings at the turbo inlet oil lines. You don’t want the hose to get ingested by the turbo and it does happen.

Keeping the engine bay clean will help you spot oil leaks early. Just because the engine isn’t spewing oil on the hangar floor doesn’t mean it isn’t leaking, unless the engine is round—in which case it’s always leaking.

Some oil may be blow-by from breather assemblies or from the engine spitting out overfill, but you’ll need to follow the leak to the source to know for sure.

Oil isn’t the only leaking fluid that drips. Inspect fuel injector lines and clamps and put a wrench on the securing nuts on the spider to each injector. See any leakage? Raw fuel pouring around the injector manifold is what inflight fires are made of.

Avionics Work

Just because you successfully built a Heathkit project in high school (I failed) doesn’t make you an avionics technician, which often requires a repairman rating.

Still, the FAA limits do-it-yourselfers to what used to be basic avionics tasks, like removing and reinstalling a radio that’s self-contained in the radio stack. As simple as it may seem, you can screw this up.

Generally, radios are secured to the mounting trays or sleeves using lockdown cams, which are often accessed with a hex wrench from a hole in the radio bezel. Stick a blunt tool in the wrong bezel hole and you might trash a display photocell.

Plus, getting an avionics component out of the panel isn’t always the difficult part, but getting it back in might be, especially when the radios are tightly racked. It if doesn’t seat into the connector (or you break a contact pin in the process), you’ll have intermittencies—or the system may not work at all. You’ll be paying for a teardown and wiring repair.

Owner-performed software modifications are questionable because they’ll likely require a change to the previously approved flight manual supplement. The process might require reprogramming and calibrations.

Unless you have a current manual, you’ll be messing with data that can take down the entire system architecture. Service centers are trained on maintaining OEM glass like the Garmin G1000 and Avidyne Entegra and they should do the updates.

Button It Up

But before you do, secure a good relationship with a competent A&P mechanic or repair station and let them know what you’ve done. Their guidance can be a backstop for your repair actions.

Be respectful and mindful that the shop is a business, with lots of overhead and regulations to deal with. If you ask to borrow its tools and shop floor space, you might be turned away, but don’t take it personally. At some shops, insurance policies prohibit non-employees on the maintenance floor.

All is not lost. Good shops will recognize you are a paying customer because as the sidebar above explains, you’ll still need a shop to sign off annual inspections and major modifications, even if you decide to earn your A&P rating.

Years ago there was a guy at the local airfield who was convinced every maintenance shop and FAA inspector was out to screw him and every other aircraft owner. He once remarked that annual inspections are a scam.

While he wasn’t an A&P technician, everyone presumed he did his own maintenance, using his inventory of new and used parts. As most of us expected, he eventually flew himself to a smoking hole after the critical engine on his twin failed during takeoff.

While this exaggerates even the extreme consequences of do-it-yourself preventive maintenance, be realistic about your wrenching abilities and know when to bring the aircraft to trained professionals.

Larry Anglisano
Editor in Chief Larry Anglisano has been a staple at Aviation Consumer since 1995. An active land, sea and glider pilot, Larry has over 30 years’ experience as an avionics repairman and flight test pilot. He’s the editorial director overseeing sister publications Aviation Safety magazine, IFR magazine and is a regular contributor to KITPLANES magazine with his Avionics Bootcamp column.