Top 10 Overlooked Maintenance Items — What Can Happen and How to Prevent It

By Lisa Turner, EAA Lifetime 509911

This story first ran in the September 2019 issue of EAA Sport Aviation.

The day was perfect for flying. The bright sun warmed the field as it rose over the close-cropped grass sparkling with dew.

“A great day for the fly-in,” said Roy, one of the homeowners living on the 3,000-foot grass strip.

“Yes,” said Wendy, a neighbor. “I’ll bet we get 20 airplanes in today, it’s so nice.”

They began preparing for the crowd in one of the large hangars.

An hour later, the airplanes began to arrive. Those who had driven in gathered to watch. No matter how many times they heard the round engines get more distinct in their guttural music as they approached, the reaction was always the same: overwhelming excitement.

A Navy-schemed Stearman arrived first. Behind it, a Great Lakes followed, and then a Cub. Then came another blue Stearman, a Taylorcraft, a RANS S-7, a Van’s RV-12, and a Champ. The air was full of airplane symphony. Wendy and Roy leaned back in their lawn chairs and drank in the sounds and sights.

A short time later, they heard another airplane and looked up to see a bright white Waco UPF-7. It was doing a flyby. It thundered past just above the field and then did an abrupt pullup.

“Impressive,” Roy said.

“Wait,” Wendy said. “Look!”

Something had gone wrong. The UPF-7 seemed to wobble in the air.

“Look at the right side,” Wendy said. “I think a flying wire came loose.”

The Waco leveled out, but the pilot was clearly having trouble. He made a turn to make another approach, but the airplane was pitching and rolling.

“I don’t like this,” Roy said.

The crowd became attuned to the calamity unfolding and stopped what they were doing to watch the Waco as it made an unstable approach to the field. They could see one of the flying wires whipping about as the airplane came in. There was a collective sigh of relief as the pilot concentrated on his landing and slowed the plane to a stop.

“Whew,” Wendy and Roy said at the same time. They walked over to the Waco.

“Wow, that was exciting,” the pilot said.

“I guess so,” Roy said as he looked at the broken flying wire ends. “Looks like it broke at a nick.”

They saw a deep indent in the wire where something had hit it.

“You know, that’s one thing on my preflight I never check,” the pilot said. “The wires. I didn’t know that could happen.”

“That, and the tension should be checked during inspections,” Roy said. “What was the tension set to?”

“I have no idea.”

“It would be good to make a note to add that to the inspections.”

“I definitely will,” the Waco pilot said.

Another all’s well that ends well story, but with some important lessons.

Humans overlook things. That’s why we use checklists. But, even when we use checklists, we overlook things.

I asked a cross section of A&P/IA mechanics what items were most overlooked on an annual, condition, or 100-hour inspection. I figured that elevating these things to its own listing might help prevent them in the future for those who like checklists and don’t want to leave anything off. Although most of these items are not exciting, if overlooked they could get exciting quickly, especially if they are overlooked year after year. These items come from antique and classic aircraft, current GA aircraft, and homebuilt aircraft.

Top 10 Most Overlooked Maintenance Items

1. Hardware. You knew this already, didn’t you? This is the top issue with all the airplanes the mechanics worked on. It included:

Wrong nuts in the wrong places. An example is a nylon lock nut in a hot spot near the exhaust instead of a high-temperature nut. Another example would be a castellated nut with the cotter pin missing.

Loose or missing jam nuts. It’s not just that the control rod could loosen, it’s that the jam nut also loads the threads preventing thread wear.

Missing or incorrectly routed safety wire.

What could happen: Components could fall off the airplane. Okay, that sounds extreme, but at the very least components could loosen. Then the vibration will accelerate failures.

How to prevent it: Go back to the owner’s manual or the instructions/plans that came with your airplane and make sure your checklist reflects the right hardware in the right places. Make sure the items are on the maintenance list.

Use Torque Seal. This gives you a “visual witness” to let you know if things are loosening. Don’t confuse Torque Seal with the various types of thread locker.

2. Control surface travel and freedom of movement. When was the last time you put a protractor on a surface? We’re supposed to check this at the annual, condition, or 100-hour inspection, but it often goes overlooked.

What could happen: Cables can loosen or become jammed. This, in turn, will change the flying characteristics of the aircraft. A jammed cable could lead to a problem controlling the aircraft, especially on takeoff and landing.

How to prevent it: While surface travel should be inspected and set correctly during maintenance inspections, freedom of movement and orientation should be checked on every preflight and runup. After maintenance, pay particular attention to the control direction of travel. There are enough stories of airplanes coming out of service with the controls rigged backward, so double-check it.

3. Cables worn and pulleys binding. The things that are most hidden from view will be the things that we overlook the most.

What could happen: Frayed cables will eventually fail, and they tend to catch on other things. Binding pulleys will aggravate cable wear and bind controls when you need them the most (Murphy’s law).

How to prevent it: Inspection, inspection, inspection. Use a flashlight and a cloth to check all cables. Move controls to check pulley operation. Take a good look at the pulleys. Can you spot unusual wear?

4. Incorrect tire pressures. Can you eyeball a tire and determine if the pressure is set to spec? Some pilots say yes, but I don’t have that special ability without a gauge. This often goes overlooked because the tires are hidden under wheelpants or accessing the valve is tricky.

What could happen: Both under inflation and over inflation can contribute to erratic handling on the ground, contributing to an accident.

How to prevent it: Don’t just eyeball the tire. Check it.

5. Worn brake components. Brakes get overlooked for the same reason tires do. We tend to assume that if the last flight was fine, the next one will be, too.

What could happen: In the roar of takeoffs and landings it’s hard to hear brake noise. If wear becomes severe, the brakes could fail or become uneven, contributing to loss of control on the ground.

How to prevent it: Check the pads, pucks, or shoes periodically. Pay attention to any handling issues or strange noises coming from the wheels. Look for leaks.

6. Worn seat belts. The mechanics I talked to said they routinely found seat belt webbing and hardware that was either very old or visibly worn.

What could happen: In addition to the high loading in an accident, aerobatics and other maneuvers could cause an old belt to fail.

How to prevent it: Inspect belts, anchors, and hardware. The label on the belt should be legible. If you see UV damage, worn webbing, or layers of fuzz, replace the belts or send them to an authorized repair shop. If you own a homebuilt, you have more latitude in terms of replacement belts. See “Strap In” in the June 2019 issue of EAA Sport Aviation.

7. Loose tailwheel assemblies. This is an item that generally won’t be found until flying characteristics indicate there’s a problem, like a shimmy or erratic operation.

What could happen: A loose assembly could bind and not turn freely when you most want it to on landing.

How to prevent it: On an inspection, unload the tail assembly (raise the airplane’s tail) so you can identify any looseness or other movement problems. Adjust to the manufacturer specifications.

8. Missing drain holes in fabric covering. Not having drain holes in the right places on fabric-covered aircraft can cause structural failure.

What could happen: Drain holes allow water and accumulated condensation to exit the interior of the surface. When the holes are missing, the moisture ends up trapped against the structure.

How to prevent it: Take a look at the drawings and instructions for the aircraft to identify where the drain holes should be. Generally, they are at critical low points. They are easy to add with a solder iron tip.

9. Flying wire tension is incorrect. Many owners sight the wires and push on them to assess tension. Like tire pressures, eyeballing does not give you enough information.

What could happen: Loose wires will create unwanted movement in the attach fittings. Wires that are too tight can fail anywhere along their length, including at fittings, and especially when nicked by stones or other debris. Wire tension that is higher than recommended can also lead to distortion and possible failure in flight.

How to prevent it: Use a tensiometer on flying, landing, and tail brace wires at every annual, condition, or 100-hour inspection and adjust to the specification the manufacturer has provided.

10. Compass fluid is missing. You may not even see that the fluid is missing, but the compass will tell you in flight.

What could happen: If the fluid has leaked out, you will experience erratic operation of the compass as the card tries to rotate on its pivot without fluid to dampen it. The compass diaphragm and/or the glass seal can be the cause of fluid leaking out. Without fluid, the compass is unstable, and it will be nearly impossible to hold an accurate heading, especially in turbulence.

How to prevent it: Tap the compass. If the fluid is missing, the card will go wild. Time for repair or a new one.

Take this list and cross-check it against the one you use for your condition, annual, or 100-hour inspections and your preflight checklist. It’s human to err. However, we really want to err as little as possible and enjoy our human, sky-filled pleasures as we continue to defy gravity.

Lisa Turner, EAA Lifetime 509911, is a manufacturing engineer, A&P, technical counselor, flight advisor, and former designated airworthiness representative. She built and flew a Pulsar XP and Kolb Mark III, and is currently restoring a Waco UPF-7 with her husband. Lisa is a member of the EAA Homebuilt Aircraft Council and Women in Aviation International. For more from Lisa, read her “Airworthy” column each month in EAA Sport Aviation.

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