Quarter Turn

By Robert N. Rossier, EAA 472091

This piece originally ran in Robert’s Stick and Rudder column in the November 2022 issue of EAA Sport Aviation magazine.

Dealing with in-flight emergencies is something we learn to do from early on in flight training. We practice everything from engine failures that can come at the most inopportune times, to stall recoveries, to electrical failures, landing gear failures, in-flight fires, and so on.

We generally consider these emergencies to be situations that arise due to no fault or failure of our own. But we also know the importance of a good preflight, and can likely suggest any number of items missed on a preflight that could cause us to suffer one of these emergencies. Perhaps the most obvious of these is failing to check the fuel level before flight, but there are others.

I recently read an FAA special airworthiness information bulletin (AIR-22-10) that dealt with the engine cowlings for turbofan-powered airplanes produced by Textron Aviation Inc. (previously Cessna Aircraft Co., Beechcraft Corp., Hawker Beechcraft Corp., Raytheon Aircraft Co., British Aerospace, and Hawker Siddeley). For those of us who don’t fly such equipment, it might be easy to ignore the bulletin, but it turns out we should be paying careful attention.

The bulletin deals with quarter-turn fasteners — commonly known by their brand names of Camloc and Dzus — used on the engine cowls of these aircraft. These fasteners make it quick and easy to remove the engine cowl for maintenance and inspection, and then to put it back on. Fastening and unfastening these mechanical devices requires just a gentle inward push and a quarter turn, and we can readily feel the fastener latch and unlatch.

As convenient as they are, the fasteners are replaced when worn or broken, and they aren’t all the same. It’s relatively easy in some scenarios to replace a failed, missing, or worn quarter-turn fastener with the wrong part — one that is too long, for example. To the untrained, it might seem the fastener is working properly, but the fact is that it isn’t holding securely, and the mismatch may be leaving an aerodynamic gap on the surface of the cowl. The end result, as depicted in photos in the service bulletin, includes cowl pieces being ripped from their intended position, sometimes smashing into other parts of the aircraft and causing serious damage.

While we might think the issue is confined to turbine aircraft capable of high speed, the sad truth is that even light general aviation aircraft can fall victim to quarter-turn fastener follies. One involves the myth that a missing fastener here and there is not an issue. Well, at some point, it can become a deadly serious issue.

Several years ago, the pilot of a twin-engine Piper Navajo neglected to replace a few missing fasteners on the engine cowl. He likely assumed a few missing cowl fasteners would not be an issue for his upcoming flight. That was the case until the engine cowl separated and wrapped itself around the horizontal stabilizer. The ensuing crash was fatal.

Quarter-turn fasteners aren’t the only ones that can come loose and cause damage. I’ve seen a loose screw on a prop spinner separate and put a gouge in a prop blade so deep the prop had to be replaced. That’s an expensive proposition in itself, but the result is nowhere near as bad as having a propeller blade separate due to a stress riser. Since that incident, I’ve made it a point to check the spinner for loose screws on every preflight.

A common practice for keeping other types of fasteners in place is the use of safety wire, and this is something we may be able to check for during preflight. An aviation maintenance alert for Cirrus SR20 and SR22 aircraft reveals how a missing safety wire can lead to a loss of control. As the alert explained, an SR20 crash in 2018 occurred due to the lack of a safety wire on an actuator arm attachment bolt. This allowed the bolt to loosen and fall out, thus disabling the left aileron and resulting in a crash shortly after departure.

More than a decade ago, a failed screw was the initiating event leading to the fatal crash of the P-51 Mustang Galloping Ghost at the National Championship Air Races in Reno, Nevada. According to reports, the screw was fatigued and corroded, and its failure led to a case of flutter and a cascading series of control linkage failures. We might attribute the accident to corrosion, fatigue, aging aircraft issues, and the stresses that come from flying at the edge of the envelope. But whenever we see corroded fasteners on our aircraft, we should take note and have the problem corrected.

As it turns out, improper or worn fasteners can cause a multitude of issues, which I learned firsthand a number of years ago. Immediately after touchdown, the aircraft (a BN-2 Islander) jerked and pulled hard to the left. I stood on the right brake to keep the aircraft on the runway and barely succeeded. It turns out the bolt securing the scissor mechanism on the left dual wheel assembly had mysteriously detached, allowing the wheel assembly to rotate 90 degrees from the direction of travel. I thought I must have missed something on the preflight, but an investigation revealed the cotter pin through the bolt and castellated nut was still there — sheared off from the force. Such an issue can develop when the threads on the nut are worn, or an incorrect nut is used on the bolt — items that the typical pilot is not likely to determine in a preflight inspection.

Harrison Ford’s crash in his vintage Ryan Aeronautical ST3KR in March 2015 was reportedly determined to be caused by a loose screw in the main metering jet in the airplane’s carburetor — not something that would ever be found in a preflight inspection. The result was a loss of power after takeoff that caused him to make a forced landing on a golf course.

No matter what they are intended for, loose screws can end up just about anywhere and interfere with operations in ways we might never imagine. Earlier this year, the pilot of a Mooney M20 E Super 21 suffered an engine failure when the pilot attempted to change fuel tanks. As he attempted to rotate the fuel selector lever through “off” to the other tank, it jammed in the “off” position, forcing the pilot to make an off-field landing in a pasture. The jammed handle was found to be caused by an errant #8 PK sheet metal screw from somewhere that became lodged under the fuel selector handle.

The bottom line is that we and our mechanics share a responsibility to ensure the integrity and airworthiness of our aircraft. Should we see (or not see) something — such as a fastener — that just doesn’t look or feel right, we need to ask questions and bring it to our mechanic’s attention. Oftentimes, all it takes is a couple of minutes — or maybe just a quarter turn — to remedy a situation that could otherwise result in a serious incident or fatal crash.

Robert N. Rossier, EAA 472091, has been flying for more than 40 years and has worked as a flight instructor, commercial pilot, chief pilot, and FAA flight check airman.

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