Down To Earth

When the engine coughs (or worse), the creative mind gets cranking!


I’m going to begin this column with a few simple truths. One: If you own an aircraft, you know it is a mechanical beast, and as with all stuff mechanical, from time to time things break. And sometimes things break when you are airborne.

It has happened to me. To my illustrious husband. To my fellow pilots. If you fly long enough, even though I hope it does not, it may happen to you. The clan of homebuilders out there strive to create flying machines that are robust and truly safe, and we are always on the lookout for weak links-but even with all of our informal group safety management, we cannot prevent the occasional mechanical failure.

An example: The Van’s RV-10 engine installation puts the airbox at the bottom of the engine. Our installation, and quite a few others, uses a robust and efficient Airflow Performance vertical air induction system, attached to our common vertical-draft Lycoming IO-540 engine. The engine is nothing new, and the Airflow Performance system, developed by Don Rivera, has been working well for years, too.

How is it set up? In our installation the throttle body is pointed vertically straight down and the filtered airbox is the device that gives you the right-angle turn of the air to the air scoop on the front of the cowling below the prop. The setup calls for the airbox to be clamped, via a donut clamp, to the vertical throttle body under the engine.

Simple Problem

Truism number two: Simple problems can still be big. The powerful piston Lycoming engine that propels our RV-10 may be smooth enough at idle or in cruise, but the beast shakes like a wet dog on startup and shutdown. And that trait alone can cause issues over time with any appendages hanging off the engine.

Propeller vibrations can take their toll over time as well. And then there is the installation. This system must be mounted precisely as the manufacturer describes in the installation documentation. The donut clamp must be torqued such that the threads of its single bolt do not strip. Loctite between the donut and the throttle body it is clinging to can add one more level of adhesion. You want to create a robust bond because if the donut fails and the airbox falls off the throttle body, there are consequences.

Bob Newman, president of TCW Technologies and the proud co-builder and co-owner of an RV-10, found that out at about 200 hours. “At 7,000 feet it was almost like an electric motor had been turned off-the event felt almost digital,” he told me, still amazed months later. “I looked at the instruments to figure out what was going on. Saw nothing odd. But I realized we had no power.” He was on an IFR flight plan, but in VMC conditions, fortunately, and with Ocala airport nearby. “I declared an emergency with Jax Center, and the training kicked in,” he recalled. “I was very aware of where I was at, and I am always looking for places to land the airplane. It is a game we pilots play in our heads to keep on top of things. I started a turn back to Ocala within 10 seconds and acquired the airport visually.”

From there Newman ran through his emergency power loss checklist and noted one bizarre indicator: his fuel flow was off-the-scale rich. “I thought maybe we’d broken a fuel line and we were dumping raw fuel into the engine,” he explained. “I was incredibly tempted to shut the fuel off, but there was no smoke, no smell of fuel…I figured that shutting the gas off would not get me a restart and I had no evidence that the fuel could cause a fire in our state. Instead I messed with the prop. I just never thought to pull the mixture to idle cutoff, and in retrospect it might have worked to get me some power back given the fuel flow indication. Who knows? I just never processed it,” he continued.

Maybe you’ve practiced it and you know: running through an engine-out checklist doesn’t take very long. And if the engine doesn’t restart in that short, say 20-second, period, then it is time to buckle down and focus on landing the airplane. That means being sure you’ve established and trimmed for best glide at your current aircraft weight (yes, it varies). You should already be headed to an airport-you did that first-right? Calculating your glide and approach pattern to assure you make the runway is next on the list of things to do. High-performance gliders have the coolest little computers running that calculation constantly-we power pilots have eyes and a brain-that still works with practice.

Newman did everything right, even asking the Jacksonville Center controller to take on the burden of communicating with the tower, and he made it onto a runway at Ocala without hurting anyone or anything. That’s a good day at the airport, even if your engine quit before you shut it down.

Once safe at a maintenance hangar, he pulled the cowl and was startled to find his airbox had detached from the fuel injector body on the bottom of the engine and had been pushed back inside the cowl. The result was that the air entering the throttle body became extremely turbulent, which confused the fuel injector, causing it to default to full rich to cope with the problem. At 7,000 feet this killed his engine.

Should the donut clamp fail, safety wire now prevents the airbox from dropping off the throttle body on the author’s RV-10.

Simple Fix

Another truth pilots and builders don’t always want to ‘fess up about: fear is a motivator. Come on now, you knew that, didn’t you? Sure, we are all well trained to react with precision in the case of an emergency in flight. Well, that is the hope (and I’ve found it to be true most of the time, or there would be as many nasty airplane accidents as auto accidents polluting the local news on any given evening). There is just no way, however, that you can convince me that somewhere deep inside each one of us who has had to react to a sputtering engine, or worse, dead silence, has not felt that tightness in the pit of the stomach. Of course, then we got down to business making sure the flight had as happy an ending as possible. That’s because we practice for it.

The good news is that so much of the time our practiced emergency procedures work. Either the engine smooths out or restarts, or we can, following our hard-learned procedures, glide the bird to a safe and useable landing site-maybe even an airport runway. (I do like it when the airplane ends up back on a runway, especially if there is still enough momentum left to roll off onto a taxiway and keep the tower boys and girls from getting grumpy-they are usually annoyed enough at having had to clear the airspace for the emergency.)

Once safe on the ground, the analysis can begin in earnest, and that’s what Newman and the mechanics who greeted him in Ocala did. They saw the problem, they fixed it by reattaching the airbox to the throttle body, and then, after several static runs, they were back in the air. “We did, however, think about how to prevent this from ever happening again,” Newman said. “It was an interesting, sobering flight. Pretty quiet as I remember it,” he chuckled, thinking back. “I thought about the engine setup, and how to improve the design.”

Newman decided to reinforce his installation with safety wire. Yep, good old 0.040-inch wire now ties each filtered airbox bolt up to the mounting studs. It is a clean solution that does not impede the operation of the installation, but does prevent the airbox from completely dropping off the throttle body again were the donut clamp to fail.

The Share

Newman put his problem and his fix up on the Matronics RV-10 listserv, and lo and behold, it turns out others have had the same problem. In fact, the airbox on my RV-10 dropped off the throttle body at around 400 hours. The airplane was at 4500 feet when it suddenly began to run terribly rough and lose power, and the pilot (not me) saw the crazy high fuel flow and suddenly low EGTs. He pulled the mixture and throttle back, which resulted in a smoother running engine at a lower power setting. He drifted down at this lower power setting to a safe landing back at our home field, where he opened the cowl, discovered the detached airbox, and got to thinking. The picture shows you his solution was right on par with Newman’s.

It helps, too, to return to the original manufacturer’s installation instructions. They are clear on how to torque the clamp and bolts attaching the unit. But no one is going to argue with insurance in the form of a little safety wire. It can go a long way toward ensuring that vibration-affected appendages hanging off at all angles on Lycoming engines stay attached.


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.