Spat, Spat, Spat, Engine Problems @ 500 Feet.
By: Doc. Green

Note: The plane involved here is not a Challenger. It is an Xair Standard with a Jabiru 2200, 4-cylinder, 4-stroke engine.

Danged if I didn't have a pretty serious engine problem today (Oct 31, 2005), but I was lucky in that I didn't break or bend anything, and I managed to keep the dirt out of the pitot tube.

Early in the afternoon, Capt'n Ted and I adjusted the valves and torqued the heads on my Jab ... routine maintenance. Nothing unusual; no problems; a routine operation. Then we set out to fly a bit. I was climbing out and had reached perhaps 500 feet agl, off to one side of the runway, when suddenly I got the dangedest sound through my headset. It sounded like an ol'timey hit or miss engine, sort of spat, spat, spat, but real loud.

Thinking I had an electrical problem, I reached down and turned up the squelch on my intercom, but it wouldn't cut it out. Then I noticed that the engine seemed to be running rough, and the noise was coming from the engine. I throttled back and immediately started a turn back toward the runway. My first thought was, Where's Ted? He was coming out behind me. OK, I've got him. He's down much lower than me, and hopefully will get out of my way, ... which he did.

My immediate problem, with the engine back to idle and still making the horrible noise, was that I was way high and fairly close in. I started doing a bunch of S-turns to get down when I noticed that Ol' Man Billy with his golf cart is now smack in the middle of the runway. And he can't half see, so this is going to be interesting. But I kept doing the S turns to be sure that I "hit the slot" between the trees at the end of the runway.

My mind was focused on "Hit the slot" first and worry about Ol' Man Billy next. So after some pretty wild maneuvering to hit the slot and after I knew I had it made, I realized I could either land short and go around Mr. Billy, or I could try to add power and land past him. So I gave it a bit of throttle, and it revved up. Still making the noise, but it was making power. So I flew over and beyond him and finally bounced that thing onto the good solid dirt. I taxied back down the hill, shut 'er down, and sat there, wondering what the heck was going on.

Ol' Mr. Billy drove up, ... "Doc, it don't sound quite right." Yeah, I know. At any rate, Capt'n Ted landed and we started looking to see what might be wrong. Nothing obvious on the outside. Thought the magnets on the flywheel might have been hitting the iron core of the magnetos, but ... that wasn't it. When I tried to crank it after we had adjusted the magneto gap, it backfired like an Ol' 12-gauge shotgun.

Must be something else. So we started digging deeper. Removed a plug from #4 cylinder. Plug was black. Not good. Removed the rocker arm covers to look at the valves for #4. OK, right where we left them. But when I removed the cover from #2 cylinder, I found the exhaust valve tappet and jam nut laying at the bottom of the rocker case, with the pushrod end happily lying there in the empty hole. "Ah-hah," I says. "This don't look quite right!"

So what happened is, the thing came unscrewed. Why it came unscrewed is because the jam nut was not tightened down against the rocker arm. This is where the mystery comes in: why was it not tight? I stood and watched Capt'n Ted put the muscle on the wrench, and we checked the clearance after tightening it down. I know we did this, because we always do them all the exact same way. Why was it not tight? Don't know. Maybe his wrench jammed against the case. I don't know??? So, at any rate, we looked at all the other valves, checked and double checked everything in that area, and then buttoned it back up.

This time it cranked normally. Ran normally. I did a couple of test runs uphill on the strip, and everything seemed OK. At the end of my second run, at the top of the hill, I turned around and Capt'n Ted was taxiing up the hill behind me. I called him on the radio, "Hey Capt'n, what do you think I oughta do? Is it running OK? Yeah, I think so." Then he says, "You gotta get back on the horse ... " I took that to mean that I've got to fly this thing sometime, ... and now is as good a time as any. But I wasn't having fun.

I ran that sucker up one more time, got the RPM up as high as I could before letting her go, and off I went, ... just slightly puckered as I flew out over the trees. Flew about 20 minutes or so, everything normal, before I realized that I didn't have my jacket on and I was freezing to death! Landed shortly thereafter. So now I have had two engine events, with a 4-stroker no less.

In thinking back on my actions after I had throttled the engine back, I flew the plane by instinct. I don't ever remember looking at the airspeed indicator. Only thing I did wrong was to over-fly the plane. I was more aggressive with the S-turns than I needed to be. But that's looking back ... The sound in my headset was apparently being picked up by the mike and passed through the intercom. I was running a continual series of backfires.

Was I scared? No. Too busy looking for Ted, trying to lose altitude, and worrying about Ol' Man Billy. However, after I got out of the plane and was talkin' to Mr. Billy, I just started shaking. Sheeeish! And that's my story. I feel lucky to have gotten down OK, and I'm a bit more of an experienced pilot now.

Afterthoughts and Reflections

  1. In discussing with Capt'n Ted the question of how the jam nut somehow did not get adequately tightened, it now appears that the box end wrench he was using must've been wedged between the jam nut and the rocker case so that the force applied to the wrench was not transmitted to the jam nut. It's a tight fit to get the wrench on the nut, and we have had wedged wrenches before. This time, however, it was not noticed. I accused Capt'n Ted of sabotaging my plane and insisted that he pay for my breakfast over which this discussion was held.

    It goes without saying that all maintenance procedures, no matter how routine, should be done with utmost care.

  2. Because of the lack of emergency-landing spots in the immediate vicinity of the field, I had made it a practice to turn slightly to the right after getting above the trees, and then, while climbing, to gradually circle back to the left across the extended centerline of the runway, staying within gliding distance of the field.

    This time, it paid off. The problem developed when I was on the circle back to the left, directly in line with the runway. I knew I could make the field. In fact, I had excess altitude to lose.

    Some pilots make it a practice, after doing ANY engine work or significant maintenance, to stay within gliding distance of the field for an extended period, perhaps for 20 minutes or so, to be sure that everything is operating normally. Not a bad idea.

  3. The other "engine event" that I referred to above resulted from fuel starvation on takeoff from a 5,000-foot runway. This occurred when I had only a few hours on the plane and was caused by a faulty fuel pressure regulator. The "unscheduled landing" was a non-event because I had 4,000 feet of runway still in front of me when the engine bogged down.

    Even though 4-stroke engines are supposedly more reliable than 2-stroke engines, simply having a 4-stroke engine doesn't automatically get you the greater reliability. All parts of the system must be properly designed and maintained. A fuel delivery problem or an issue with a throttle cable, for example, will render a 4-stoke engine just as silent as any 2-stroke ever was.

  4. Finally, I must admit that I almost screwed up by going too far away from the extended centerline of the runway while doing the S turns on short final. I went almost too far to the side, and I was lucky to get back. A better approach would have been to abandon the S turns and do a slip once I was fairly low and close in. The Xair slips like crazy, and I do slips all the time, sometimes to within a few feet of the ground. But this time, when a slip would have been good, or even wonderful, I didn't even think of it!

Doc. Green