Blowing a Valve Over the Post Office

I was chatting with a fellow on twitter today who had a gear down problem, and made mention of the fact that sharing his experience could be a great learning tool for others. This got me thinking a bit, and I thought, wow, I should probably do the same… and with almost 30 years of flying I have quite a number of them, so here goes. (this is from 1985)

I knew the engine was slightly over TBO, but the compression figures were still looking good. We’d done a top overhaul about 350 hours previously, and were hoping to eek out another 200 or so, before tearing it done for a major overhaul in the fall. A student had come back in from a solo flight, and was crabbing about poor climb performance. Since the density altitude and humidity was pretty high that day, it would have been easy to leave it at that, but we decided it best to check things out before sending out the next student.

As such, I did a ground run up, and checked max rpm, and it was right on the money as far as history goes and such. There were no unusual noises, nor was there any roughness noticed at all. A pre-takeoff checklist also indicated no problems whatsoever.

I then proceeded to taxi out, and did a second pre-takeoff check at the pad, where everything checked out just fine. Tower clears me for immediate takeoff… there is a DC9 in position and hold on the intersecting runway. During the takeoff roll, everything seemed normal… acceleration was typical, as was the climb to about 100ft, and then things started to go south. My first thought was carb ice, being it was a humid day, and I’d often run into such before with this particular aircraft. Of course, by that time, I’d run out of runway, and was right on top of the post office… and upon hitting the carb heat, it was pretty obvious icing was not the problem this time.

Directly in front of me is a residential neighborhood with wires everywhere. To my left and somewhat behind is the remainder of the intersecting runway… too bad, the DC9 had already been cleared for takeoff, and no way was I going to risk a midair, to say nothing of wake turbulence. To my right and slightly behind, is a long street, with a fair amount of traffic, but no wires. Fortunately, since about day 2 of training, I could hear my primary instructor hollering in my ear, “you just lost your engine, where are you going to land”, so I at least knew before takeoff what my options were.

On a positive note, since the engine is still producing some power, I am still able to climb albeit exceedingly slowly. In addition, I’m also making a very shallow bank towards that road. I dont know when or if the engine is going to quit but I figure each foot of altitude gained is a positive. I also knew of a second option, namely that when the long road ended, if I continued the bank another 30 degrees, there was a second road without wires I could use.

As I rolled out of the bank over the road, at now an amazing 200 feet, I called up tower, and said I had engine trouble and needed to land asap. They saw I was in trouble, and cleared me to land any runway… sure, I’d like to use a runway too, but a road will do, turf would do even better, as long as its long and flat enough… but houses or wires would really suck. I also run through the emergency flow at this time to rule out any other problems.

Fortunately, I’m still climbing, and now I’ve changed my plan to the diagonal road without wires. It was looking to be a lot better choice than having to try and land between cars… and if I kept climbing, I might well be able to make it back to an intersecting runway. Then again, a road at a 30 degree angle, puts said intersecting runway at a near 120 degree turn… and no, I’d rather risk a near zero traffic road without wires, than a 120 degree steep turn at low altitude.

Decision time is now coming up again… the engine is still producing power, I’m at roughly 300 feet, and my ability to land on the road will be questionable shortly as it takes an abrupt right turn. On the other hand, at this point, even if the engine quits I can make the airport boundary, and put the plane down on turf even though it will make for an interesting crosswind landing.

Knowing that the airport boundary and turf is assured, I now start a shallow bank to line up with one of the runways. I leave the power setting alone, and continue to try and climb. In fact, I kept power on until I was assured of making the runway. The landing was uneventful, as was the taxi back to the hanger.

ImageI got in, and after shut down, including a shut down mag check, I pulled the prop through to confirm my suspicions. One cylinder had no compression… and based upon the air rushing through the exhaust system, I figured an exhaust value was toast. After pulling the heads off, it turned out the valve itself wasnt massacred like the one in this photo, but the poor valve seat was a goner in a huge way. It was interesting, when we did the major… short of mandatory replacements, and the heads, the rest of the components were well within spec. Its even more interesting that the top overhaul failed at a mere 350 hours, when it should have lasted close to twice that long.

So, what did I learn…

  1. Expedited takeoffs while a nicety can serve to massively limit ones options should one run into trouble. I was in the habit of accepting them automatically.
  2. Its critical to know ones airfield, and have a number of game plans in the event of trouble. Granted, scoping out the area for wires and suitable roads is not always possible. In such an occurrence, it is often best to take the first reasonable choice, rather than making a turn only to find out the 2nd option is loads worse than the first.
  3. Being I knew the glide ratio of my a/c with the power off, and the prop windmilling, I had a reasonably decent idea of how far I could travel subject to my altitude. It should also be noted, that once one is in ground effect, if the surface is flat, the glide ratio often substantially increases. On the other hand, there were multiple embankments, and drainage ditches, expecting to use ground effect would be a bad deal in this instance.
  4. In the back of my mind, I knew I was likely causing more damage to the engine, but figured better it, than the airframe, or worse me. Valve guides are dirt cheap compared to an ER visit, even back then.

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