Engine Roughness after Take Off

The only real emergency is a situation you haven't been trained to handle. 

My CFI told my daughter that many years ago when she interviewed him for a school project. The only real emergency is a situation you haven't been trained to handle. That phrase has stuck in my head for many years. Especially now that I'm training other pilots and future pilots. As I train them I try to make sure my pilots don't have a real emergency.

One of the situations I commonly train people to troubleshoot and handle is a rough running engine with some power loss. This is much more common than complete power loss. Once I'd experienced a engine that seemed to be running a bit rough with no power loss. However, I'd never experienced a severely rough running engine and major power loss. Fortunately, my training, and the training I've been providing, did prepare me for the situation when it happened today.

This afternoon I was in a Piper Arrow with a commercial student. We were planning on doing Chandelles and Emergency Descents, maneuvers Commercial Pilot candidates must master. We taxied out to the run-up area and he did the run-up checks. Everything, including all magneto and propeller checks, seemed fine. He requested take off and off we went.

On the take off roll my student commented he needed more right rudder than he expected. I thought the engine seemed to be running strong but the climb out performance wasn't as good as expected. He brought up the landing gear and it seemed to take forever to get to 500ft AGL. I kept checking my student's airspeed but he was climbing at Vy, which should have given us at least 800fpm climb rate. Just as we gained enough altitude to turn crosswind the engine started running rough, rougher than I'd ever felt before.

"The engine's running rough!" the young man said. I told him to turn downwind and not change anything until we got over 1000 AGL. Our climb rate was down to 100fpm, with occasional increases to 500 fpm in an updraft. My initial thought was the propeller was somehow out of balance because I felt vibrations throughout the plane. I told him to keep climbing and then turn off the fuel pump and pull back on  MP and throttle to "25 squared" after we were abeam the numbers. This was deliberate because I knew I could do a power off approach from that location and altitude without issue. He did and the roughness seemed slightly better, though the climb rate was still pathetic. Time to troubleshoot.

We continued downwind, climbing slowly away from the airport. We both checked the oil pressure and temperature, fuel pressure, everything looked good. I was thinking now this was a magneto issue. The magneto check on the ground, just minutes before, was good, but I couldn't think of anything else it could be. With our climb performance so poor I didn't know what else would happen and I didn't want to climb away from the airport any further to attempt an airborne mag check. At about 2000ft MSL, I told the student to request a return to the airport to land.

We were cleared immediately to make a 180 degree turn and come back in to land on 31L. I told him not to change any other power settings until we knew we could make the runway if we lost complete power on our return to the airport. Once we were sure he slowly reduced the throttle and pitched for lower airspeed so we could slow down, get the gear down, and land. 30 degrees of flaps and a loooooong forward slip later we were back on the ground at RHV. The tower asked us if we wanted to stay in the pattern. We requested to taxi to transient to see if we could figure out the problem (perhaps a suddenly fouled plug?)

In transient we did a magneto check again and this time there was a major difference between left and right mags. Left mag ran smooth, right mag dropped 500 RPM and ran extremely rough. Just in case the spark plugs were fouled we ran up bit longer at high RPM and leaned aggressively. No difference. This was something we couldn't fix. We taxied back to parking and shut down the plane.

The problem could be a bad magneto, plug wires or a spark plug I think. In any case, it wasn't an emergency, even though it was quite disturbing for my student. For my own part I didn't feel nervous at all. It was a situation I'd been trained to handle.

As we debriefed on the event I told my student what my daughter was told that day, "The only emergency is a situation you haven't been trained to handle." That gave him pause as he realized even with his private pilot training he was trained to handle that situation. At the same time, he said, he was really glad I was there with him.