Running rough

My examiner, Eric, notwithstanding his relaxed, easygoing manner, was renowned to be strict but fair. In those days we feared the DCA, who ruled with an iron fist and showed no mercy to erring pilots. It was safest not to make any jokes – I learned this from dealing with their engineering side.

The engine began to run rough, the RPM fluctuated wildly, and the noise threatened to stop at any moment. It was a genuine emergency. . .

My general handling check had to be repeated because my instructor didn’t show me a particular manoeuvre, so I didn’t know what to demonstrate. The examiner was not allowed to tell me. So we landed, I was given the necessary information and after becoming airborne again, easily demonstrated the missing routine. Such was the pedantic approach.

I was desperate to finish my check flights as time was running out and the examin-ers were only available for one more day’s testing. I was very aware that if my flight checks were not completed now, the two year limit for these and my theory exams would expire before I had another opportunity to be flight checked. A totally new system was being introduced which would require me to re-sit all five written theory subjects (I had already passed four), and possibly redo check flights if I didn’t wrap things up now. The pressure was on! The following day we took off in the Aero Club Cessna 172 for a three hour plus cross-country, the last two legs being given to me after departure so I had to plan them in flight. I knew the Territory well, the navigation and accurate map reading didn’t bother me, but my stomach was still unhappy.

At that time of year, weather was not an issue so after climbing to 8000ft south of Darwin I levelled off. Soon after, the engine began to run rough, the RPM fluctuated wildly, and the noise threatened to stop at any moment. It was a genuine emergency, not induced by Eric! My eyes and hands went everywhere – mixture full rich and fuel selected to both tanks as I turned toward Batchelor airstrip, which was hopefully within gliding dis-tance. I checked the engine response to throttle but it continued to run rough and the RPM decreased to almost idle as we lost height.

“What will you do now Phil?” asked Eric.

I knew I should have declared an emergency and landed at the nearest suit-able airstrip as it seemed a complete engine failure could occur. To make matters worse, my signature was on the maintenance release as my private company main-tained the Aero Club aircraft. A correct decision now was vital to my future career and possibly our health if we were forced to land in the rough country below. My innards were far from happy.

“I’m almost certain I know what the problem is so the engine should run normally very soon!” As if on cue, the engine RPM increased, it began to run smoothly, and then responded perfectly to throttle.

My examiner looked at me and raised his eyebrows.

I knew that our next leg was to be flown at 500ft AGL over rough, uninhab-ited terrain. If the motor stopped then, we would have little time to find anywhere to land without writing off the aircraft. I somehow remembered the saying ‘fortune favours the brave’ and decided to back my engineering knowledge.

I answered Eric’s unasked question.

“Sir, this aircraft is almost new and the engine is not fully run in. It’s known that the pistons are fitted perhaps a little too tightly. Until they wear in, the cylinders can shrink and nip them when suddenly cooled, like when we levelled out after climb-ing. When the pistons also cool, or friction re-heats the cylinders, the engine runs normally. ” “I hope you are correct, Eric replied. “What is your decision now?” As I desperately wanted to complete the test today and was very confident about my diagnosis, I did not seriously consider turning back. I felt that nothing would be gained, the engine had to be run in.

“I see no reason for not continuing, our problem is over. ” Eric did not overrule me so I regained track as planned. I breathed a sigh of relief and concentrated on careful power and speed changes while returning to our cruise altitude. Likewise for the remainder of the flight, which passed without incident.

After landing we taxied to dispersal via runway 18, within a minute of my updated ETA. Eric asked: “Are you going to check the engine after what happened today?” “Definitely. I’ll pull the plugs immediately. You can look inside the cylinders yourself. ” “I’ll be interested to do that. ” Was he implying that the result of this check flight was in the balance? Upon inspection, we found the telltale scratch marks on the cylinder walls. The oil filter showed minute traces of metal, normal for an almost new motor. As a precaution, I also checked the fuel and other systems but nothing abnormal was detected. After this episode, the engine performed flawlessly until I left Darwin three months later, and I was told, completed it’s normal life.

Soon, the crucial govern-ment letter arrived – my check flights were OK’d and I could see the finish line to a new career. My most difficult theory exam, navi-gation, was passed several months later and a licence issued, about a month before the deadline. I felt I had earned my rite of pas-sage, even though I pushed the odds on my flight check. However, pilots without years of current hands on engineering experience shouldn’t second-guess mechanical problems while airborne! Once was enough for me and fortuitously, both my engine failures occurred in twin engined aircraft during my 45 years of flying in command.

“ I knew I should have declared an emergency and landed at the nearest suitable airstrip as it seemed a complete engine failure could occur.