We met at Barton and pulled the Chipmunk (Sierra Lima) from the hangar. The weather wasn't brilliant, but it was quite flyable. We pre-flit, strapped in, and fired up.
Once the oil temp was up, we taxyed to the hold for 09 (the only one of Barton's runways which points directly at a built up area). Checks complete,
we lined up and I applied full power. Tail-up, SL accelerated smoothly over the wet grass and I let her unstick at 45 knots, holding her down just above the surface in ground effect until we had 60 knots, then eased the stick back and climbed out at 70 with a good rate of climb.
As we crossed the upwind fence, SL gave a mighty cough, which I felt through the controls. Could be a bit of water in the fuel - I made a mental note to stay in the circuit until I was happy with the engine, and continued ahead (no other options at that stage, anyway). A couple of seconds later, now about 300 feet over the built up area, the steady blattering roar of the Gipsy Major engine deteriorated into a series of loud pops, bangs, and surges, accompanied by much vibration. I could no longer read the instruments as the panel vibrated, or hear the radio (despite headsets) because of the cacophony from up front. I levelled off immediately, holding full power (such as it now was...) to let the speed build as much as it could and started a very gentle slightly descending left turn transmitting "Sierra Lima immediate return".
I couldn't hear the reply of course, but knew there was at least one other aircraft in the circuit in front of us. If we could turn beyond 90 degrees before the engine failed completely I thought we could probably continue a gliding, descending teardrop turn from there and get back in somewhere on the airfield. Or failing that, into a field north of Barton. Crashing into the built up area as at first feared seemed unlikely now, thankfully.
In the turn I noted the cemetery rotating around the left wingtip and looking ominously close. Then three brilliant white swans in perfect formation swept gracefully under us; I could swear their beady eyes were swiveled upwards towards the noisy, banging, shaking, farting red beast descending towards them.
Rather than the engine failing completely as I had feared it might, the misfiring actually became slightly less severe and I realised we could hold
height. So I stopped the turn after 180 degrees which put us on a close-in low-down left hand downwind leg for the active runway, 09. I transmitted "Sierra Lima, rough running engine, immediate return" in case the tower and the circuit traffic hadn't got the message the first time.
Again, I couldn't hear the reply. I pulled on full flap, turned base very close in with the 09 numbers on the left wingtip while transmitting "Sierra Lima close-in left base" for the information of any other traffic that this is now MY runway AND I AM GOING TO LAND ON IT. Once I knew we could get in I closed the throttle, let go a very old breath, trimmed for 60 knots, and continued a steep gliding left turn right down onto the runway.
We taxyed, followed by the fire tender with its blue flashing light, straight to the engineer's hangar. They did some ground runs - lots of misfiring (but nothing like as bad as it had been in the air) with flames and white puffs of unburnt fuel from the exhaust at high RPM, black smoke at low RPM.
As a postscript, the aeroplane was 'fixed' by changing the plugs, but it still wasn't running as it should. Later, we applied a mod so we could use 'modern' plugs, which improved things a lot. But what really fixed it was, several months after the above, a mag failed (on the ground) and after it was changed we had no more intermittent mis-fires - or worse.
I don't think either of us will ever forget those surreal white swans flying gracefully through the middle of our drama.