My shortest flight ever

I was all geared up for a cross country flight on Anzac Day morning to Great Barrier Island. Me, my partner Susan and Chris were all strapped into ZK JGP. I got clearance to taxi to the runup area and proceeded out there. I was told the DI was non functioning, and needless to say it was about as much use to me as a roulette wheel. When I did the engine runup I noticed a large drop in rpm on the right mag. Not a problem, power up to 2000rpm and lean the engine out till it runs rough (while keeping an eye on the EGT so it doesn't get away from me). Reduce power down to runup rpm and recheck both mags, all fine. Complete the rest of the runup checks, taxi to the hold point and report ready. We are 3 up and heavy so I request the tarmac runway instead of the grass, get cleared across the grass to line up. We cross the grass and I line up. Complete the pre-take off checks, sit there for a few seconds waiting for the tower to clear me to take off. OK there is the call, repeat back the clearance to the tower, check with the passengers if they are ready to go, and on confirmation open the throttle. Check rpm, suction, fuel pressure, oil pressure, EGT, oil temp, all in the green. Airspeed comes alive, we have 1250m of wide sealed runway to use so I leave JGP on the ground till we hit 50 knots before rotating. Once the airspeed hits 55knots we take off and I set a nose attitude for a 65 knot climb.

Sounds like a normal takeoff? Yes it was, but as they say, things can change in a heartbeat. At 100feet AGL the engine coughs once. Both Chris and I instantly comment, "that wasn't good". I scan the gauges again, everything is OK. At 250 AGL the engine coughs again and the whole cowling begins to shake. At that precise moment in time the engine failure after takeoff procedure pops into my head. A split second later I realise that although the engine is running rough we are still climbing, so at the very least I can maintain altitude. A split second after that I say, "OK we're going to land," and I key the mike.

"Juliet Golf Papa has a rough running engine, request expedite landing Grass 07 Left." While that sounds impressive, I actually asked for the wrong runway. Fortunately the Tower saw what I was doing (I had levelled off into a left hand turn for a left base on Grass 25 left at 300AGL).

"Juliet Golf Papa, Grass 25 left, cleared to land."
"Grass 25 left, cleared to land, Juliet Golf Papa."
"Are you declaring an emergency at this time?" I remember thinking is the plane and passengers in any distress or real emergency? Am I able to land safely? After throttling back the engine had regained some smoothness and was not really any different to fly than any other normal approach. There was almost no wind so I didn't have a crosswind to think about.
"Negative."

I brought JGP in and landed uneventfully, not the best landing I have ever done, but under the circumstances I was pretty happy with it.

We taxied back to the Club, shutdown and I ran into the office and spoke with the head flying instructor who happened to be working that morning. He came out and after asking about possible carb icing took JGP out to the runup area and did a thorough runup before taxiing back in and parking it. His only comment was,

"Thats not a happy plane." I was told later it was definitely some kind of fault in the left magneto.

When I think back on what happened, if asking for the wrong runway was the only thing I did wrong, I'm pretty happy with how I dealt with the problem. I've thought time and time again about anything I might have missed that might have stopped me attempting to takeoff, but everything was fine after the runup, and the engine was developing full power as we started rolling on the runway. Its funny how aircraft engines like to wait till you are airborne before letting go on you.