GOOD.... THEN NOT SO GOOD....

Thursday 30th September

Aircraft: Cessna 172R, ZK-WAM

POB:      4

Altitude: 172' asl (on the ground at HLZ)

Weather: Broken cloud at 2500', wind 010 at 12 knots, QNH 1019 - forecast rain from 1200 local

Well, it didn't look good for a cross country so, instead of taking my 3 passengers (youngest daughter, her boyfriend and his mum) for an expensive coffee somewhere I decided a local flight was in order.  All preflight, passenger briefing, run-up and pre-take off checks done, we had been cleared to the North-East, to line up on 36L (once a couple of landing planes were down), and stay on the runway heading until advised.  So far, so good, and cleared for take off while lining up.

It stayed good for only a few more seconds.  With a heavy plane and the short runway, I elected for a maximum performance take-off, opened the throttle on the brakes and then let go.  It was about 5 seconds into the take-off run when the white noise started.  All I could hear while lifting off was a torrent of static and the very faint voice of the circuit controller talking to other traffic.

No time to do anything at present, I thought, just get the aircraft into a climb, clean up and the reassess the situation.  I carried straight on as cleared but now could barely hear anything over the static.  I levelled off at 1200', closed the throttle to 2300rpm and the radio became a little clearer.  However, the controller could neither hear me, nor detect my transponder (yes, it was on mode C).  With the controller talking and me responding with transmit pulses I got myself onto the Scott departure track and requested a return to land.

With the throttle closed further to about 1900 rpm the radio became clearer and we could now talk to each other.  I had checked all the headsets, circuit breakers and changed radio sets (two radios on WAM) and all had made no difference.  I tried the throttle again and back came the static at anything above 2000 rpm.  Having been cleared right hand downwind for 36R, the approach went well, holding at about 65 knots on final with 4 up to try a precision landing and get off the runway ASAP - there was a fair bit of other traffic about.  That worked well, I stopped with plenty of room to taxi off at "Charlie" and back to the club.

I reported the problem to instructor Peter who went off to take WAM up to assess.  I was offered JGP as that was free but there was no time for another flight.  We all went back to the car just as a few spots of rain started to fall so probably all for the best.

About an hour later I phoned the club and spoke to Peter.  He hadn't got up for a test flight as the weather turned bad pretty soon after we left.  So, no diagnosis as yet but I reckon it must have been interference from the engine as below about 1900 rpm all was fine and above 2100 rpm I could hardly hear the tower and they could neither hear me nor detect the transponder.  Interesting... anyone have a suggestion?

I did get up to fly earlier this week, on Monday with the best weather for some time.  I took the Arrow for a bit of manoeuvring and a few circuits off 25 in a moderate 12 knot or so westerly.  This all went well apart from my first steep turn which was a bit "rusty" but all landings were good.  So, things did go right at least once this week.