The RAAF used 115/145 octane fuel in their Convair 440 Metropolitans. The high lead fuel gave greater allowable manifold pressure on take off. The downside was the plugs leaded up quickly soon after the run-up was complete. That, coupled with annoying break downs in the ignition harness at high MP often caused rough engine operation during the take off run. The rough running cleared up during the climb out - usually..
Until the RAAF Brass was convinced to obtain up-dated ignition harnesses from the US, we were plagued with occasional back firing and erratic engine operation during take off. Because the rough running always smoothed out after take off we got complacent and just kept on with these take offs. A new CO was posted in and I had the job of checking him out on the CV 440.
In those days Sydney runway 16 was the short one - around 5500 ft I recall, and of course ending at Botany Bay. The CO was in the left seat picking up ICUS hours (you had to have 150 hours on type before flying VIP's). I was QFI in the RH seat.
Nearing V1 one engine backfired loudly with oscillations of MP and RPM. The Old Man shouted "**** - shall we abort?" Mindful of the fall off into Botany Bay, and hoping it was the usual half-expected rough running I said "Christ! No Sir - keep on going!" As expected, the engine smoothed out OK.
Now back at Canberra, the US Embassy had their own aircraft - a USAF Convair 340 it was. The pilot was a highly experienced Major who had flown with the Presidential Flight in Washington. He and I were good friends and he passed a lot of knowledge my way on Convair operations. One hint being that during the run up (a lengthy process for the Convair) a good way to clear fouled plugs was to operate the primer switch with the engine at high power and in theory this would clean the plugs. The Convair had a primer switch for each engine and a prime-all-engine switch for squirting raw fuel into the manifold (or somewhere whatever).The Convair was known to suffer double engine failures in severe icing and the prime-all-engine switch delivered enough fuel to keep the engines going while the ice problem was sorted.
So at Essendon one day the pilot was running up one engine in the parking bay at the top end of runway 17 and asked the copilot to give the engine a squirt of primer for 10 seconds while the engine was at high power. The copilot said no problem Skipper and hit the prime-all-engines switch instead of the individual engine primer switch.
Now if you squirt raw 115/145 octane fuel into the high power engine that is no problem. But if a copilot stuff up occurs and it squirts into an idling engine there is a huge flame as the exhaust manifold catches fire and flames six feet high gush out of the open cowl flaps on top of the engine. It is quite spectacular really, as well as bloody scary especially at night.
Fortunately in this case the fire went out when the captain shouted crossly at the copilot who was persuaded to release the prime-all-engine switch under threats of a courts martial. Reports were filed by Essendon Tower and the Firies and the captain had no choice but to file his own report. The RAAF Brass got to hear about it and we finally got our new ignition harnesses and lived happily ever after. I forgot to say we had three such engine fires before the penny dropped it was a dangerous technique of cleaning spark plugs.
