During dual instruction in a Cessna 152 the sequences was gliding and gliding turns in the training area. . We were several hundred yards off the coast at 3000 ft. The sea was calm. A small river inlet adjacent to a few holiday houses had several small yachts floating at anchor in the mouth of the inlet. A sports oval was also adjacent to the holiday homes. The student had about three hours flying experience. The aerodrome we departed from was about three miles away.
We were maintaining about 60 knots while gliding and around 1500 ft I had the strong impression the propeller was slowing down more than expected for closed throttle glide and carb heat control in hot position.
As I scratched my head over that one, I told the student to apply full throttle and climb away. He pushed open to full throttle while simultaneously raising the nose to the climbing attitude for 60 knot climb. The prop slowed and stopped and at that point we were around 1000 ft above the water.
I took control and turned towards the river inlet planning to ditch near the yachts. While the local aero club had a VHF set in the club house there was no guarantee anyone was there. I switched to the main ATC radar frequency and at the same time dialled 7700 into the C152 transponder that covered a nearby international airport and got a quick Mayday out saying I was ditching at the mouth of the XXX River. This was quickly acknowledged.
Thought about trying for the sports oval which was near the shore at the mouth of the river but it was obvious it would be safer to ditch rather than be tempted to stretch the glide. I told the student (who had no idea of the seriousness of the situation of course) to check his harness secure and to crack open his door. I also told him to lean back in his seat so that I could lean over to his side and operate the primer pump.
The primer pump on that particular Cessna 152 had a history of seizing making it hard to pull it out and push it in. No one had ever bothered to write it up before. Typical GA operation. Fortunately I had written up the primer defect a few weeks earlier and the maintenance people lubricated the shaft and fixed it.
We were down to 400 feet by the time I was able to unscrew the handle of the primer and give it one full burst of prime. Then I turned the starter key and the engine started immediately and I was able to get full power straight away. I got the climb going at 300 ft and saw the look on the crew of one yacht looking up at me as we passed over where we would have ditched at the mouth of the inlet.
We cancelled the Mayday and after landing safely at our aerodrome, I wrote up the defect in the maintenance document. A new instructor then admitted he had had the same trouble a few days earlier when the prop stopped in that aircraft when he was doing stalling practice at 3000 ft in the training area. He did not attempt to re-start it by using the starter motor but instead dived the aircraft to get the prop to revolve which it did.
He failed to write up the defect because he said this was his first instructor job and didn't want to make waves with the aircraft owner or the CFI. I pointed out to him that because of his failure to write up the defect we very nearly were forced to make a bloody big wave if we had been forced to ditch...