What a lovely thread! Here's one of mine: In the late 1990's I was asked to fly a survey team out to Murcia to carry out some vertical aerial photography for land survey work. It was when digital photography was in its infancy and very expensive involving the fitting of a "digital back" to a conventional 35mm film camera. The digital photos obtained were stored on miniature hard drives and the contents of these were downloaded at night onto a portable computer which was fitted with a CD writer at X1 (Coo!).
Anyway, the first two days at Murcia were uneventful: we were granted permission to operate in the morning when the Spanish military were in control so we took off at about 10.00 and, following the guidance of the team's portable GPS routed out to the selected area. Here I flew a special search pattern to enable them to obtain their high definition digital photographs of the land in question. We returned after about 2.5 hours flying with a pile of miniature hard drives for downloading. The aircraft, a Partenavia, was then refuelled ready for a repeat of the exercise the following day.
All went well for the first three days then the weather changed. The sky changed from blue to grey, as did the Mediterranean, the wind got up and the rain came down in buckets. There was no flying and all we could do was to spend the days in our hotel, eating, drinking and watching Spanish bullfights on the telly. Eventually the weather cleared, we returned to the airport and found our Partenavia firmly tied down as we had left it so I proceeded with a thorough pre-flight check. Everything appeared O.K. and on checking the fuel, the tanks were still full as we had left them. A mere drop or two of water was spotted in the sight glass as I drew off a sample from each tank to check it. Once again the flight progressed without incident and on return, as usual the "Gazoline Senor" appeared with his little tanker of Avgas to fill up our tanks which he did - and as usual the amount we uploaded agreed with the number of hours we had been airborne.
The following day, the exercise was repeated: I checked the aircraft as usual, the tanks were full, the oil levels were correct and I proceeded to take the fuel samples. The starboard tank produced a few drops of water which failed to appear on the second sample so I walked around to the port tank. I filled the sight glass and was delighted to notice no evidence of any water droplets at all - well it had been a pleasant evening and warm night.
I was just about to discard the sample onto the tarmac when a thought occurred to me: How do I know that the sample is indeed avgas? I smelt it and it smelt faintly of petrol. I discarded it and took another sample - once again totally clear. Once again I smelt the sample - faint avgas wiff, then I thought - if I pour it over my hand it will rapidly evaporate and chill my palm. I poured, my palm got colder, but I was a little mystified by the tiny bubbles which appeared, drifting across my palm. I took another sample - still clear, but was that avgas smell strong enough? I thought. I was in a bit of a quandry and had no idea why I was making such a fuss. Anyway I proceeded back to the starboard tank and took a further sample. On sniffing, the avgas smell was much stronger so I returned to the port tank drain and took yet another sample for comparison. I was sure the smell was not as strong and there were also those little bubbles which drifted across the palm of my hand when I poured the waste fuel over it. Why? I took yet another sample and was rewarded with the reason why: the sight glass was full of water droplets in the avgas which rapidly settled to the bottom giving me half a sample glass of water and half a glass of avgas. The smell of avgas was much stronger now and when I poured it over my hand the chilling sensation was much stronger. A couple more sample glass fulls and the avgas was running pure and uncontaminated - so we could go flying.
Clearly the rain previously had entered the tank and lain on the bottom. During the manoeuvring during the previous days flying this water had entered the drain chamber at the bottom of the tank (below the point at which fuel is taken off for the engine) and there was so much of it that mistaking it for fuel was quite an easy one to make. To this day I have no idea why I was so insistent on making all those extra checks but at least it enabled our survey trip to complete without incident.
Like so many others, I seem to have a guardian angel watching over me and that is not the only time he has helped during my flying career.
P.P.