After a long and high flight at 6000 feet with a glider, the last before re-fuelling, I did the usual slow spiral to retract the towing rope. I usually do it at 75-80 mph, any faster and the aerodynamic drag on the rope becomes to large for the winch motor. The mixture is leaned and carb heat is on. The descent is rather fast and the RPM is 1500-2000. When the rope was fully retracted I pushed the mixture and throttle wfd and headed for downwind 25. No reaction from the engine. Checked mixture, magnetos etc, but nothing. The engine was windmilling. I then radioed mayday, explained my situation, and continued towards downwind 25. I remember I was thinking about the surreality of the situation, "this isn't happening to me". But it was :-( I mean, that's the kind of thoughts one has before something is happening, not while it is happening :-) Even when training for emergency landings, I never really thought it would actually happen. And if it would happen, I surely would make a good landing :-)
I was high, about 4500 feet, the field is at 1800 feet. I thought initially I had lots of height for 25, but the descent with the wind-milling 4 blade propeller was huge. I don't remember looking at the VSI, but as I came on the downwind leg just before the level of the threshold at 07, I saw that the safer option was turning to final 07 and perhaps take a 360 to lose height instead of betting on the L/D ratio. At 4500 feet I couldn't really judge the L/D ratio, but it became increasingly obvious the lower I got. The L/D was in the brick league. So I turned to final 07 for a tailwind (10 knots) landing. I was too high at that point, but way to low to make a 360. I crossed the extended centerline, did a 150 degree turn around towards 07 from the north. At final I applied full flaps and sideslipped down. I landed about 1/3 into the field, rolled along and managed to turn into the taxi strip to stop.
I got all kinds of honors from the glider pilots for an excellent off engine landing, which was nice. Then we started thinking about what was wrong with the engine. Statistically the number one source of engine failure is fuel starvation. We checked the tank, and surely, it was completely empty. Ugh.
How could this happen? Our Pawnee has a history of running out of fuel, it has happened twice before. The last time with some damage. Our routine is to fill full tank after 10 launches. Looking at the log, the total feet of towing gliders, I should use about 98 litres for the last 10 flights based on our statistics for fuel consumption per towed altitude feet. I had to check, filled up the tank, and at 97 litres it was full. The problem with this is the tank on the Pawnee is 140 litres. What has happened to the last 40+ litres?
When I got home I filed (the mandatory) files to the Norwegian aviation authorities. The gliding club had also contacted the authorities, and a mechanic was sent to check the tank. The end of the story is that the Pawnee has a fiberglass tank with a plastic/rubber liner. When filling the tank full, it only takes about 100 litres. Then waiting for half an hour, and the liner stretches and additional 20-30 litres can be filled, but never the full 140 litres as per the book. The factory was contacted. Piper sold all rights to Laviasa in Argentina. They could tell us the producer of the tank/liner has no life limitation on the tank, but they (Laviasa) recommends changing the tank after 5 years. The reason is the plastic/rubber liner ages and gets less elastic over the years. I wonder how old our tank is: 30 years, 40? How many other old Pawnees are flying with variable volume way overdue tanks? Our tank will surely be replaced.
Things happens. I never ever thought I would actually run out of fuel in mid air, which I previously considered to be caused only by pure recklessness, but I did. I have never thought it would be physically possible that a full tank is not a full tank, only 70% full. But now I have experienced it first hand. On the other hand, I have always thought I would stay cool and make a perfect emergency landing, and I did :-)
I was of course extremely lucky. The engine could just as easily stop right after take-off, and then I would have to continue into trees, and could easily have been killed. Even worse, far into the mountains at Oppdal where the last flight went, and no easy access for rescue. Luck aside, I am happy with how I managed to positively fly the aircraft, take the right decisions as things progressed, and land without a scratch of any kind. I can thank training and experience for that. One of my old instructors teached me to visualize and think how to do cross wind landings. For instance whenever I had a free moment I should think how to apply stick and rudder in my head for different situations. That works, and I have also done the same exercise for other situations, like engine failure for instance. I guess it is a matter of being mentally (almost subconsciously) prepared for different generic situations, no matter how unlikely those situations seem to be. I guess this is a good experience to have before my first flight in the RV-4, but I hope it will never happen again, I can't be this lucky every time.
Edit: The tank has now been more thoroughly checked and it turns out the liner is held in place at the roof with 8 or 10 click buttons. None of these were in place, the liner was only hanging in there due to the fittings around the filler cap. It also looks like a wrong liner was installed, the buttons didn't line up correct.
