On Sunday I was going to fly over to Bremerton from AWO, but I ended up getting some more important obligations the meant I would have to be back in Seattle around 1-2pm. After flying for 1.5 in the morning I found out that those plans had been canceled, so I installed some VGs that I had been wanting to test on the elevator, fueled up ( and yes, I tested the fuel at all three sumps ) and went back to flying.
My normal routine for testing out a change like this is to follow the valley and fields Northwest from AWO towards Stanwood and then try turns, stalls, ect at high altitude then return back to AWO to try landings and then more landings to make sure I like the change.
After about 54 minutes of trying out the VGs I hit a problem.
Halfway through a downwind leg at cruise power\attitude I hit an unexpected loss of power.
The engine became rough and power dropped down to an almost stopped state, then came back up gradually, went back down gradually a few seconds later, came back up gradually a few seconds later, went back down, came back up. The loss of power lasted about 45 seconds to a minute. Carb ice crossed my mind while doing the landing. It was similar to the symptoms of carb ice in an O-200, but my installation has constant carb-heat.
At the first sign of the drop I had already started pitching for glide and called out the mayday. There were two planes on final and one on base. The two on final went around, but the pilot in the tow-plane still turned final and did not abort, turn or otherwise react. Several other people on the radio chimed in in an effort to get him to react.
With the 701 I fly my downwind and base no more than ¼ mile out. I turned base just a little North of the numbers and landed the numbers with better than idle power.
Sadly the on board camera had run out of battery and 1) did not catch the engine event 2) did not catch the emergency landing with a HAPL approach that I hope would have made my flight adviser proud.
Up to that point I had put on 2.5 hours alone that day. There was plenty of fuel and I was hallway finished with my downwind at cruise power, so even a failed fuel pump should have not caused this.
After landing I did do a full run up, and everything was fine. It made full power, mags grounded, ect.
The loss-of-power event was caused by a clog that collected in the fuel filter. My morning preflight showed no issues at the gascolator or in the fuel filter. My theory is that debris that had not been swished out of the tanks, along with debris introduced by auto-fuel and some small amounts of sealant collected in the gascolator on the forward edge. Earlier in the morning I performed a test were I wanted to see how far I could taxi with the fuel valve shutoff ( this was due to several accidents this year were some Cessnas had enough fuel to start takeoff with the valve shutoff ). The intentional fuel starvation most likely caused suction in the fuel lines causing the clog to dislodge and move up the fuel line to the filter.
As a result I will be cleaning the filter and gascolator every 20 hours or so.
Video of a short landing:
Video of flap testing\very consistent landings: