This happened recently:
A Cessna 172 with a fuel-injected engine (Lycoming IO-360) made its first flight after an 100 h-inspection. On short final, the engine quit. The pilot completed the landing without problems, and tried to restart the engine on the runway without success. The aircraft was towed to the apron where the engine was successfully started. Extensive engine runs suggested no problems. On landing, the aircraft had about 10 gallons of fuel on board, reasonably evenly distributed between the tanks, and the fuel selector was in the BOTH position.
The shop suspected that the engine had lost fuel and spent a day inspecting the fuel system for leaks and blockages without finding anything.
The pilot had made a final approach with low power, i.e. with a marked nose-low attitude. He extended full flaps on short final. Speculation was that the nose-down attitude combined with the deceleration on flap extension caused the relatively low amount of fuel to move forward leading to unporting in both tanks.
The C172 POH has lots of warnings about having the fuel selector on LEFT or RIGHT in low fuel situations, but nothing when the selector is on BOTH.
What do you make of this? 10 gallons is more than an hour’s flight time, so it would not be unexpected to land with that amount.
The fact that the engine could not be restarted on the runway but did successfully start when towed back to the apron, without anything else having been done, strongly suggests a vapour lock. There are multiple mentions of vapour lock on IO-360 on the web, too.
Would tuning on the boost pump imidiately fix a potential vapour lock?
pmh wrote:
Would tuning on the boost pump imidiately fix a potential vapour lock?
Yes and that is typically one of the first items on the engine out checklist
Ultranomad wrote:
The fact that the engine could not be restarted on the runway but did successfully start when towed back to the apron, without anything else having been done, strongly suggests a vapour lock. There are multiple mentions of vapour lock on IO-360 on the web, too.
Possibly. But the temperature was not unusually high (20°C) and the altitude near sea level. The aircraft does not have a history of vapour lock happening even at high altitude.
With the fuel-injected engine it’s probably a newer Cessna; I regularly fly a 175 with 9 USG unusable fuel. I would expect fuel issues at high/low pitch attitudes when using unusable fuel (not suggesting I would ever try this!). But you can probably rule this out, as the plane in question most probably had x USG unusable + 10 USG usable.
