I no longer change tanks immediately before take-off – because, IF there was a blockage, the engine would stop after lift-off. I’d rather have that happen when I change tanks at about 1000’. (I’ve had a partial finger-filter blockage, in the rear tank which is not used at take-off.)
I guess that is true, I wanted to find an argument against that, but as has been pointed out, an aircraft might well run for a good few minutes on whatever was previously in the system, so actually what is a change of fuel tanks proving in a relatively short power check, and almost immediate departure? Hmmmm….
The early TBs had the fuel selector behind the yoke.
The later ones have it on the centre console, above the fuel filter.
The procedure is to taxi out on the less full tank, and at the holding point swap to the fuller tank, then do the power checks.
The procedure is to taxi out on the less full tank, and at the holding point swap to the fuller tank, then do the power checks
Sure, that’s what I do as well, but say there was an unbeknown to you problem with the fuller fuel tank, you have taxied out on the lesser full tank, you switch and do your power checks and you are using whatever fuel is still in the system from the less full tank, you line up and take off, then splutter and its a dead engine? Maybe this couldn’t happen, hence my probing, and I guess it depends on how much fuel is ‘in the system’ and whether in reality it would all get used up during a power check and the problem would never occur. But Maoraigh doesn’t think that.
Easy way to check for your aircraft is when at idle just before power checks turn off fuel and time how long engine takes to stop, that it time fuel in the lines will take before it would draw new fuel from a changed tank
I check the electric pump before startup (aurally and with the fuel pressure gauge) and then shut it off. Then I taxi out on the mechanical pump and monitor fuel pressure. I then run up on the electric pump, monitoring fuel pressure, and take off. All that is done on the same tank. After takeoff I switch tanks and monitor fuel pressure, then turn off the electric pump and monitor fuel pressure.
Also FWIW I stopped running tanks dry in the air after I inadvertently did it on the ground once, quickly turned the fuel on again before the engine quit, and the inrush of fuel to the carb float bowl jammed the float valve closed. Two minutes later the engine quit while taxiing and didn’t restart until the float was knocked loose by tapping on the carb. A boost pump might have pushed the float valve open, but this was a gravity feed system with no pump.
Sure, that’s what I do as well, but say there was an unbeknown to you problem with the fuller fuel tank, you have taxied out on the lesser full tank, you switch and do your power checks and you are using whatever fuel is still in the system from the less full tank, you line up and take off, then splutter and its a dead engine?
This happened to a Piper Tomahawk at Barton in 2011. Big fiery crash, 1 dead, one seriously injured although the outcome may have been better had the aircraft not been stalled.
http://www.aaib.gov.uk/cms_resources.cfm?file=/Piper%20PA-38-112%20Tomahawk%20G-RVRF%2004-12.pdf
There is no way to guard against a problem like that, is there?
The only way to know all the fuel in a tank is available is to, ahem, burn it all in the engine 
The problem is that in the spamcan scene (and a Tomahawk qualifies for that, with every one I have ever flown in having been in the most appalling condition) you have fuel gauges which range from poor to completely useless, and if you throw in forgetting the physical fuel level check (or being told by the school to not worry about it) you have it….
I recall draining out some litres of water out of a Tomahawk, preflight, and that might have been an engine failure just after takeoff. Perished filler cap seals.
This happened to a Piper Tomahawk at Barton in 2011. Big fiery crash, 1 dead, one seriously injured although the outcome may have been better had the aircraft not been stalled.
Thats interesting, it looked like plot error as the report did say that the fuel selector was likely in between L and R tanks. Whether this was an accident, or if the rod had slippped wasnt concluded. It also suggests for a tomahawk, that an engine will run for 30 seconds before it is starved of fuel as a result of a incorrect tank selection, but that the ‘inbetween’ tanks had caused the engine to run longer than that before stopping.
What I take from this is that:
- You should change tanks during power checks.
- As Balliol suggested, find out for your aircraft how long it will run with fuel already in the system before it quite.
- Make sure your fuel selector is firmly in the L or R position.
you have fuel gauges which range from poor to completely useless
This seems to be more common than not. What I do with an aircraft I’m unfamiliar with is that I trust whatever tells me I have the least fuel – if my fuel burn calculations gives the less optimistic number I go with that, if the fuel gauges show less than my calculation, I trust the gauge. One time in a C182 (an older one without the rear windows, but in very nice condition, which was in our flying club in Houston) which I had only just got checked out in, although I had visually checked the tanks before leaving about halfway through the flight the fuel gauges were showing a bit less than what my fuel burn figures said, so I canceled IFR and landed before my intended destination to check the situation out. It turns out when that model’s tanks look full there’s still about 10 US gallons you can get into the tanks to make them really actually full. Good job I checked too, since the planned flight left me with 1 hour remaining in the tanks at my destination, and a 10 gallon discrepancy meant I would have actually arrived with very little remaining (certainly little enough that a missed approach could have been a big deal).
if my fuel burn calculations gives the less optimistic number I go with that, if the fuel gauges show less than my calculation, I trust the gauge
The problem with that is that if the gauge under-reads and thus forces you to make a descent for a refuel, through hazardous weather or among hazardous terrain, you have increased the risk profile of your flight.
IMHO the correct procedure is to disregard a dodgy fuel gauge completely, and install a fuel totaliser
But even then a totaliser isn’t going to tell you about a fuel system leak before the transducer… so one really needs both systems to work right.
