Trouble Priming Nacelle Tank Transfer Pump on 421B

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    We are having trouble getting the left nacelle tank transfer pump to work. We have tested the pump and it works fine. When we have fuel in the nacelle tank it won’t come on. We found that if the sump just outboard of the nacelle is drained until no fuel comes out the pump will work. Does anyone else have this problem? How did you cure this problem. On my old 414 I had to prime the pump on the ground otherwise it wouldn’t work at altitude. On this plane I can’t get it to prime on the ground unless we drain that sump.


    There are 2 systems, those with the tick tack pumps and those with a standard pump that does not like being run dry. Either way a weak pump can be a pain, I have had to prime many on the ground before getting to altitude or you could not transfer the fuel at all. I have found weak pumps account for most of the problem, transfer times are very different, with the strong pumps system taking 30 minutes or less, the tick tack sometimes over 60 minutes. The pressure switch for the 421C is a ripoff from Cessna, the 340 and 421B ones not so bad.

    Peter Danto
    Premiere-Aviation Inc.


    While we haven’t owned our B model for very long, we have flown it numerous times with the nacelle/locker tanks and haven’t had any problems other than line guys filling them up to much and losing the fuel out of the drain while on the ground.

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