Wing Locker Vent – 421B

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  • #83903

    After my client purchased a new to us 421B, we got it home and are getting ready to put it into service. It has the long range tanks (dual wing lockers) and I had the local FBO top it off today. I went out to the airport about 30-45 minutes later to find a huge pool of 100LL on the ground and a steady stream coming from the right wing locker vent line (think water hose…not a simple drip). I have had similar incidents in other aircraft, and upon immediately opening the fuel cap in the locker tank, hear a huge WHOOSH of air, and viola, the stream of fuel out the vent/drain line stops.

    In studying the fuel schematic, it looks like the wing locker tank fuel cap is not vented, although I am not 100% sure. Anyone know how this little error could have occurred and a way to keep it from happening in the future? Since there are no fuel gauges on the locker tanks, it would be a real bummer to have to terminate a flight early due to the fuel getting sucked out of that tank and not being where I needed it to be.

    Thanks!

    #96861
    quote ZARMSTRONG:

    After my client purchased a new to us 421B, we got it home and are getting ready to put it into service. It has the long range tanks (dual wing lockers) and I had the local FBO top it off today. I went out to the airport about 30-45 minutes later to find a huge pool of 100LL on the ground and a steady stream coming from the right wing locker vent line (think water hose…not a simple drip). I have had similar incidents in other aircraft, and upon immediately opening the fuel cap in the locker tank, hear a huge WHOOSH of air, and viola, the stream of fuel out the vent/drain line stops.

    In studying the fuel schematic, it looks like the wing locker tank fuel cap is not vented, although I am not 100% sure. Anyone know how this little error could have occurred and a way to keep it from happening in the future? Since there are no fuel gauges on the locker tanks, it would be a real bummer to have to terminate a flight early due to the fuel getting sucked out of that tank and not being where I needed it to be.

    Thanks!

    I don’t think that cap is vented. If they filled it high, and it heated up, it would displace all the air in the tank. It will siphon since the vent line entrance is at the very top and the exit is lower than the tank. Since it is a soft sided fuel cell it will suck in as the fuel siphon’s out. I could easily see gallons lost.

    Your best bet is to fill it up right before you use it, or to only put 25 gallons in it to allow some room for expansion.

    Eric

    #96863

    Thanks!

    #96864

    I forgot to mention that if the tank is leaking near the wing locker drain valve, or anywhere aft of the fuel cell and inboard of the nacelle it is almost certainly a problem with the tank itself, or the hose from the tank. Something to think about when you open the luggage door and it turns on the always powered light via a micro switch….

    This is not the problem for this 421B, but something to keep in mind in general. 🙂

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