Fuel drain leaking spontaneously?

[ArtVandelay]

Everything was normal, during preflight no issues. After a 4 hour flight I landed and the fuel drain was leaking? I am trying to figure out why. I wasn’t high enough to have freezing temperatures.

[Yetti]

Wing drain or colator drain?     Try exercising it.   Then replace it. Rubber seals get old and fail.

[EricJ]

Sometimes the sumps get a little chunk of debris in them.    Working it around with the drain cup probe will usually dislodge it.

[ArtVandelay]

Sometimes the sumps get a little chunk of debris in them.    Working it around with the drain cup probe will usually dislodge it.

Yeah, but I understand if that happens after using it during preflight, but how did this happen in flight?

[ArtVandelay]

Wing drain or colator drain?     Try exercising it.   Then replace it. Rubber seals get old and fail.

Wing drain, I did exercise it, took about 10-20 times to finally get it to stop.
It’s not that old, just a few years.
Find it odd that it did it in flight.

[MikeOH]

Not sure how 'bad' this leak was, but is it possible that it started to leak after you sumped the drain during pre-flight and you just didn't notice?

[Falcon Man]

Possible explanations: the leak was slow and not noticeable on preflight inspection; expansion and contraction of all components of the drain could allow more debris to settle in during the flight and lead to a more noticable leak. The most common debris culprit is flaking of the tank sealant which occurs whenever the wings flex in turbulence and upon landing. 

[ArtVandelay]

Not sure how 'bad' this leak was, but is it possible that it started to leak after you sumped the drain during pre-flight and you just didn't notice?

No way, it was leaking really bad, not just a drip.

[EricJ]

Was it leaking out the drain hole or around the outside of the nut?    It could be that it's working loose if it is leaking a lot.    You could try just tightening it up if it is leaking around the part rather than through the drain.  They're not hard to change, and if you're a little bit bold you don't even need to drain the tank.

[ArtVandelay]

Was it leaking out the drain hole or around the outside of the nut?    It could be that it's working loose if it is leaking a lot.    You could try just tightening it up if it is leaking around the part rather than through the drain.  They're not hard to change, and if you're a little bit bold you don't even need to drain the tank.

Through the drain hole, I put my finger to stop the flow.

I need to order a replacement/spare.

Is the fuel tank under pressure from airflow into the vent?

[Yetti]

48 minutes ago, EricJ said:

Was it leaking out the drain hole or around the outside of the nut?    It could be that it's working loose if it is leaking a lot.    You could try just tightening it up if it is leaking around the part rather than through the drain.  They're not hard to change, and if you're a little bit bold you don't even need to drain the tank.

gives a new meaning to hot swap.

[Ragsf15e]

1 hour ago, EricJ said:

Was it leaking out the drain hole or around the outside of the nut?    It could be that it's working loose if it is leaking a lot.    You could try just tightening it up if it is leaking around the part rather than through the drain.  They're not hard to change, and if you're a little bit bold you don't even need to drain the tank.

I had mine changed a few years ago, and you’re right, he just hot swapped them. Said he did it all the time.

[LANCECASPER]

I always carry a spare fuel drain just in case this happens during pre-flight.

[201Mooniac]

I've had several changed over the years, Top Gun never drains the tank and barely spills a few ounces of fuel.

[pwnel]

I have a story on this.  On my recent flight from Adak to Sapporro Japan, the same thing happened while pre-flighting in Adak.  I sumped the port wing, continued my walk around and noticed a large pool of liquid under the plane as I was busy on the starboard side.  Walked backed and the valve was leaking at a strong pee-level.  Almost had a heart attack as I had 1900nm to fly with no option for more fuel as I'd shipped my two drums of AvGas to Adak at great expense months ago and there weren't any more for a 1000 miles. Got the leak to stop by working the valve, just as mentioned here.  

Took off for Japan.  But now you're in the air with 14 hours to go.   And of course you start thinking - what if that leak came back.  Like the OP here describes.......... I swear I probably stared at that left tank fuel gauge for two hours non-stop before I convinced myself it's probably fine.  (it was).