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Lockable Gascolator Drain

UK CAA have just issued a helpful reminder about the hazards of Lockable Gascolator Drains.

They stress the lockable bayonet style drain as being the culprit, but when this happened to me the bayonet was not the whole problem. The gascolator drain on my -161 had been slow to drain fuel for a while, and referred to engineers a couple of times. It had to be pushed hard to get any fuel at all. Eventually it led to a sudden total power loss at 50’ with fortunately just enough runway remaining to land ahead.

What had happened was that it had become contaminated with – something – that had blocked the fuel from draining. Pushing hard had engaged the bayonet. This wasn’t noticed (by me, at the time) because no fuel ran out after fuel sampling, having obtained just enough fuel to check for water. Clearly the action of the fuel pump at takeoff had created just enough suction to draw in whatever the contamination was, and allow air into the fuel system. After taxing in it was pointed out that fuel was pouring from the now clear drainer.

A couple of subsidiary points – I can remember the stall warner blaring all the way back to the runway, and the engine bursting back to life the moment the wheels touched. The engine failure drill about closing the throttle is spot on. Nowadays, I always pull the drainer closed against the stops, not just check that it’s stopped dribbling.

Life lessons: 1) Don’t get fobbed off by engineers. It’s your neck. Same applies to engines that don’t like to start – this one got set on fire by someone else with a homemade starting technique because the engineers couldn’t be asked to find out what was really wrong with it. 2) Is fuel sampling in a PA-28 really a good idea? In 20 years I’ve never had the slightest trace of water, and provided you maintain the fuel caps, I don’t see how you could get water in the tanks, even living in the world’s worst climate. (I don’t subscribe to condensation theories, because it doesn’t happen in my collection of old cars, and water from the pumps? Who checks after every refuelling?). Despite all that, I still check the drains, but every time I do it I think about that day long ago.

EGBW / KPRC, United Kingdom

Interesting timing. We have three lockable drains on our aircraft. One of them has recently started to become sticky and prone to staying slightly open with a dribble. I have it on the list to get changed next week.

United Kingdom

We have one lockable drain (on the bottom of the aux tank). Without an aux tank, an Auster has no drain you can check at all! (There is a fuel screen, but you have to cut safety wire and remove the bottom of the bowl to check it, we check and clean this every 6 months and I’ve never found more than a couple of grains of sand in the bottom of the bowl).

In any case, I’ve never found any contaminants from our aux tank drain, which is the lowest point in the fuel system. I disassembled the fuel system last annual to replace some expired parts (seals etc) and while removing the fitting out of the bottom of the main tank got a good couple of litres of fuel out (the unusable fuel) which also had no kind of contamination. There’s a finger screen on the main tank fitting, so there’s two screens by the time you get to the engine – I have to imagine this arrangement is fairly common.

Andreas IOM

Thank you for your recount.

Pushing hard had engaged the bayonet.

In other words, it remained open?

Freelance IRI / CB-IR Instructor
LOWG | Worldwide

My new club has several amateur built Jodels. None of them have any fuel drain. They never had issues.


Snoopy wrote:

Pushing hard had engaged the bayonet.

In other words, it remained open?

Yes. Normally I would just push it sufficiently to get a couple of cc’s of fuel being well aware of the pesky locking problem. This time, I’d pushed it hard enough to engage the bayonet without realising it because only a few drops of few came out, and then stopped.

EGBW / KPRC, United Kingdom

Aveling wrote:

In 20 years I’ve never had the slightest trace of water

I’ve been flying for about as long as you, and I’ve found water maybe 2-3 times. One of them was after the aircraft had been parked outside during a full day rainstorm, but the other must have been condensation.

ESKC (Uppsala/Sundbro), Sweden

Airborne_Again wrote:

the other must have been condensation

How much water from condensation did you sump? I’m still to find any water, luckily.

EPKP - Kraków, Poland

tmo wrote:

How much water from condensation did you sump?

Can’t remember now. I have a photo around somewhere – will try to find it.

ESKC (Uppsala/Sundbro), Sweden

I recall a requirement/recommendation to modify lockable drains to remove the locking tabs so as to make them unlockable due to similar incidents in the uk?
I have found significant(engine spluttering) amounts of water when sumping some aircraft over the years…almost certainly due to outside storage with leaky fuel caps.

Last Edited by PeteD at 24 Feb 09:42
EGNS, Other
11 Posts
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