Guys,

The reason it works is that the pick up is ALWAYS in the centre . A clunk compromises this and effectively just turns it into another tank ( just smaller) . Any air that is introduced into the tank will hug the outside of the tank and stay away from a centralized pickup . A clunk pickup flailing around could possibly move into the air zone . If you never burn into the air trap you can be sure that you'll never get air in the system from an unported main fuel tank clunk . People who see the sack in a UAT as a feature that will filter out air bubbles and suck to the end are missing the point that the airtrap fuel should be considered unusable . At the end of a flight I very rarely have more than a fifth of the airtrap filled with air .

As far as the filtering benefit of the UAT , I figure all the filtering that occurs before the fuel goes in the tank and before the engine is enough.

Marc