Single vs Double flared tubing

Do aluminum aircraft fuel lines need to be double flared for AN fittings (37
degree flaring)? There is a significant difference in cost between a single
and double flaring tool. I ran across this in Car Craft magazine:

"Most tubing in the aircraft industry is extruded in one piece with no seam,
so double flares aren't required to prevent crack formation."

"Craig Foster" wrote in message
news:BtFKc.126936$Oq2.10649@attbi_s52...
Do aluminum aircraft fuel lines need to be double flared for AN fittings
(37
degree flaring)? There is a significant difference in cost between a
single
and double flaring tool. I ran across this in Car Craft magazine:

"Most tubing in the aircraft industry is extruded in one piece with no
seam,
so double flares aren't required to prevent crack formation."

The Parker flaring tool we use here makes burnished, deburred 37 degree
single flares in aluminum tubing used for fuel and hydraulic lines. It is
easy to use and quite precise.

I have made double flares with an SAE 45 degree tool and copper tube, which
is legal for some fuel lines on old airplanes like Cubs and Taylorcrafts.
The flares are pretty, hell on the forearm tendons when you're making them,
and hold up well, but are unnecessary.

I have heard of double-flare 37 degree flaring tools but never used one.

I have seen kits for complex airplanes with compression fittings for the
hydraulic lines. Whenever an A&P sees them he usually begins to slobber
like Pavlov's dog. Except the sentiment is not hunger, but anger.