Robert Moore wrote in
46.128:

Big John wrote
Before the Airlines started flying jets the Air Force ran into a fuel
problem in their jets at altitude. Can't remember now if it was ice
xtyls forming in the fuel or waxing as you say but the Air Force
started putting an additive in their fuel that stopped that problem
and the Airlines picked up on it when they started flying jets I was
told.

I flew the first generation jets (B-707) for the first major operator,
PanAm. There was nothing in our manuals about a fuel additive being
used,and we bought fuel all over the world. We used bleed air to deice
the fuel filter. One minute ON every thirty minutes if Tank temp was
below zero degrees centigrade or one minute ON if any icing light
illuminated.

However, if the tank temp dropped below three degrees centigrade above
the freeze point of the particular fuel on board, the pilot was
required
to take one of the following actions:

1. Increase IAS to warm up the wing.
2. Descend to a warmer cruise altitude.
3 Reroute to a more southernly route.

The basic problem was that the xtyls would form in the fuel and then
pack the filter and stop fuel flow.

The fuel filter was located between the first and second stages of the
fuel pump. Any blockage of the filter opened a bypass around the fuel
filter. So....a blocked filter would NOT stop the fuel flow. Actually,
there were two bypasses, one as just described and a second one around
both the pump first stage and the filter.

I would strongly suspect that Boeing still provides at least this same
level of protection for its current generation of jetliners.

Nope. And I have no idea why. The A300 didn't have one either.
There's certainly no control for it in the flight deck, and if there was
an automatic syste, they would have had to have told us about it since a
malfunction would mean an insanely high oil temp. ( I had three
shutdowns in 727s due to fuel heat getting stuck on)

Do the Airlines still use the/a additive in their fuel for the high
altitude problem?

Never did as far as I know. The corporate guys do add Prist, probably
due to the much thinner wings.


Yeah, I've never seen it added to an airliner's fuel either. I've a
vague recollecton of seeing prist added to a lear's fuel with a special
fitting on the fuel hose accepting a can of prist. But AFAIK we don't
have anything.


Bertie