Re: A second 757 crash -- off the Dominican coast

From:         shafer@ferhino.dfrc.nasa.gov (Mary Shafer)
Organization: NASA Dryden Flight Research Center, Edwards CA
Date:         15 Mar 96 01:05:22 
References:   1 2 3 4
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On 07 Mar 96 02:06:22 , mkrotz@enet.net (Mark Krotz) said:

M> There is actually an Airworthiness Directive out prohibiting the
M> use of JP4 in a number of turbine powered aircraft (including the
M> Boeing 737).  If I remember right, it has to do with the fuel
M> controls not liking the difference in specific gravity of the two
M> different fuels, which has actually resulted in in-flight
M> flameouts.  JP4 is still available as far as I know, and JetA is in
M> common use in most civil turbine aircraft.

JP-4 is no longer available, having been replaced with JP-8.  The only
way to get JP-4 is to have a special run done at the refinery.

A previous poster suggested that JP-5 was the successor to JP-4.  This
is incorrect.  JP-4 was used by the Air Force and was based on avgas.
This is quite volatile, with a fairly low flash point, and the Navy
did not consider it to be sufficiently safe for use on carriers.  The
Navy specified JP-5, based on kerosene, for its airplanes.  JP-5 is
much less volatile than JP-4 and has a much higher flash point.

Jet engines are not actually too terrible fussy about what they burn
(the seals, etc, may be, but the combustion process isn't) and Navy
aircraft could use JP-4 if JP-5 wasn't available, for instance at an
Air Force base.  However, the Navy required that the JP-4-fueled
airplane be refueled with JP-5 a number of times (4 or 5, as I recall)
before the airplane could be struck below to the hangar deck, which is
a confined space filled with fueled aircraft.

JP-8, the replacement for JP-4, is also a kerosene-based fuel, but
slightly more volatile than JP-5 and having a slightly lower flash
point.  However, it's much better than JP-4.  It has the added
advantage of being used by tanks, trucks, and other ground vehicles,
as well as helicopters.  Switching to it improved fuel safety and
reduced the number of fuels required from the military from three to
two.

There are still a few aircraft in use that won't run on JP-8 instead
of JP-4.  The one I have first-hand knowledge of is the
variable-stability NT-33A.  This plane will run, however, on a mixture
of avgas and oil, although this does coke the engine up a little
faster than JP-4 did.

Dryden discovered the difficulties with introducing JP-8 to a JP-4
airplane when we were flying the last few flights with our F-104Gs.
While the engines ran well, the seals on the nozzle actuators were
damaged by the JP-8 and had to be replaced with new ones.



--
Mary Shafer               NASA Dryden Flight Research Center, Edwards, CA
SR-71 Flying Qualities Lead Engineer     Of course I don't speak for NASA
shafer@ferhino.dfrc.nasa.gov                               DoD #362 KotFR
URL http://www.dfrc.nasa.gov/People/Shafer/mary.html