Pat Hatch's PhotoJournal A blog about photography & other musings…

Fire in Flight – Page 14.

At some point, the USAF or DoD began to add Explosion Suppresant Foam (ESF) to the fuel tanks of the C-130 aircraft, perhaps as a result (in part) of our shootdown and the B model loss a year later.  I'm not sure exactly when this started, but I do know that the H models, beginning around 1984 or 1985, were manufactured with the blue foam included, and the total volume of fuel went from 9,680 gals. to 9,248 gals., a reduction of about 4.5%, which you would expect.

Fig. 28 - This is either the #3 or #4 prop that was lost as the right wing contacted the runway.  Aircraft in the background.

Fig. 27 - This is either the #3 or #4 prop that was lost as the right wing contacted the runway. Aircraft in the background.

During the Iraq war, a British C-130 was shot down near Baghdad on 30 January 2005.  All 10 on board perished.  The aircraft was hit at low altitude, its right wing caught on fire and subsequently exploded.  Following is an exerpt from the UK Ministry of Defense (MOD) report on the incident:

"This explosion caused the outboard section of the wing to separate from the rest of the wing at which point the aircraft immediately became uncontrollable."

Later in the report, while discussing probable causes:

"The lack of fuel tank fire inerting system may have contributed to the loss of the aircraft.  We are now exploring the procurement and fitting of a suitable fire inerting system as a matter of urgency."

And from Air Chief Marshall Sir Jock Stirrup, head of the Royal Air Force, "It is clear that the aircraft was shot down by hostile fire.  The crew did all they should, and all that we would expect of such brave and professional airmen.  But they faced a combination of circumstances that, alas, no one could overcome."

Fig. 29 - Broken off blade from either #3 or #4 prop.

Fig. 28 - Broken off blade from either #3 or #4 prop.

It is my understanding that only one aircraft in the British C-130 fleet had the ESF installed at the time. I would expect that they all have it now.

So the question remains, does the blue foam only prevent an explosion or does it also prevent or mitigate a fire in the tank?  We know that fuel vapor explodes when ignited, but if you can displace the air in the tank ullage (the space above the fuel), by either inserting the foam or pumping in an inert gas, you can eliminate the danger of an explosion.  What about a fire?  I think a fuel fire is a product of an ignition source (e.g., an incendiary round) and a source of fuel vapor.  So, first the tank has to be ruptured; the fuel spilling from the rupture must then come in contact with the ignition source.  To the extent that the foam limits the spillage, perhaps it also mitigates the fire.  It is important to remember that it is not the fuel that burns, it's the fuel vapor.

It has been suggested to me that perhaps our wing fire was actually a hydraulic-fluid fire (MIL-5606).  That perhaps a flap actuator or its plumbing was hit, and the 5606, which is highly flammable, caught on fire.  This may very well have been the case, initially.  But, if so, it spread quickly to the fuel that had apparently been spilling from a wing tank rupture.  I would expect that just a few gallons of 5606 would have been present, not nearly enough to have sustained such a fire as we had.

There have been many instances in Vietnam where rounds penetrated fuel tanks on the C-130.  This happened to a member of my own crew, and they were able to fly the aircraft home with fuel pouring out of the hole.

So what happens when an incendiary round penetrates a fuel tank without the blue foam present?  My guess is that, if there is fuel vapor above the fuel, it would explode.  If the tank were full, the chance of an explosion is lessened, but perhaps you would have a fire at the point where the spilling fuel vaporizes and comes in contact with the entry point of the round.  On a tank with the foam present, the fire would be somewhat limited because one of the purposes of the foam is to prevent sloshage (if I can coin a word), in other words, the tendency for fuel to slosh or move about the tank.  This property would presumably limit the rate of leakage or spillage of the fuel, much like a sponge soaks up water.

I think it is safe to say that ESF is well worth its added weight and cost--and the 4.5% volume penalty--when weighed against the benefits of its added fire and explosion suppression, especially in the combat environment.

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  1. It is reasonable that the hydraulic system in the left wing could have contributed to the fire. That being said the only hydraulic lines in the left wing are lines associated with #1 & #2 pump which are the utility system pumps. The flaps are a jack screw, it’s hydraulic components which are primarily a brake and motor are mounted inside the cargo area, left rear of the wing box. Similarly the ailerons are controlled by a boost pack in the cargo compartment. The boost pack is connected to mechanical linkage that actually moves the ailerons. If it was hydraulic oil burning in may have come from lines in the #1 & #2 dry bays or plumbing between them and the fuselage. Regardless great job in bringing your crew home safe.

  2. Pat–congratulations on an outstanding piece of extended airmanship and leadership! As a two tour SEA pilot (A-1 Skyraiders and F-4 Phantoms), I particularly appreciated your words here about the benefits of fire retardant foam in fuel tanks. In my experience, that saved many birds and aviators. Since the Skyraider was a Korean vintage prop fighter, it had many,many retrofits. The three most significant were the Stanley Yankee Extraction System (a super ejection seat), thick armor plate around and under the cockpit, an retardant foam in the internal fuselage fuel tank. Quick supporting war story: in Northern Laos supporting General Vang Pao’s forces against a major NVA armored assault on Lima Site 20 Alternate, I took a .51 cal tracer round thru the fuselage fuel tank three feet behind me in the cockpit. The burning tracer entered the underside of the fuselage, and exited the top, passing clear thru the fuel tank. Remember that this was 115/145 AV gas, WAY more volatile than JP-4 jet fuel. The sensation in my “seat” was a muffled explosion “above me”, then nothing but normal flight. My wingman, some 1000 feet in trail at 400′ AGL, saw something very different. In an instant, my airplane disappeared in a large fireball, and an eternity later, simply flew out of the flash and smoke as if nothing happened. Another round in the right gear well got the utility hydraulic lines, so the return one hour flight to NKP was highlighted by many calculations about whether the AV gas leak rate out the bottom of the airplane would allow me to get home before “empty”, and whether the rarely used emergency gear lowering system would in fact work. All went well, gear came down, smooth approach end arresting cable engagement (no brakes), and the bird was towed in. On inspection, the .51 cal exit hole on the top of the fuselage was ringed with black fire residue. As observed by Gene Bardahl, my wingman, the still-burning tracer round passed through the entire foam-protected fuel tank without causing an explosion, exited the plane surrounded by a mist of AV gas, and promptly caused that fuel-air mix to explode above the fuselage. Thus my “big thump”, and Gene’s “large bright fireball”. Bottom line–LOVE those foamed fuel tanks when people are shooting at you!

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