From: phoebus@iinet.net.au
Sent: Sunday, September 10, 2017 12:09 PM
To: 'editor@aviationfirejournal.com' <editor@aviationfirejournal.com>
Subject: Suggested Article Topic

to: editor aviationfirejournal

Many (if not most) supplementary oxygen-related (or -initiated)  fires occur on the ground during replenishment or systems maint, however some are just as likely to occur in the air and pose unique problems for flight crews (as well as accident investigators).

Because supplementary oxygen systems often have only their HP ON/OFF cocks remoted at the bottles, and no alternate way of restricting or removing flows to a HP oxy-leak, it’s always unlikely that a flight crew will have time to identify such a fire as being oxygen-related - and get to isolate that bottle supply in time. The time available factor is going to be very different to a smelly “fire of unknown origin” emanating from a Swissair 111 type scenario of a wiring-initiated fire.

Once an oxygen fire takes hold, it will have some very unique properties – and the airborne pressurized variant will be entirely different to that same cause fire arising in an aircraft on the ramp. Due to oxygen enrichment levels being related to detected (or undetectable) leaks inside a virtually hermetically-sealed flight-deck airborne, its aerial flashover characteristics in a pressurized fuselage can also be restricted to being very particular to this genre of accident scenarios.  Tell-tale signs for crash investigators may be the extent to which the plastics technology found in the modern flight deck has been affected (LED screens, switches, solenoid holds, switch surrounds, circuit-breaker trips, crazing of transparencies, surface effects on differing plastic types on consoles, seats etc). Shielding by pilots’ bodies and seat structures and directionality of flame-front propagation might also allow discrimination of a point source.

As per many oxygen ground fires, the distinctive signature of a fuselage burn-through seems to presage the next destined development in an airborne oxygen fire scenario…. i.e. that of rapid depressurization. One must then reflect upon the consequent conundrum for the pilots. In any other depressurization scenario, the pilots are 100% reliant upon 100% oxygen and an emergency descent as being the safe extrication from their predicament. This is not so in an airborne supplementary oxygen fire that leads to a hull rupture. But, due to their oxygen's involvement, that conclusion is admittedly dependent upon a number of other factors. But it's very likely that their life-saving oxygen supply will be cut off by any oxygen leak and/or fire. So, as Shakespeare said: "...and therein lies the rub".

But then a normally unasked question pokes its head up. “What happens to an oxygen fire on the flight-deck once a point-source oxygen fire, supported by the ballooning outwards pressures of pressurization, causes a fuselage rupture?” Obviously that fire will be quenched almost immediately. But did the flash-over cause sufficient damage to systems to cause a subsequent crash? Or could the aircraft fly onwards until fuel exhaustion (per MH370)?

Deficient design characteristics of oxy systems have been identified in accidents over the years, even in modern aircraft. NASA maintains a whole unit dedicated to cataloguing oxygen fire related accidents and incidents. For instance the Canadian TSB found that aluminum HP oxygen lines with a low melting point were a factor in SR-111 (whereas high melting-point stainless steel is the minimum spec for oxygen lines). Investigators in other accidents have commented that, due to rubber-lined stand-offs, many aircraft don’t have any earthing of oxygen lines between the bottles and the distant overpressure burst discs on the fuselage side. Proximity of lines to electrical wiring and even tie-offs of electrical wire bundles to HP oxygen lines have featured in many other accident reports (e.g. 767 ramp fire destruction at San Francisco Intl ).

However because there have been numerous ramp fires emanating from oxygen systems that tend not to arouse much interest (because instant evacuation has always been the solution), it is always necessary to extrapolate the circumstance into the aerial variant – and to comprehensively entertain the differences in terms of complications and likely outcomes.

If you would like to read further into these MH370 prognostications see:

a.      Executive Summary:     at    http://tinyurl.com/gqpnwcn

b.      “MH370 (Not really a Mystery)”  at  http://tinyurl.com/or9bzf2

Accident: ABX Air Cargo B762 at San Francisco on Jun 28th 2008, on fire while parked, no arson   By Simon Hradecky, created Tuesday, Jun 30th 2009 18:25Z, last updated Wednesday, Jul 1st 2009 06:47Z   The NTSB reported in a press release, that the cause of the fire was a short circuit to the supplemental oxygen system, that reached the oxygen hose. The design of the hose included an internal spring, which could be heated by the inadvertent application of electrical current, causing the plastic hose to ignite. The coil acted as ignition source, the hose material acted as fuel and the oxygen promoted the fire. Boeing had already identified the safety issues involving conductive hoses and had issued a service bulletin advising operators to replace conductive with non-conductive hoses. The FAA approved the bulletin, but did not issue an airworthiness directive. The NTSB found that in other ABX Boeing 767 aircraft insufficient separation existed between wiring and oxygen system tubing, too. The NTSB issued a safety recommendation to require operators to replace electrically conductive with electrically non-conductive oxygen hoses. During the investigation the NTSB found, that the reading lights located in the passenger service units could become a potential source of ignition to nearby combustible materials. The NTSB therefore recommended, that all reading lights are to be mounted with rubber boots or other means to provide a greater level of electrical protection. The final report is to be expected in a couple of weeks. http://www.avherald.com/h?article=408ec81b/0005&opt=0   and   http://www.aircraftmechanic.org/showthread.php?1742-B-767-fire a.      Executive Summary:     at    http://tinyurl.com/gqpnwcn   b.      “MH370 (Not really a Mystery)”  at  http://tinyurl.com/or9bzf2   By Simon Hradecky, created Tuesday, Feb 23rd 2010 21:13Z, last updated Tuesday, Feb 23rd 2010 21:17Z   Stainless Steel Coil Spring Within Flexible Oxygen Hose  (Photo: NTSB)  The NTSB have released their final report concluding: The National Transportation Safety Board determines that the probable cause of this accident was the design of the supplemental oxygen system hoses and the lack of positive separation between electrical wiring and electrically conductive oxygen system components. The lack of positive separation allowed a short circuit to breach a combustible oxygen hose, release oxygen, and initiate a fire in the supernumerary compartment that rapidly spread to other areas. Contributing to this accident was the Federal Aviation Administration’s failure to require the installation of nonconductive oxygen hoses after the safety issue concerning conductive hoses was initially identified by Boeing. Following findings were listed by the NTSB: 1. The pop and hissing sounds heard by the flight crew immediately before the fire was discovered were consistent with the ignition of an oxygen hose by an internal rather than external heat source. 2. The design of the oxygen hose assembly allowed the internal spring to become a source of ignition when it was electrically energized, the polyvinyl chloride hose material to act as a fuel, and the oxygen within the hose to promote burning. 3. The fire aboard the ABX Air airplane most likely began when a combustible and electrically conductive oxygen hose in the supernumerary compartment became energized by a short circuit, which caused the hose to ignite and burn through, and the release of oxygen from the hose caused adjacent materials to ignite and burn at an accelerated rate. 4. Although no evidence was found to indicate that previous oxygen system leaks contributed directly to the fire in the supernumerary compartment, oxygen leaks are a safety hazard because of their potential to facilitate a fire. 5. Aircraft rescue and firefighting personnel extinguished the fire in a timely manner. 6. The skin-penetrating nozzle was an effective tool in extinguishing the fire, especially because the forward doors were rendered inoperable by the fire and could not be used to gain access to the fire. 7. The type of training that the driver of Rescue 49 received on the operation of the high-reach extendable turret with skin-penetrating nozzle was not sufficient to allow him to successfully insert extinguishing agent into the cockpit on his initial attempts. 8. Aircraft rescue and firefighting personnel who are not sufficiently trained on the high-reach extendable turret with skin-penetrating nozzle may not be able to use the device effectively when fighting aircraft fires. 9. Combustible oxygen hoses with an electrically nonconductive design would prevent the internal coil spring from becoming electrically energized, mitigating the possibility that the hoses would melt and ignite. 10. It is likely that the modifier of the accident airplane would have recognized the use of a part that was potentially combustible before releasing the airplane to the operator if the Federal Aviation Administration had issued an appliance airworthiness directive that cited the part manufacturer as well as the airplane model. 11. Protecting oxygen system tubing from inadvertent short circuits is important because of the proximity between the tubing and electrical wiring in a compressed area as well as the potential severity of a fire involving oxygen. 12. An effective method of electrically grounding the supplemental oxygen system to the airframe would help ensure that oxygen system components are protected from short circuits. 13. Because aging polyvinyl chloride flexible hoses are more likely than newer hoses to be cracked or otherwise degraded, aging hoses are more likely to leak oxygen, which, along with an ignition source, could result in a fire. 14. Passenger service unit reading lights with exposed electrical contacts have the potential to move to positions that create inadvertent short circuits and produce sparks near combustible materials. 15. Installing smoke detectors in supernumerary compartments would help flight crews identify the existence of a fire in an accessible, possibly unoccupied space and initiate suppression of the fire before it could propagate and become uncontrollable. 16. The number of reported discrepancies regarding the accident airplane’s oxygen system was excessive and indicative of a chronic problem with the system, yet ABX Air’s continuing analysis and surveillance program did not include adequate actions for resolving the discrepancies and preventing additional oxygen leaks from occurring. The crew was preparing for departure, all freight had been loaded, the doors were already closed, when the crew performed their oxygen check, which completed normally. About 6 minutes later the first officer went to the supernumerary compartment, located right behind the cockpit, to turn off the lights. At that time he did not notice anything abnormal. One minute later, when the crew was running the engine start checklist, they heard a loud pop followed by a hissing sound followed by the first officer noticing a big fire in the back. Subsequently the lavatory smoke detector activated and a fire bell sounded. The crew called ATC informing of a cargo fire, ground control confirmed to "roll the trucks", then the crew executed the fire and evacuation checklist. They could not exit through the L1 or R1 doors due to the location and intensity of the fire, so that both pilots evacuated through their cockpit windows. The first officer used his escape rope to climb down, then instructed ground personnel to move the stairs under the captain's window, so that the captain climbed down those stairs. Due to the extensive damage ABX Air confirmed the airplane to be a hull loss.   Oxygen System Components in Supernumerary Compartment (Photo: NTSB): Proximity of Electrical Wiring to Oxygen System Tubing (Photo: NTSB):     By Simon Hradecky, created Tuesday, Jul 22nd 2008 22:36Z, last updated Wednesday, Jul 1st 2009 06:42Z   "Maintenance in work" says a sign attached to the wall, that once separated the cockpit from the cabin, as the airplane was being prepared to be towed away from the stand, where it had caught fire. Heat and smoke caused severe damage not only to the fuselage, but also in the cockpit.   Smoke and heat damage in the cockpit, photo: Vlasta Sajfr   Location of fire, photo: Vlasta Sajfr     By Simon Hradecky, created Thursday, Jul 3rd 2008 20:17Z, last updated Wednesday, Jul 1st 2009 06:42Z   The National Transportation Safety Board reported today that ABX Air had received a threat against an unspecified aircraft within a week prior to the accident. The fire started immediately behind the cockpit outside the cargo hold. Cockpit Voice Recorder and Flight Data Recorder have already been sent to Washington for analysis. Both pilots have been interviewed yesterday. The NTSB is expected to conclude its on-scene investigations by July 6th.     By Simon Hradecky, created Sunday, Jun 29th 2008 07:01Z, last updated Wednesday, Jul 1st 2009 06:41Z   An ABX Air Boeing 767-200, registration N799AX preparing to perform freight flight GB1611 from San Francisco, CA to Wilmington, OH (KILN)(USA), was parked at the ramp, plot 11, with engines shut down to be loaded and fueled, when fire broke out immediately behind the cockpit. The two pilots were on board, one received minor injuries and was brought to hospital. The Air Mail facilities (including DHL and USPS) with more than 100 workers have been evacuated as well. Fire brigades reportedly had to cut a hole in the cockpit area to gain access. The fire was quickly contained. The airport reported that the airplane will be "unuseable for a while". Track of last GB1611 (June 21st): http://flightaware.com/live/flight/ABX1611/history/20080622/0517Z/KSFO/KILN More pictures are available at: Jack Hannen's KSFO Gallery (http://www.pbase.com/ksfo/burned_dhl_767_sfo)

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