Time for Built-in Cockpit Fire Extinguishers

The cockpit of a modern jet gives the impression of the soul of rationality and safety. Glowing instrument displays, rows of softly illuminated knobs and dials.

What’s not evident to a boarding passenger passing by the open cockpit door is the absence of built-in fire detection and suppression. A search for the round disks found on the ceilings of office spaces — indicating the presence of built-in fire extinguishers, will be in vain. A close look will reveal that a small, hand-held extinguisher is located in the cockpit; it is a testament to futility, as there is no way to inject its chemical agent behind panels to get to where a fire is going to be found, adjacent to the miles of electrical cables and fittings. Chafed wire or, worse, the presence of electrical arcing in the vicinity of emergency oxygen lines can lead to extremely dangerous oxygen-stoked fires.

At least two sure fires in recent times illustrate the extreme danger. One such conflagration occurred in July 2011. An EgyptAir B777-200 experienced a ravaging cockpit fire while on the ground Cairo, before the airplane was to depart with passengers (307 occupants, passengers plus crew). The fire, started in an oxygen line, scorched the cockpit and blowtorched a hole in the fuselage. The fire was caused by an electrical short circuit to the helically wound internal stiffener wire that provided rigidity, preventing hose-kinking and flow restrictions leading to the first officer’s oxygen regulator. The stiffener wire unfortunately was electrically conductive.

From the Egyptian investigation, the fire-ravaged remains in the cockpit. The full report by the Egyptian Aircraft Accident Investigation Central Directorate may be viewed at www.skybrary.aero/bookshelf/books/2394.pdf

From the Egyptian investigation, the fire-ravaged remains in the cockpit. The full report by the Egyptian Aircraft Accident Investigation Central Directorate may be viewed at www.skybrary.aero/bookshelf/books/2394.pdf

From the Egyptian investigation, the burn-through of the aluminum skin

From the Egyptian investigation, the burn-through of the aluminum skin

Fueled by 100% oxygen in the pilots’ emergency supply conduits, the fire might be described as an “oxygen flare fire.”

Prior to the EgyptAir B777 fire, a nearly identical fire also occurred on the ramp at San Francisco in June 2008. The flight deck of the B767 cargo plane was covered in soot; gaping holes were torched in the fuselage (see www.ntsb.gov/investigations/AccidentReports/Reports/AAR0904.pdf).

The fire damaged ABX B767 at San Francisco

The fire damaged ABX B767 at San Francisco

If an oxygen flare fire occurred in the cockpit during flight, as opposed to on the ground, a hand-held extinguisher would be of little use; there is no way to direct the extinguishing agent at the base of the fire, which is behind panels and other surface coverings.

At altitude, an oxygen flare fire would feature instantly high temperatures, lowering quickly as the oxygen was consumed. Many electrical circuits and associated avionics would be destroyed by the heat’s effect on flare-exposed plastic push buttons, LED screens, keypads and other plastic components that have replaced metal fixtures in earlier generation cockpits.

The following justification to this scenario follows:

ItemDescriptionImplications
Oxygen flare fireInitiated by a wiring insulation flaw. Flare-up of 10-15 seconds duration (25-30 seconds at most) until oxygen depleted, hull rupture or leak blocked by melting material at the leak.Loss of the aircraft.
Effect on cockpit instruments, displays and flight controlsThe high heat of an oxygen-fed flare fire would melt/distort plastic switches and buttons in relation to their dissimilar plastic housings.Although modern aircraft feature multiple back-up redundancies, those redundancies would be compromised by melting plastic buttons and switches and/or their latching solenoids, and it is possible to kill individual systems.
Hull ruptureExplosive decompression due to an oxygen flare fire and its blowtorch effect on the adjacent hull skin.Such a fire at cruise altitude would be quickly extinguished by hull burn-through and instant oxygen depletion via consequent depressurization outflows. Prior to hull rupture, the pressurization differential would assist the blowtorch weakening on the inside hull skin, speeding up the resulting skin rupture. Once the hull is holed, the oxygen-rich atmosphere is quickly lost and the flare fire quickly gives way to a very cold, dark and windy cavern, sporting just a few residual lights on consoles and panels. All else would be covered by a veneer of soot.
Effects upon pilotsInstinctively averting one’s face from the source of the flash fire might avoid instant incapacitation for the pilot on the opposite side of the cockpit, but once the hull was breached and emergency oxygen was burned away, hypoxia would have been inevitable.It is instructive that when the Apollo capsule experienced a fire in the 100% oxygen atmosphere used at the time, the last astronaut communication from inside the capsule, in which procedures were being ground tested, came 27 seconds after the fire was reported. Not much time. In an airliner, any simultaneous attempt to don an oxygen mask would be in vain, as both pilots’ emergency oxygen supplies are from the source, unprotected by non-return valves. The intense fire would sear the pilots’ lungs.

In May 2014 the Federal Aviation Administration (FAA) issued an airworthiness directive for the B777 aircraft. This AD was one of a number issued in recent years by the FAA covering cockpit vulnerability to fire in a number of different models of transport-category aircraft. This particular AD required the replacement of oxygen hoses in the cockpit. AD 2014-09-06 explained:

“We are adopting a new airworthiness directive (AD) for certain Boeing Company Model 777F series airplanes. This AD was prompted by a report of a fire that originated near the first officer’s seat and caused extensive damage to the flight deck. This AD requires replacing the low-pressure oxygen hoses with non-conductive low-pressure oxygen hoses … We are issuing this AD to prevent electrical current from passing through an internal, anti-collapse spring of the low-pressure oxygen hose, which can cause the low-pressure oxygen hose to melt or burn and lead to an oxygen-fed fire near the flight deck.”

As usual, the FAA seems blind to the larger problem: the lack of fire detection and suppression in the cockpit. Sure, pilots have access to a small hand-held fire extinguisher, but they have no means for inserting the nozzle behind panels, where the fire is most likely to be located. The cockpit, locus of all things electrical, with emergency oxygen lines running in immediate proximity, remains woefully unprotected.

The military has lost aircraft due to fire in the cockpit. At least three cockpit fires in the Navy’s P-3 antisubmarine patrol aircraft resulted in “total loss” of the airplanes on the ground. All three fires occurred in the check valves that were part of the crew’s oxygen system. The military’s sad experience — and corrective actions — have never passed the unseen barrier between the military and civilian communities (see http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080026076.pdf).

There would appear to have never been any imaginative interpretations or prognostications of what might occur when a chafed wiring-initiated oxygen flash-fire should occur in flight. Such a detailed analysis, with effective corrective action, seems long overdue. The FAA Technical Center at Atlantic City, NJ, seems eminently staffed and equipped to undertake such a review.

Alternatively, a university engineering department or separate laboratory could be contracted to perform a fire-vulnerability study of current-generation airliners, to include burn trials of cockpit instruments, knobs, dials, fittings, hoses, lines, display screens, and other equipment, panels and accoutrements found in cockpits. Following component testing, a full-scale cockpit should be subject to fire vulnerability tests to assess the interrelationships of components. Having a university or laboratory conduct such a review would further assure independence.

The findings should lead to wholesale hardening of the cockpit against in-flight fire.

What is needed is a built-in fire detection and suppression system for the cockpit, in which chemical agent is stored in bottles behind panels, with output vents directed to likely sources of conflagration in hidden areas. Until such equipment is installed, the highly-electrified and most-flammable area of the airplane — the cockpit — will remain a flying firetrap.