Little is known about the cargo jet fire at this point, but according to the National Transportation Safety Board (NTSB) this much can be stated or inferred with confidence

• The fire occurred 29 June 2008 aboard a B767 freighter operated by Airborne Express (ABX) at about 10:00 o’clock at night.

• The airplane was parked on the ground at San Francisco International Airport, loaded with cargo, and the two-man crew was preparing to start the engines.

• The crew reported smoke and fire just to the rear of the cockpit. It was sufficiently intense to force them to evacuate via a cockpit window. This expedient exit suggests that the crew was unable to use the boarding door on the left side, just aft of the cockpit bulkhead.

• Airport rescue and fire fighting (ARFF) crews extinguished the fire.

• It was reported that a week before the accident, the cargo carrier had received a threat against an unspecified aircraft. However, preliminary examinations have not revealed any indication of an explosive or incendiary device.

• The fire was sufficiently intense to burn holes through the crown of the fuselage, causing what the NTSB described as “substantial damage” to the aircraft.

• The NTSB has sent a team of specialists to begin the investigation.

The cargo loaded aboard is not implicated in the fire. It appears, therefore, that electrical arcing in the wiring started the blaze, and it ignited flammable materials that contributed to the intensity and spread of the fire and resultant fuselage burn-through.

Electrical arcing occurred in the process of powering up the aircraft pursuant to engine start. Since the cockpit voice and flight data recorders are generally activated immediately prior to engine start, it is hoped that useful data from the recorders will be obtained. Irrespective of information on the CVR/FDR, the two pilots escaped unscathed, and interviews with them will doubtless fill in many blanks.

The Airborne Express pilots are luckier than the Swissair flight 111 pilots and passengers on the night of 2 September 1998. All 229 aboard the MD-11 were killed when a fire in the attic space above the forward galley, ignited by arcing, sustained by flammable metalized mylar insulation blankets, and reinforced by a burned-off end cap to an emergency oxygen line, burned its way into the cockpit. Captain Urs Zimmerman was driven out of his seat by molten globs of ceiling plastic falling on him, and First Officer Stefan Loew was unable to maintain control of the airplane in the night sky as the flight instrument screens blanked out as a result of the progressive electrical failures triggered by the fire. The airplane, bound for an emergency landing at Halifax, Canada, crashed into the water at Peggys Cove about four minutes after the crew declared “Mayday” and some 20 minutes after the first wisp of smoke was detected in the cockpit.

As a result of the crash, metalized mylar insulation blankets were removed from hundreds of Douglas-built jets. However, sources at the time said that other types of insulation display similar flammability characteristics, just not to the extent of metalized mylar.

The insulating material on the B767 will be of paramount interest. The Transportation Safety Board (TSB) of Canada said, in the wake of the Swissair flight 111 tragedy, that if all flammable materials used in modern jets were removed, the danger posed by fire would be virtually eliminated. As expressed in its final report of the Swissair accident:

“The TSB believes that the use of a material, regardless of its location, type, or quantity that sustains or propagates fire when subjected to realistic ignition scenarios, constitutes an unacceptable risk [emphasis added], and that, as a minimum, material used in the manufacture of any aeronautical product should not propagate or sustain a fire in any realistic operating environment.”

The Federal Aviation Administration (FAA) is advertising its new radiant panel test, developed in the aftermath of the Flight 111 tragedy, as a means of subjecting thermal acoustic insulation blankets to a more rigorous test of fire resistance. But the TSB found much to say about that test, mainly that the new standard for materials could be more challenging:

• The test sample is oriented horizontally, not vertically. An upright position would be a more demanding test.

• The test sample is not pre-heated. Even though the radiant panel test was derived from an American Society for Testing and Materials (ASTM) protocol, it does not include that procedure’s pre-heat condition.

• The radiant panel test does not indicate how the flammability characteristics of tape, scrim, attachment fittings and so forth would be assessed in various combinations when only three specimens of the insulation must be tested.

• The radiant panel test uses a flame. TSB investigators found that insulation blanket material was far more likely to be ignited by the higher heat of an electrical fire.

In other words, the radiant panel test for qualifying insulation blankets has glaring deficiencies. It should be noted that the ABX B767 first flew in 1986, two years before the Swissair MD-11 crash and therefore before any new fire resistance tests were developed.

FAA actions to improve circuit breaker (CB) protection against arcing also were criticized by the TSB. The FAA is placing great faith in arc-fault circuit breaker (AFCB) technology as a means of preventing dangerous arcing events from frayed, chafed or damaged wiring. AFCB’s are seen as the eventual replacement for thermally-activated circuit breakers. However, circuit breakers work “upstream” of a wire fault, acting after the wire insulation has been breached to prevent further damage. Moreover, the TSB noted that the vaunted AFCB technology the FAA is pursuing (and has only deployed for test purposes in a limited number of aircraft and on non-critical circuits) might not limit the energy of even a fleeting arc to an intensity below the ignition temperature of adjacent materials.

It should also be noted that the attic spaces above the cabin and cockpit are not protected by smoke/fire alarms nor by any active fire suppression systems, as are cargo holds.

As the TSB final report of 2003 on the Swissair in-flight fire tragedy reported, “The board has yet to see significant industry-wide improvements … and is concerned that regulatory authorities and the aviation industry have not moved decisively to ensure that aircraft crews have adequate means to mitigate the risks posed by in-flight fire.” The crews are naked in the face of fire on the ground, too. The NTSB has this near-Swissair event with the ABX jet to recount all that has not been done since the earlier tragedy, and to call for a renewed effort to ensure better fire protection. Bailing out the cockpit window and shimmying down a rope is not an option at altitude.