ABX B762 San Francisco fire due to design, wiring flaws

THE US National Transportation Safety Board (NTSB) says the fire aboard an ABX Air Cargo Boeing 767-200 at San Francisco was probably caused by "the lack of positive separation between wiring and electrically conductive oxygen system components."

The NTSB's final report found that the fire in June 2008 started while the crew was preparing for departure just minutes after the crew had performed their oxygen check.

"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," said the NTSB report.

"The first officer went to turn off the lights. 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," said the report.

The Aviation Herald of Salzburg, Austria, said that a pilots aboard the aircraft received minor injuries and the fire forced the evacuation of more than 100 workers from the airport's Air Mail facilities. The heat and smoke were reported to have caused severe damage not only to the fuselage, but also in the cockpit.

The Boeing 767-200 that was scheduled to operate a cargo flight from San Francisco, California to Wilmington, Ohio had been parked at a ramp, with its engines shut down for loading and fuelling when the fire broke out behind the cockpit.

"Contributing to this accident was the Federal Aviation Administration's failure to require the installation of nonconductive oxygen hoses (by issuing an airworthiness directive), after the safety issue concerning conductive hoses was initially identified by Boeing," the report is cited as saying in the Aviation Herald.

The NTSB report went on to say that "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.

"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."

It went on the conclude: "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 programme did not include adequate actions for resolving the discrepancies and preventing additional oxygen leaks from occurring."

An earlier report issued by the Aviation Herald in July 2009 said that NTSB had "issued a safety recommendation to require operators to replace electrically conductive with electrically non-conductive oxygen hoses."

It added that during the course of the investigation into the fire onboard the aircraft the NTSB also found that the reading lights located in the passenger service units could become a potential source of ignition to nearby combustible materials.

As a result, the agency recommended back then that "all reading lights are to be mounted with rubber boots or other means to provide a greater level of electrical protection."

Source: www.schednet.com