On June 28, 2008, about 2215 Pacific daylight time, an ABX Air Boeing 767-200, N799AX, operating as flight 1611 from San Francisco International Airport, San Francisco, California, experienced a ground fire before engine startup. The captain and the first officer evacuated the airplane through the cockpit windows and were not injured, and the airplane was substantially damaged. The cargo flight was operating under the provisions of 14 Code of Federal Regulations Part 121. At the time of the fire, the airplane was parked near a loading facility, all of the cargo to be transported on the flight had been loaded, and the doors had been shut.
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 (FAA) failure to require the installation of nonconductive oxygen hoses after the safety issue concerning conductive hoses was initially identified by Boeing.
The safety issues discussed in this report involve the conductivity and the aging of oxygen hoses, the FAA's airworthiness directive process, the proximity of oxygen system components to electrical wiring, the electrical grounding of oxygen systems, the potential for passenger reading lights on transport-category airplanes to become an ignition source, additional smoke detector systems for cargo airplanes, and the effectiveness of ABX Air's continuing analysis and surveillance program. Twelve new safety recommendations to the FAA and one to ABX Air are included in the report.
As a result of the investigation of this accident, the National Transportation Safety Board recommends the following:
To the Federal Aviation Administration:
Require operators to replace electrically conductive combustible oxygen hoses with electrically nonconductive hoses so that the internal hose spring cannot be energized. (A-09-43) Prohibit the use of electrically conductive combustible oxygen hoses unless the conductivity of the hose is an intentional and approved parameter in the design. (A-09-44)
Formalize the airworthiness directive process so that, when an aircraft manufacturer or other source identifies an airworthiness issue with an appliance, coordination with the appliance manufacturer occurs to ensure that the possible safety risks to all products using the appliance are evaluated and addressed. (A-09-45)
Require airplane manufacturers, modifiers, and maintenance personnel to provide positive separation between electrical wiring and oxygen system tubing according to, at a minimum, the guidance in Advisory Circular (AC) 43.13-1A, "Acceptable Methods, Techniques, and Practicesâ€”Aircraft Inspection and Repair," and AC 65-15, "Airframe and Powerplant Mechanics Airframe Handbook." (A-09-46)
Require airplane manufacturers and operators to ensure that oxygen system tubing in proximity to electrical wiring is made of, sleeved with, or coated with nonconductive material or that the tubing is otherwise physically isolated from potential electrical sources. (A-09-47)
Develop minimum electrical grounding requirements for oxygen system components and include these requirements as part of the certification process for new airplanes and approved supplemental type certificate modifications to existing airplanes. (A-09-48)
Once electrical grounding requirements for oxygen system components are developed, as requested in Safety Recommendation A-09-48, require airplane operators and modifiers to inspect their airplanes for compliance with these criteria and modify those airplanes not in compliance accordingly. (A-09-49)
Develop inspection criteria or service life limits for flexible oxygen hoses to ensure that they meet current certification and design standards. (A-09-50)
Once inspection criteria or service life limits for flexible oxygen hoses have been developed, as requested in Safety Recommendation A-09-50, require airplane operators to replace those hoses that do not meet the inspection criteria or that exceed the service life limits. (A-09-51)
Require transport-category airplane operators to (1) perform a one-time inspection of all passenger service unit reading lights installed on their airplanes to ensure that they include rubber boots or use other means to isolate the electrical parts of the assembly and (2) include, in maintenance manuals or other maintenance documentation, information about the importance of this electrical protection. (A-09-52)
Require operators of transport-category cargo airplanes to install smoke detectors in the supernumerary or similar compartment of their airplanes. (A-09-53)
To ABX Air:
Modify your continuing analysis and surveillance program so that all identified chronic discrepancies, such as those affecting the oxygen system on the accident airplane, are effectively resolved. (A-09-54)
Previously Issued Recommendation Reiterated in This Report
The National Transportation Safety Board reiterates the following recommendation to the Federal Aviation Administration:
Provide guidance to aircraft rescue and firefighting personnel on the best training methods to obtain and maintain proficiency with the high-reach extendable turret with skin-penetrating nozzle. (A-07-100)