Probable Cause Of San Francisco Ground Fire Was Wiring Near O2 System

The NTSB has issued a safety recommendation for Boeing 767 aircraft based on a fire that badly damaged a cargo aircraft in San Francisco last year. The 14 page document reads, in part:

"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 (SFO), 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. 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 NTSB determined 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."

There is a lengthy list of recommendations for the FAA from the NTSB regarding this incident.  Among them:

• 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 and modifiers 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 Practices—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)

Also, 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.

FMI: http://www.ntsb.gov/recs/letters/2009/A09_43_53.pdf