Missing an Important Factor
It seems to me that the editor’s note, "Consequence of a Tragedy" (September 2002, page 6), misses the most important factor in the European midair collision between a DHL 757 and Bashkirian Airlines Tu-154. It would appear that the root cause was a systems engineering failure–that when analyzing the impact of the traffic alert collision avoidance system (TCAS), the possibility (or, as it now seems with hindsight, the inevitability) of conflicting air traffic control and TCAS instructions was not identified. Although all the hardware and software worked as advertised, it could be argued that this was a TCAS-induced collision.
David Craig
Lead Technologist
BAE Systems
Edinburgh, UK
A Safer Solution
I read your Safety in Avionics column in the August issue of Avionics Magazine, titled "Clueless in the Cockpit" (page 45), which analyzed an in-flight fire in the cargo area of an Air Canada B767-300. As you noted, a heater tape wrapped around one of the potable water lines caused the fire. This application of heater tape is common on aircraft today. In fact, Cox & Co. manufactures a similar type of heater tape (called "Ribbon Heater") to the one that caused this fire. Boeing and other airframe manufacturers and finishing centers use our Ribbon Heater on various aircraft.
We met with the Transportation Safety Board two months concerning this incident because, even though a Cox & Co. heater did not cause the fire, our Ribbon Heaters were installed on the Air Canada plane.
Cox & Co. also manufactures a product called an "Innerline Heater," used in the aviation industry for potable water supply and drain lines. It is much safer to use on water lines than the older-style tape heaters, because an Innerline Heater is installed (actually, inserted) into the water line, as opposed to wrapped on the outside of the water line. Tape heaters used on the outside of water lines have shortcomings, such as watt density being subject to an installer’s technique and heaters being damaged externally. The heater also can short-circuit to the pipes or structure. Heaters are not ultra-high-temperature products (usually around 250 degrees F), [but] they can overheat adjacent material, which can cause a fire, as well.
With Innerline Heaters, it is virtually impossible to cause an event such as the Air Canada incident, since the heater is contained within the line itself. Cox & Co. invented the Innerline Heater roughly 30 years ago and has since sold more than 25,000 units to Boeing, McDonnell Douglas, Airbus, Gulfstream, Bombardier and Embraer for use on potable water lines.
In nearly 2 billion hours of operation, the Innerline Heater has never caused any incident that even remotely resembles the Air Canada accident. With its high-temperature capability (around 450 degrees F), the Innerline Heaters are extremely safe to operate and have an almost indefinite life.
Ray Bozek
Manager, Customer Support
Cox & Co.
New York, N.Y.