Rf Coupling into the Fuel Tank of a Large Transport Aircraft from Intentionally Transmitting Peds in the Passenger Cabin

An investigation was performed to study the potential for radio frequency (RF) power radiated from Portable Electronic Devices (PEDs) to create an arcing/sparking event within the fuel tank of a large transport aircraft. This paper describes the experimental methods used for measuring RF coupling to the fuel tank and Fuel Quantity Indication System (FQIS) wiring from PED sources located in the passenger cabin. To allow comparison of voltage/current data obtained in a laboratory chamber FQIS installation to an actual aircraft FQIS installation, aircraft fuel tank RF reverberation characteristics were also measured. Results from the measurements, along with a survey of threats from typical intentional transmitting PEDs are presented. The resulting worst-case power coupled onto fuel tank FQIS wiring is derived. The same approach can be applied to measure RF coupling into various other aircraft systems. Introduction Separate papers [1,2] describe the approach and the results from an investigation into RF threats to the Fuel Quantity Indication System (FQIS) wiring. This work was in support of the investigation of the TWA-800 accident in 1996 at the request of the National Transportation Safety Board. The goal was to determine whether there was enough RF energy/power on the FQIS wiring to create a sparking/arcing event inside the aircraft’s Center Wing Tank (CWT). A sparking/ arcing event in the CWT may increase the probability of creating an explosion in the tank, leading to a catastrophic accident. RF threats include sources external and internal to an aircraft. External RF threats, as provided by the Joint Spectrum Center [3], include the worst case RF environment at the aircraft at the time of the accident. They were calculated based on known data about the transmitters and the distance to the aircraft. RF sources internal to the aircraft include portable electronics devices (PEDs), which consist of intentionally transmitting devices such as portable phones and two-way radios, and unintentionally transmitting devices such as laptop computers and game devices. In terms of total radiated power, intentionally transmitting PEDs are much more likely to be a threat as many of them may radiate up to 6 watts of RF power. Unintentionally transmitting devices radiate at levels below intentional radiators, even when damaged, and are not considered as a threat in this case. This paper focuses on the measurement of the potential threats to the CWT and its wiring due to intentionally transmitting PEDs in the passenger cabin. The approach includes identifying PED threats and performing measurements on a retired Boeing 747 airplane of the RF coupling to the CWT and its wiring. Together, the PED threats and the worst case coupling factors provide an upper bound on the maximum threats to the fuel tank and it’s wiring. This result is then compared with the power requirement for creating a spark/arc, as determined through laboratory testing, to determine if there