identified as the ignition source for the surge tank fire that destroyed a 747 near Madrid in 1976. This was not considered proof of a source of ignition. Evidence of arcing was found in a wire bundle that included FQIS wiring connecting to the center wing tank. Arcing signs were also seen on two wires sharing a cable raceway with FQIS wiring at station 955. The captain's CVR channel showed two "dropouts" of background power harmonics in the second before the recording ended (with the separation of the nose). This might well be the signature of an arc on cockpit wiring adjacent to the FQIS wiring. The captain commented on the "crazy" readings of the number 4 engine fuel flow gauge about 2 1/2 minutes before the CVR recording ended. Finally, the CWT fuel quantity gauge was recovered and indicated 640 pounds instead of the 300 pounds that had been loaded into that tank. Experiments showed that applying power to a wire leading to the fuel quantity gauge can cause the digital display to change by several hundred pounds before the circuit breaker trips. Thus, the gauge anomaly could have been caused by a short to the FQIS wiring. The NTSB concluded that the most likely source of sufficient voltage to cause ignition was a short from damaged wiring, or within electrical components of the FQIS. As not all components and wiring were recovered, pinpointing the source of the necessary voltage was not possible. Report conclusions The NTSB investigation ended with the adoption of the board's final report on August 23, 2000. The board determined that the probable cause of the TWA 800 accident was: In addition to the probable cause, the NTSB found the following contributing factors to the accident: During the course of its investigation, and in its final report, the NTSB issued 15 safety recommendations, mostly covering fuel tank and wiring-related issues. Among the recommendations was that significant consideration should be given to the development of modifications such as nitrogen-inerting systems for new airplane designs, and where feasible, for existing airplanes. Controversy The NTSB's conclusions about the cause of the TWA 800 disaster took four years and one month to be published. The FBI's earliest investigations and interviews, later used by the NTSB, were performed under the assumption of a missile attack, a fact noted in the NTSB's final report. Six months into the investigation, the NTSB's