Because inconsistencies had been found with the FQIS in other 767s, Boeing had issued a service bulletin for the routine checking of this system. An engineer in Edmonton duly did so when the aircraft arrived from Toronto following a trouble-free flight the day before the incident. While conducting this check, the FQIS failed and the cockpit fuel gauges went blank. The engineer had encountered the same problem earlier in the month when this same aircraft had arrived from Toronto with an FQIS fault. He found then that disabling the second channel by pulling the circuit breaker in the cockpit restored the fuel gauges to working order albeit with only the single FQIS channel operative. In the absence of any spares he simply repeated this temporary fix by pulling and tagging the circuit breaker.