While the aircraft was being prepared for its return to Edmonton, a maintenance worker decided to investigate the problem with the faulty FQIS. To test the system he re-enabled the second channel, at which point the fuel gauges in the cockpit went blank. Before he could disable the second channel again, however, he was called away to perform a floatstick measurement of fuel remaining in the tanks, leaving the circuit breaker tagged (which masked the fact that it was no longer pulled). The FQIS was now completely unserviceable and the fuel gauges were blank.