CANBERRA, Australia — Qantas Airways grounded its global fleet Saturday, suddenly locking out striking workers after weeks of disruptions an executive said could close down the world's 10th largest airline piece by piece. Australia's government called an emergency arbitration hearing that lasted nearly two hours before the judges adjourned it to issue a decision later Saturday night. At least 60 Qantas flights were in the air and continued to their destinations, and at least one taxiing flight stopped on the runway, a flier said.