American Airlines is flying once again after a massive computer glitch grounded all flights nationwide for about four hours this afternoon, reports the Wall Street Journal. The airline had to cancel or delay more than 1,300 flights starting about 1pm Eastern because it couldn't access its reservations system, which controls pretty much every aspect of its flight operations. Despite the all-clear to fly again, American passengers can expect delays and logjams through the night and probably into tomorrow. The airline is offering updates and apologies via Twitter. No word yet on what caused the tech trouble.