More to the point, how many 747s were grounded until they could fix the center fuel tank problem?
How many MD-11s were grounded after the Swissair crash in 1998? How many Airbus 300s were grounded after American Airlines Flight 587 in 2001? Or 767s after Lauda Air Flight 004 in 1991? Or Airbus 340s after the Air France Flight 447 in 2009?