I don't know, but all of these groundings are a little suspect. With fuel at an all-time high and profit margins razor-thin if at all existent, it wouldn't shock me if carriers were intentionally grounding some of their fleet to simply save money rather than to comply to general safety concerns.

I think we're reaching a point that it may be cheaper for carriers like AA to simply cancel flights for a "safety check" than to actually fly them, even if they're 80%+ booked.