Update, April 5: Flightblogger has this story about how the 737s subject to the AD were identified. As Jon Ostrower closes his piece, he asks what the design changes were. KIRO TV (Seattle) told us that Boeing told it design changes were made to strengthen that area of the airplane.
The FAA said late April 4 that it will issue an airworthiness directive April 5 requiring immediate inspections of 175 Boeing 737-300/400/500 aircraft, following the Southwest Airlines in-flight decompression April 1. Eighty of the aircraft are in the US. Only those with more than 30,000 cycles are affected.
The FAA press release is here.
Other countries with reciprocity airworthiness agreements with the US–such as Germany, for example–will follow the FAA’s AD. Countries without airworthiness agreements with the US aren’t required to follow the FAA AD, and it’s unclear how many aircraft are involved.
KIRO TV in Seattle reports that “hundreds” of aircraft, but fewer than 500, may be subject to inspections globally.
In another development, The Daily Record near Baltimore reported (with the Associated Press) that Southwest is pointing a finger at Boeing for the problem. Whether the tone and intent by Southwest is as severe as The Record suggests is up for debate.
By end of business on April 4, most of the 79 jets Southwest grounded for inspection had been passed and were back in service. Three jets were found to have cracks and inspections continued on the remaining aircraft.