The Federal Aviation Administration has ordered airlines within its jurisdiction to perform emergency inspections of approximately 600 Boeing 737 aircraft. There are specific concerns regarding loose elevator tabs on 600, 700, 800, and 900 series aircraft of the 737 model.

The FAA's Emergency Airworthiness Directive was issued following recommendations from Boeing after a Ryanair 737-800 traveling from the Netherlands to Spain experienced "severe vibration" in flight. The flight landed safely, but an inspection found extensive damage to the left elevator, which is the movable flap on the horizontal tail that controls the pitch of the airplane. Fractured mounting lugs are suspected to be the root cause.

"Severe vibration in this attach point is suspected of allowing rapid wear of the joint and resulted in failure of the attach lugs," states the FAA's preliminary incident report. "This condition, if not corrected, could result in a loss of aircraft control and structural integrity."

The 600 through 900 series was the result of the 737 Next Generation redesign at the end of the 1990's, updating the original design going back to 1964. A previous FAA directive that was issued in 2003 resulted in an elevator redesign, but this has not been linked to the current issues.

The FAA is focusing its attention on aircraft that were assembled around the same time as the Ryanair 737. Those aircraft must be inspected within 12 days, while the rest of the 600 which are less likely to be affected must be inspected within 30 days.

Over 3,168 aircraft of the affected models have been delivered.