The FAA issued an emergency airworthiness directive–2013-10-52–for GE90-110B1 and GE90-115B engines on May 16 after two reports of transfer gearbox assembly (TGB) failures prompted in-flight engine shutdowns. Investigations revealed the cause as TGB radial gear cracking and separation. The AD prohibits the operation of any aircraft with either engine installed five days after receipt of the directive.