All U.S.-operated MD 900-series helicopters were ordered grounded pending inspection of their main rotor retention bolts (P/N 900R3100001-103). An FAA emergency AD (2003-13-51) issued on June 23 was prompted by two cases of bolt failure, both occurring aboard MD 902s operating in the UK. If inspection shows no free travel of the attached main rotor components or visible cracks, the directive requires immediate replacement and a visual check of the bolt before each subsequent engine start. At intervals of no more than six hours, a cam lever force inspection must also be performed.