B737-800
Aircraft Equipment Problem Critical
Flight Crew Diverted; Flight Crew Landed in Emergency Condition; General Declared Emergency
Aircraft
At cruise altitude of FL370 Mach .76 in smooth air. Captain attempted to write on his fuel log which was attached to the yoke clip and the yoke moved forward with no resistance. We then found out we could move the yoke forward and aft 6 or 7 inches in each direction without it disengaging the autopilot or changing our flight path.  We were also able to turn the yoke left and right 3 units of travel in either direction without disconnecting the autopilot or changing the flight path of the aircraft. The yoke just moved freely in pitch and roll with no resistance.  We were flying over high terrain in Utah and Colorado. After talking with Dispatch; Maintenance Control; fleet captains; and Boeing Maintenance representatives; we determine the best thing to do was leave the autopilot engaged and autoland the aircraft. We looked at possible landing airports along our route and determined our best option. We declared an emergency and requested vectors and set up for ILS and executed an autoland. After the successful autoland and communicating with ARFF; the Captain taxied the aircraft to the gate.
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B737-800 flight crew discovers during cruise at FL370 that the Captain's yoke can be moved several inches in both pitch and roll without disconnecting the autopilot and without affecting the flight path of the aircraft. After discussions the crew elects to autoland on a long runway; and does so without difficulty.