As aircraft started its descent for approach, the crew noticed that the airplane would not follow autopilot (a/p) commands. The a/p was disconnected and the first officer noted that pitch control forces were higher than expected. The airplane executed a go around and flew to a holding pattern for further diagnosis.

As the airplane departed the hold, the Captain applied higher force to the control column and "with a jerk-type motion the jam was gone". Afterwards, the controls operated normally and the airplane landed without further incident.

Examination of the airplane after the event indicated that water and ice had collected on the elevator control system components in the empennage. The pilot reported that the airplane experienced rain in Cancun but there were very few clouds on the 10-hour flight to Zurich.

Another event with similar characteristics was reported by another operator on approach to Paris, France on March 27, 2001 (see DCA01WA032).

The Federal Office for Civil Aviation of Switzerland and the AAIB-Switzerland investigated this event with the assistance of Boeing and the NTSB.

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