Reason: To inform MD-80 operators of the possibility of an uncommanded pitch. up maneuver, provide the necessary information so that the flight crew can identify the problem, and recommend crew action should the problem occur.

Douglas has received six reports from operators who have experienced uncommanded pitch up events after the autopilot was initially engaged or after an autopilot controlled climb was initiated. In each case, the scenario was generally the same. The nose pitched-up to a higher than normal attitude, the "STAB OUT OF TRIM" light illuminated and the aural trim warning sounded. In each event, the crew was able to disconnect: the autopilot and return the aircraft to a normal climb. There has been no case in which the out-of-trim condition of the aircraft approached an unsafe or limiting flight control condition.

Douglas analysis has determined that these events resulted from an electrical short in the alternate trim switch caused by water intrusion in the switch contacts, which caused an erroneous nose-up alternate trim signal, It is unlikely that the failure would occur in the nose down direction because of the orientation of the switch.

When the crew recognizes a developing problem of this type, their first action should be to disconnect the autopilot. The aircraft will continue to pitch up, but: can be controlled by using normal control farces and applying primary trim. DAC does not recommend manual control column inputs during any phase of flight with autopilot still engaged, Therefore, if the crew suspects an uncommanded pitch up or a runaway alternate trim, they should avoid manual pitch inputs using the control column until the autopilot is disconnected.

The flight crew may test the alternate Trim System before flights by slightly altering the existing sequence of trim checks in the Before Start Checklist as follows;

1)  Operate both ALT 3; ONG TRIM switches and check for direction of travel. Observe that the alternate trim stops moving when the alternate trim switches are released.

2) While observing the horizontal trim indicator, momentarily operate each ALT LONG TRIM switch individually to NOSE UP and NOSE DN. Observe that the stabilizer does not move, and that the aural warning does not sound when only one switch is moved in either direction.

3) If the stabilizer moves with just one switch activated, there is a malfunction in the alternate trim switch, and maintenance action is required before flight.

This modified Alternate Trim Check has been included in the April 1994 revision to the Flight Crew Operating Manual (FCOM).

Analysis of the shorted switch components indicate that clear water caused the electric short, rather than spilled coffee or other fluids. Flight crews should use caution when handling liquids in the cockpit and a protective cover should be placed over the console whenever maintenance is being performed.