B747-400
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 150; Flight Crew Total 9000; Flight Crew Type 4000
Aircraft Equipment Problem Critical
Flight Crew Landed in Emergency Condition; General Declared Emergency
Aircraft
We were given clearance to descend from FL390 to FL380 and after reaching FL387 we were told to immediately climb back to FL390; nothing more was said from Center. About 10 minutes later in our descent passing FL280 for 12;000 we received a 'stab trim unscheduled' EICAS for about 5 seconds followed by a 'Stab Trim 2 and 3' message. The Captain was hand flying at 280 KTS and he immediately sensed the nose wanted to drop. Extra back pressure was required on the control column to keep the nose up. We ran the flight manual procedure for 'Stab trim 2 and 3 inoperative' and that referred us to the jammed stabilizer landing procedure. We contacted Dispatch and Maintenance and coordinated a plan for arrival. We did declare an emergency with Center and got vectors and priority handling for a long straight in ILS. The approach and landing were uneventful but extra back pressure on the column was required during slowing and configuration changes. The stab trim was jammed at 2.8 degrees.
Maintenance informed us that the aircraft had experienced the same problem a couple of weeks earlier. The aircraft was very nose heavy during maneuvers to land.
B747-400 flight crew reported jammed stabilizer on descent. The crew ran the procedure; declared an emergency; and a normal landing ensued. Maintenance advised the same aircraft had a similar issue a few weeks prior.