Basil,
The trim on the 73 (and I think all boeings) works by adjusting the angle of attack of the whole horizontal stabilizer. Trimming nose down with a stuck elevator will lower the nose. In fact in some circumstances, because of the large power-pitch couple the elevator is not powerful enough to lower the nose and as a result the stall recovery drill includes using nose down pitch trim if nose down elevator does not have the desired effect:
• Initiate the recovery:
• Hold the control column
firmly.
• Disconnect autopilot and
autothrottle.
• Smoothly apply nose down
elevator to reduce the angle of
attack until buffet or stick
shaker stops. Nose down
stabilizer trim may be
needed.
This is also the case for a nose high upset recovery:
• Disconnect autopilot and autothrottle
• Apply as much as full nose-down
elevator
• * Apply appropriate nose down
stabilizer trim
• Reduce thrust
• * Roll (adjust bank angle) to obtain a
nose down pitch rate
• Complete the recovery:
- When approaching the horizon, roll to
wings level
- Check airspeed and adjust thrust
- Establish pitch attitude
Exactly the same applies on the 757 and 767
In this incident the crew do not appear to have attempted either of these drills.