I know this is not practical (considering there is normally not much use to use up to 30 degrees of elevator trim), but if you were on a Boeing 777 or 737, or similar, and the elevator trim was set into said position, and stuck there, would it be possible to safely land said aircraft in that condition?
From the Boeing 737 emergency procedures:
After all attempts fail to free the stabilizer...
- Anticipate higher than normal elevator forces during approach and landing.
- The thrust reduction at flare will cause a nose down pitch.
- Note: Elevator control is sufficient to safely land the airplane regardless of stabilizer position.
Note on terminology: Most jet-liners (including the 777 and 737 as the question requests) use a trimmable horizontal stabilizer (THS), in which the pitch trim is achieved by positioning the whole rear wing up/down -- as opposed to using trim tabs.
(airteamimages.com) THS of an Embraer ERJ-190.
The answer is a resounding Yes! You can safely land an aircraft with Elevator Trim jammed either up or down. Maintaining straight and level flight with Elevators alone can be difficult because the aircraft is sensitive to other conditions, airspeed, wind, etc These can be compensated for through the use of Trim. Trim is a much smaller version of an Elevator, often adjusted up or down by a small wheel between the front seats.
Use of trim can give you much more stability by making smaller adjustments so the Pilot doesn't need to fight the Elevators to maintain height.
During takeoff or landing the affects of a jammed trim can be compensated for by applying small amounts of opposite Elevator.