A B737-300 Captain reported that while at cruise on a maintenance ferry flight for an elevator anomaly a great deal of aileron input was required to counter a roll motion. An emergency was declared and the flight continued to its nearby destination.

Narrative

While performing a maintenance ferry one of the Mechanics on board was asking us to comment on if we felt anything out of the ordinary. The ferry was because there was a 3/8 in. amount of play in an elevator bushing. En route we noticed the airplane was not turning toward the next FMC fix. Since I was talking to the Mechanic at the time the First Officer turned off the auto pilot and auto throttle and hand flew the airplane. He needed to hold the yoke at about 45 degrees to remain level. When this happened the Mechanic said land the airplane ASAP. I declared an emergency and we decided the best course of action and nearest suitable airport unless the condition worsened would be our destination. After seeing none of the suggested QRH items applied we tried to see if using the aileron trim would fix the problem. At first it appeared to not fix the problem and the Mechanic checked the circuit breaker. I tried the trim again and held it for a longer time period and it corrected the problem but required 2-3 units right at 230kts and approx 1- 1 1/2 units when we slowed to 210 knots. We continued to our scheduled destination and after landing went straight to the hanger. The event occurred because the two pilots assigned this flight were not check airman or Maintenance Pilots. We were apprehensive about taking an airplane where we were told that even Mechanics could be on. Once the Mechanics told us they would ride on this airplane if Maintenance Control allowed it. I called Maintenance Control and they approved adding the Mechanics to the ferry permit. The Mechanics told us that they had spent almost 2 days with engineering and Maintenance Control getting the airplane approved for the ferry flight. They made it sound like it was not easy getting approval. So when this out of the ordinary event happened and the Mechanic said 'land the airplane ASAP' we thought it was a serious problem. The immediate QRH actions were performed; the emergency declared to get us priority handling and then the non-immediate actions were done mitigating the need for the emergency. Do not assign regular crew members to ferry a plane that requires a permit to ferry before Flight Ops determines if that flight should be flow by a regular line pilots instead of Maintenance Pilots.