20111206029249I

Aircraft was on VFR flight from show low, AZ. To falcon field in mesa, AZ. At approximately 10,500 ft MSL. The engine was running normally indicating 25" manifold pressure (mp) at 2500 RPM. The pilot started his let down towards falcon field to the west of roosevelt lake just as he began to pass over four peaks mountain. He started his descent by trimming the aircraft nose down, he then pulled the throttle back to slow his rate of descent. At the time of power adjustment the engine lost power. The pilot states the engine reduced power and the engine manifold pressure was indicating only 15 in. Mp, which was below what was usual for the aircraft during descent. The pilot stated he switched the fuel selector from right to left tank; adjusted the throttle & mixture; engaged the electric fuel pump on "high"; and attempted to restart the engine. When the engine did not restart and he noted further power loss he called falcon field and declared an emergency. He stated his position and said he was not going to make it to falcon field and intended to land at grapevine airstrip (located on the southeast side of roosevelt lake). Falcon tower told him to squawk 7700 and continued to communicate with him until he went below the top of the mountain located between the lake and falcon field. As he descended below the mountain top he realized he would not make it FAR enough east to land at grapevine. He made the decision to land on the highway to the south of the lake. As the aircraft descended towards the east he decided not to deploy his flaps or gear until he was committed to landing based on the aircraft glide. During the glide he attempted to restart the engine again but there was no change in engine output. He set the aircraft to land in a left hand pattern on westbound AZ highway 188. He made a left turn to base leg, and then another left turn to final above the top of a hill on a straight stretch of highway. He checked for traffic on the highway which had no oncoming traffic and one truck going in the same direction but was moving slower that the aircraft glide. The pilot extended the landing gear using the emergency hand pump extension system and extended full flaps. He passed over the top of the truck and landed without incident. He applied brakes to stop the aircraft and pulled off the road to the right. As the aircraft slowed the propeller quit turning. The truck he had flown over drove under his left wing and continued on westbound. The aircraft sustained no damage to the airframe and was pushed to a side road and secured with no further incident. The following day the aircraft was disassembled and moved by trailer to show low airport where the aircraft is normally hangered. Subsequent to the aircraft being reassembled the owner and his mechanic attempted to run the engine on dec. 23. The engine started with great difficulty and would not continue to run except when the electric fuel pump was operating on "high" setting. Even then the engine was running roughly. At that time the engine troubleshooting attempt was suspended because of severe cold weather. As of jan 5, 2012 there has been no further information from the owner or his mechanic regarding mechanical findings which may have been made on the engine. This inspector is awaiting further information on engine troubleshooting findings.