HISTORY OF FLIGHT On August 5, 2001, approximately 2015 Pacific daylight time, a Cessna 336 tandem twin engine airplane, N3838U, experienced a loss of power in the aft engine and collided with a guardrail during an off-airport emergency landing on highway 14 near Palmdale, California. The airplane was registered to, and operated by, the private pilot as a personal flight under the provisions of 14 CFR Part 91, and sustained substantial damage. The pilot, the sole occupant, received serious injuries. Night visual meteorological conditions prevailed at the time of the accident, and a flight plan had not been filed. The flight had originated from the El Monte Airport, El Monte, California, and stopped at the General William J. Fox Airfield, Lancaster, California. The flight then departed Lancaster at 2000, with a final destination of El Monte. The National Transportation Safety Board investigator conducted an interview with the pilot. The pilot stated his plan was to fly to eight local area airports to get current. The first leg of the flight was flown earlier that afternoon with no mechanical discrepancies noted. Dusk light conditions existed when the pilot prepared for the flight so he elected to fly to El Monte instead of flying to the remaining airports. The pilot reported that during climb out, about 4,500 feet, both engines started to lose power; however, he did not hear either engine sputter. He indicated that both engines were not producing enough power to maintain flight. The airplane kept descending, so the pilot attempted to land the airplane on the highway, but landed short on the shoulder and collided with the guardrail. In a written statement submitted by the pilot, he stated the airplane climbed with its "usual" power and was leveled off at 4,500 feet. Moments later he noticed the airplane was losing altitude and he therefore, applied full throttle and placed the propeller controls full forward, but nothing helped. The pilot realized he was going down and headed toward the lights of Palmdale. The pilot further stated that the freeway seemed to be the best landing place, but turned out to be "quite twisty." The pilot noted during the descent he "could hear lots of engine." PERSONNEL INFORMATION The private pilot held ratings for single engine, multiengine, and instrument airplanes. The pilot was issued a third-class medical certificate on September 1, 1999, with a limitation to "wear corrective lenses for near and distant vision." The medical certificate also indicated it was not valid after September 30, 2001. According to the pilot, the latter limitation was in place because of a heart issue and he had to go in for a checkup every 6 months. The pilot reported having had accumulated a total of 1,266 flight hours, of which 94 hours were flown in the same make and model as the accident airplane. Tower personnel reported to the Federal Aviation Administration (FAA) Aviation Safety Inspector, who responded to the accident site, that the pilot landed and departed the General William J. Fox Airport without obtaining a clearance. The FAA inspector also spoke with a flight instructor, who had been flying with the accident pilot for the past 6 months. He reported that he recommended that the pilot not fly his airplane alone. WRECKAGE AND IMPACT INFORMATION The airplane came to rest down in a ravine in rough and uneven terrain adjacent to the highway. The California Highway Patrol sergeant, who responded to the accident site, reported that the landing gear had been torn off of the airframe, and the guardrail had been displaced about 15 feet. According to first responders, fuel was found leaking from the airplane. A salvage facility relocated the airplane to a secure location for further examination, and reported draining 80 gallons of fuel from the airplane's fuel system. TESTS AND RESEARCH On August 22, 2001, the Safety Board investigator-in-charge, along with representatives from the engine and airframe manufacturer, examined the airplane and engines at Aircraft Recovery Services, Pearblossom, California. It was noted during the examination, that both engine primers were found unlocked. The rear engine primer was found pulled out approximately 1 inch. The top spark plugs were removed from both the front and aft engines. The front engine spark plugs displayed normal wear and operational coloration according to the Champion Check-A-Plug AV-27 chart. The rear engine's top spark plugs and cylinders appeared very dark and displayed a sooty appearance. The Check-A-Plug chart indicated the plugs had experienced a rich mixture setting. Both magnetos on each engine produced a spark when the engine crankshafts were rotated, and thumb compression and valve operation were verified on each cylinder. In the pilot operating handbook for the airplane, the primer is listed as an optional feature to assist in cold weather operations. The checking of the primer position is not included in the operating handbook's checklists.