The Martin 4-0-4 had been chartered to fly tourists to the Grand Canyon. Flight 2504 took off at 09:35 and landed at the National Park Airport around 10:45. Takeoff for the return flight was started a t 14:50 from runway 3. The copilot was to make the takeoff from the right seat. The weather was clear, visibility unlimited, and winds were from 040deg at 15 knots. Immediately after raising the gear a loss of power from the left engine was sensed. The captain took control of the aircraft from the copilot and noticed that the left engine autofeather light was illuminated and the feather button depressed. After passing the runway the aircraft encountered a downdraft and turbulence which overcame the single engine climb performance of the aircraft. The airspeed had decreased to 105 knots and the temperature of the right engine cylinder head was rising rapidly toward the maximum limit, so the captain reduced the manifold pressure about 2 inHg to avoid engine failure. However, the inability of the aircraft to climb and the proximity of the terrain required the crew to return the right engine to full power and select a forced-landing area. The Martin collided with trees 7531 feet past the end of runway 03 and 2447 feet left of the extended centerline. The aircraft was destroyed by post-impact fire. PROBABLE CAUSE: “The unwanted autofeather of the left propeller just after take-off and an encounter with turbulence and downdrafts, a combination which exceeded the aircraft’s single-engine climb capability which had been degraded by the high density altitude and a turn to avoid an obstacle in the flight path. Also, the available climb margin was reduced by the rising terrain along the flight path. The cause(s) for the unwanted autofeather of the left propeller could not be determined.”