On August 25, 1999, about 0620 Alaska daylight time, a float equipped DeHavilland DHC-2 airplane, N930TG, sustained substantial damage during takeoff from a remote lake, about 2 miles east of Iliamna, Alaska, at position 59 degrees 45 minutes north latitude, 154 degrees 22 minutes west longitude. The airplane was being operated as a visual flight rules (VFR) flight under Title 14, CFR Part 135, when the accident occurred. The pilot/owner was operating the airplane for his fishing guide business, Iliaska Lodge, Inc., of Iliamna. The certificated commercial pilot, and four passengers aboard, were not injured. Visual meteorological conditions prevailed, and company flight following procedures were in effect. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge on August 25, the pilot related that prior to his takeoff attempt, he noted that the lake surface had 2 feet tall, rolling swells. He said that during the takeoff run, before a safe flying airspeed was attained, the airplane floats struck a large wave, and the airplane lifted off the water prematurely. He said that before he could react, the left wing stalled, and the airplane collided with the water. During the collision, the floats were torn off the airplane, and the airplane sank. The airplane sustained substantial damage to the fuselage, empennage, and wings. In the Pilot/Operator report (NTSB form 6120.1/2) filed by the pilot, he wrote: "...I think the left flap and aileron partially retracted while the airplane was still on the step, prior to takeoff. Perhaps striking the larger swell caused the flap to retract." A Federal Aviation Administration (FAA) operations inspector, Anchorage Flight Standards District Office, traveled to the accident scene, and was present while the airplane was being recovered from the water. The inspector reported that no preaccident mechanical anomalies were noted with the airplane's flap or aileron systems. He added that the following day, prior to daylight conditions (dawn), he observed other operators departing with low light conditions which made it difficult to see the rolling swells. The closest official weather observation station is Iliamna. On August 25, 1999, at 0553, an Aviation Routine Weather Report (METAR) was reporting in part: Wind, 259 degrees (magnetic) at 7 knots; visibility, 10 statute miles; clouds, 7,500 feet broken; temperature, 51 degrees F; dew point, 46 degrees F; altimeter, 29.52 inHg. Official civil twilight for Iliamna was at 0610.