On February 4, 2003, about 0510 Pacific standard time, a Beech E18S twin-engine airplane, N48K, sustained substantial damage after impacting terrain shortly after takeoff from the Skagit Regional Airport (BVS), Burlington, Washington. The airplane is registered to Comanche Air Inc., Winthrop, Washington, and was being operated by Methow Aviation, of Burlington, Washington. The commercial pilot, sole occupant, was not injured during the 14 CFR Part 91 local flight. Visual meteorological conditions prevailed and no flight plan was filed. During a telephone interview and subsequent written statement, the pilot reported that during his preflight inspection he noticed ice and frost adhering to the airplane. He stated that after applying glycol to the wings and polishing and brushing off the frost, "then they were smooth." The pilot further stated that he let the engines warm up for 15 to 20 minutes before "taking it around the patch once to clear the airplane of the ice, and to make sure everything was working properly." Before releasing the brakes to take off, the pilot brought the power up on both engines "to make sure everything was in the green." After releasing the brakes, the pilot stated "I slowly brought the power up, maintaining 2000 rpm on the propellers." The pilot stated, "I tried to baby the engines using a less than max power for the departure." The tail of the airplane came up about 3/4 of the way down the 5,477 foot runway, and "seeing the end of the runway coming up, I added more power and pulled it off the ground." The pilot also reported that after seeing a "positive rate" he retracted the landing gear, and shortly thereafter "I felt the airplane mushing, like a stall. I then added more power, but the aircraft kept mushing, and then it impacted terrain with power on both engines." The aircraft came to rest in an open field located approximately 1/4 mile from the end of runway 28. After impact, the aircraft's engines separated at the firewall. Subsequently, the aircraft veered 90 degrees to the right, coming to rest in an upright position perpendicular to the runway. There was no post-impact fire. An FAA inspector, who traveled to the accident site, reported that both engines had separated from the firewall, the right wing sustained spar damage, both vertical stabilizers and rudders were bent. At 0505, the weather observation facility located at BVS reported wind calm, visibility 4 statute miles, temperature -1 degree C, dew point -1 degree C, and an altimeter of 30.45 inches of Mercury. The Director of Maintenance (DOM) for Methow Aviation reported that he arrived at the accident site about 0845 and observed ice adhering to most of the airplane. The DOM stated that the company does have a de-icing procedure which is normally done by the pilot.