A Cessna 208B Super Cargomaster, N926FE, and a Cessna 172S Skyhawk SP, N274MM sustained damage during a ground collision at Honolulu-Daniel K Inouye International Airport (HNL) Hawaii. The Cessna 208B sustained minor damage and the Cessna 172 sustained substantial damage. The solo commercial pilot of N926FE, and private pilot and passenger of N274MM were not injured. Day visual meteorological conditions prevailed at the time of the accident. N926FE operated by Corporate Air as flight 8974. The pilot of the Cessna 208B airplane reported that, during taxi to the runway for departure, his airplane was positioned approximately 50 ft behind the Cessna 172 holding for departure. He added that, he set the condition lever at low idle, and the power lever was set all the way aft to idle. He said he then set the parking brake before diverting his attention to inside of the airplane. Shortly after, he was startled by a noise and vibration, looked up, and realized his airplane had taxied into the airplane in front of him. Probable Cause: The pilot of the Cessna’s failure to set the parking brake before diverting his attention inside the airplane, which resulted in his airplane colliding with the airplane ahead of it on the taxiway.