Super King Air 350
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 142; Flight Crew Total 7930; Flight Crew Type 2230
Situational Awareness
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport
Human Factors
Immediately after takeoff I heard a thump and felt yaw. My copilot looked out the window and saw that the right engine cowling had come open. I looked out mine and saw that the left cowling had also come open and departed the aircraft. I maintained configuration with the gear down and made an immediate left pattern to return for landing. We informed tower that we needed to immediately return to the airfield and we were cleared to land on either runway. I was encountering controllability difficulties in the yaw axis so I maintained speed slow enough to control the airplane and to not exacerbate the structural damage.With the accelerated pace of the short pattern coupled with the immediate landing clearance issued by tower and no other traffic in the area; I did not declare an emergency (in retrospect I probably should have).After an uneventful landing I taxied to maintenance and informed tower that they needed to do a FOD check since we had dropped objects on the runway. After shutdown; I discovered that both engine cowlings had departed the aircraft with one lodging itself on the left horizontal stabilizer.
My co-pilot duties prior to flight directly related to the airplane are to prepare the inside with regards to catering; coffee; icing down drinks. On this day; I did not divert from my usual duties requested of me. At some point after the completed exterior walk around which the captain accomplished; captain left both left and right nacelle doors open for line service to fill oil into engine. I was not made privy to the fact that oil was ordered for the plane; nor that the nacelles were even left open.
King Air 350 flight crew reported they took off without fastening both engine cowlings; which; shortly after takeoff; separated from the aircraft.