MBB-BK 117 All Series
Flight Crew Air Transport Pilot (ATP)
Situational Awareness
Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
Aircraft Aircraft Damaged; General Maintenance Action
Human Factors
Arrived at work duty ready; aircraft came back from a late flight approximately 30 mins post turnover. Aircraft hangared and pre-flight inspections were completed. No mechanics were at base due to weekend day shift.  I must not have secured the pilot's hydraulics access cowling after pre-flight inspection. Washed aircraft tail but not the front of aircraft as it was clean. Received no flights until end of shift. Pushed aircraft out and checked to see if risk assessment had been accepted and had not. Performed walk around without seeing cowling not fully latched. Waited for a few seconds after walk around and checked that my risk assessment had been accepted. Shut all electronic devices down after calling flight communication about accepted risk assessment. Nurse and paramedic entered rotor arc post start and also performed walk around. Flew to scene location; landed and went to idle. Stayed in aircraft while running at scene. Paramedic performed walk around prior to launch. Flew to receiving hospital. Shortly after touchdown heard a short burst (2-3 second noise from overhead). Paramedic reported parts on the hospital pad. Performed emergency shutdown. Upon post flight saw that pilot's side hydraulic cowling had opened and contacted underside of main rotor blades. All pieces of cowling were accounted for on the hospital pad. No injuries or other damage occurred due to cowling. Flight communications office and maintenance staff call along with write up in log book. Physical hand on the panel during walk around to ensure visual inspection of cowling restraining latches. High visibility paint under latches; or on pins that would be visible (stand out) when latches not fully secured.
MBB-BK117 pilot reported departing with the hydraulic access cowling unsecured; which upon landing contacted the main rotor blades.