Date: 201305
Local time of day: 0001-0600
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: Turbulence; 10
Light: Dusk
Aircraft: Stratolifter (C-135 / 717)
Operator: Air Taxi
Operating under: Part 91
Flight plan: None
Mission: Ferry / Re-Positioning
Flight phase: Cruise
Airspace: Class G ZZZ
ATC / advisory: CTAF ZZZ
Reporter organization: Air Taxi
Reporter function: Single Pilot; Pilot Flying
Reporter qualification: Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Commercial
Human factors: Fatigue
Anomaly: Other Fatigue
Detector: Person Flight Crew
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Procedure; Staffing; Human Factors
Primary problem: Procedure

Narrative: While on the Part 91 leg (repositioning flight); I was the PIC of [Company] EC135. This was the second 'mission' of the evening in which I had flown 6+ hours and did not have a rest period between. At this time [Company] had no line pilots and I was the Chief Pilot. The Director of Operations had advised me that we were on a 24/7 on-call basis approved with our POI. I was instructed that if a call would be taken I had to have 10 hours rest before the next flight or I had to accomplish multiples of flights within 14 hours and then take a 10 hour required rest period under FAR part 135 rules; however a refueling or repositioning leg was to fall under FAR part 91 rules. While on my 'off' time I was required to train new-hire pilots from the hours of XA:00 am to XH:00 pm. On the day prior to the occurrence I was prepping new pilot records in preparation for their arrival. I was asked to do this on my time 'off' and not 'sign in' until a flight was activated. That evening we were activated for one flight that was accomplished and unremarkable; followed by a second flight that was accomplished under FAR part 135 with no issue. We were on the Part 91 leg repositioning the aircraft back to base. This flight had clear VMC weather and no ceiling. The flight originated during the hours of the night and during the Part 91 leg had become daylight. It was during this leg while the autopilot was engaged for a direct GPS route at approximately 800 FT AGL that I found myself fatigued during flight. I typically carry an energy drink in my flight suit; however I had taken it earlier during the first flight of that night. I noticed that I was fatigued and would open the pilot's side window and would vent air onto my face to remain alert.I realize that flying while fatigued is a safety risk. I should have landed the aircraft at the closest airport and taken a rest period before continuing to fly home. I believe that helicopter EMS should only be flown under part 135 rules every leg. I also feel that in order to prevent fatigue in the future no MedEvac operation should be allowed to operate with a single pilot on a 24/7 on-call basis. I also feel Medical crewmembers should be essential in ensuring that a pilot is not fatigued. Asking questions; interacting; becoming a part of the crew versus sleeping themselves in the cockpit.




Synopsis: EMS Helicopter pilot contends that his company's policy of operating under both FAR Part 91 and Part 135 subverts crew rest requirements and leads to crew fatigue.