Flight Crew Air Transport Pilot (ATP)
Fatigue
Deviation / Discrepancy - Procedural FAR; Deviation / Discrepancy - Procedural Published Material / Policy
General Flight Cancelled / Delayed; General Work Refused
Procedure
I am writing over the fatigue inducing schedule I had and for the fatigue call I made.The previous day; we had an [early] show for [standby]. This was the 2nd day of before [a later] show [from a different time zone]; so it wasn't too early but was still before my normal time I plan for work. Then at the end of [standby show]; we were shut down and given a XA00 local show for [standby] until XG45 [on day 3]. Due to the early show and no planning my previous nights sleep to adjust to this; I was unable to get to bed until XS00 and sleep 5 hours waking up at XX00 [day 4]. As the [standby] was only until XG45; I was comfortable I could make it this long on 5 hours sleep. However; at XG30; my brief changed with a XI00 ferry to ZZZ which would have been a 2+48 flight landing at XJ48. This would have been a 10+48 duty day. There was no way I could complete this; so I fatigued. I can't believe the Fatigue Mitigation Software would even allow for this. This wouldn't have even been legal under part 117 that regulates 121 passenger flights. As this duty uses the most modern science; I tend to use this as a guide for fatiguing as it closely represents how I fatigued I have been in the past when I would exceed the duty times for part 117. For part 117; if I was acclimated to my home time; a XA00 show would be XX00 and good for 9 hours. Even if I acclimated to [local] time; a XA00 show is good for 10 hours. Therefore; this 10+48 wouldn't even work for this. The Fatigue Mitigation Software at a minimum needs to reflect the part 117 duty times as these have been done taking into account modern science in determining fatigue.
Corporate Jet Captain reported 'fatigued' when assigned flight at the end of 8 hour aircraft standby duty.