Ce-560 flight crew reported that declining a ferry flight due to fatigue.

Attributes
ACN	1517679
Time
Date	201802
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Make Model Name	Citation Excel (C560XL)
Operating Under FAR Part	Part 91
Flight Phase	Parked
Flight Plan	IFR
Person 1
Function	Pilot Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Person 2
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Deviation - Procedural Other / Unknown

Narrative:

During a very long duty day (and week) on a flight that blocked 4.5 hours we became aware of how fatigued we were. We completed the flight safely but when we landed the company asked us if we'd be willing to ferry the plane from to ZZZ. Ferrying that plane would have been dangerous due to our fatigue level. So I called in fatigued. Without doing that ferry flight...I worked [60+] hours in 7 days. Supposedly [the company] has a fatigue software that they are running. If it showed we were able to do that ferry flight without being fatigued then I suggest they scrap or tweak the fatigue software program because we were both exhausted.if a part 121 pilot can't work 7 days in a row without a 24 hour break; why can we? The regulations need to change!

Original NASA ASRS Text

Title: CE-560 flight crew reported that declining a ferry flight due to fatigue.

Narrative: During a very long duty day (and week) on a flight that blocked 4.5 hours we became aware of how fatigued we were. We completed the flight safely but when we landed the company asked us if we'd be willing to ferry the plane from to ZZZ. Ferrying that plane would have been dangerous due to our fatigue level. So I called in fatigued. Without doing that ferry flight...I worked [60+] hours in 7 days. Supposedly [the Company] has a fatigue software that they are running. If it showed we were able to do that ferry flight without being fatigued then I suggest they scrap or tweak the fatigue software program because we were both exhausted.If a Part 121 pilot can't work 7 days in a row without a 24 hour break; why can we? The regulations need to change!

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.