The second prototype and test aircraft. Delivered in March 1988 to the Canadian Armed Forces as CC-144 144612, and preserved at CFB Winnipeg after withdrawal from service on 8 April 1993.

This is the second prototype CL-600 and first flew as C-GCGS. It was used by Canadair as a development and trials aircraft. Purchased by CAF and initially unofficially marked as 144600. Designated as a CX-144A and operated by the Aerospace Engineering and Test Establishment at CFB Cold Lake, Alberta. Now on display in this public area adjacent to CFB Winnipeg.

C-GCGS-X shares the ramp with C-GXKQ-X during flight testing of the Challenger.

This is the second prototype Challenger, used by Canadair for development and certification trials. Sold to the Canadian Air Force February 28, 1988 for development of the CE-144 and CP-144 programs. It was assigned to the Aerospace Engineering and Test Establishment at CFB Cold Lake, Alberta. Withdrawn April 8, 1993, the aircraft is now displayed outside Air Force Headquarters, CFB Winnipeg, MB.