Challenger CL604
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 125; Flight Crew Total 9500; Flight Crew Type 320
Situational Awareness
Conflict Airborne Conflict; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors
After finishing our maintenance checks; we were returning to home base. Descending from FL300 to FL250 ATC assigned a left (200 degrees - long way) turn direct to PMD; and asked for 'a tight turn if able'. Having only crew onboard; I elected to disconnect the auto pilot and perform a steep turn. I also reduced power/speed to minimize the radius of the turn. As I approached FL250; I didn't completely arrest the descent; and descended below assigned altitude. Also; while in the turn ATC advised of traffic climbing to FL240 (Gulfstream) perhaps 9 o'clock out of the turn. I saw and reported the traffic; but was later informed that I didn't quite maintain 5 miles (4.7) and 1;000 (700) vertical feet.In retrospect; I had no need to perform a steep turn; or disengage the auto pilot in A airspace. Even if I had elected to do so; a more timely response would have been to terminate the steep turn; to make the altitude capture easier.
CL604 First Officer reported an airborne conflict resulted when he overshot the cleared altitude in descent.