Skyhawk 172/Cutlass 172
Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Commercial
Flight Crew Last 90 Days 15; Flight Crew Total 1200; Flight Crew Type 1000
Other / Unknown
Conflict NMAC
Flight Crew Took Evasive Action
Human Factors; Procedure; Airspace Structure
I was a passenger on [this flight]. We departed Runway 13 and turned to a heading of 080 at Tower's direction and continued our climb to 8;500 feet MSL. Tower cleared us to Departure frequency. After switching to that frequency; we delayed contacting departure until we were at about 8;200 feet MSL; due to communications traffic. Departure gave us a traffic notification: (Traffic; a Bonanza at one o'clock (don't remember distance and altitude.) Both the pilot and I looked but did not see traffic. Departure gave a second notification: (Traffic; a Bonanza at one o'clock and (I believe) one mile; descending through 8;400 feet.) I looked; did not see traffic; and then noted that our altitude was climbing through 8;400 feet. I leaned forward and saw the Bonanza; previously hidden by the window post.  We pitched up and allowed the Bonanza to pass in front of us at an estimated distance of 50 yards. I believe the pilot of the airplane I was in could not see the traffic due to the cowling obscuring his view of 'one o'clock' while in climb attitude. As the Bonanza was passing in front of us; Departure gave us a traffic alert and advised us to turn right.
C172 pilot flying as a passenger experiences a NMAC with a BE35 at 8;400 feet departing COS. ATC had called the traffic but did not issue instructions until after evasive action had been taken. With the C172 climbing and the BE35 descending; neither saw the other until the last possible moment.