B737 Undifferentiated or Other Model
Air Traffic Control Fully Certified
Human-Machine Interface; Confusion; Communication Breakdown
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance
Human Factors; Procedure
A B737 was expecting Visual Approach 12L; weather in the area caused wind shift after they checked on. They were told to expect 30R; but to continue to the 12L downwind fix; SHAAD; previously assigned. This was due to opposite direction departure traffic that needed to pass before the B737 could turn toward the 30R final. I turned my attention to other aircraft; coordinating the runway change and a position relief briefing; and then noticed the B737 had turned toward TOY; flying the STAR transition to 30R instead of continuing to SHAAD. This put them in unnecessary proximity to the opposite direction departure at a similar altitude; although the B737 was passing behind the traffic. It created an unsafe situation and separation was not ensured. This is another case of a controller being burned by autopilot; and not the first time I have experienced it. From talking to the crew; they explained that entering the new runway caused the aircraft to fly the 30R transition instead of continuing on the 12L transition as instructed. Would suggest crews do what it takes to follow ATC instructions; even if it means they delay entering the new runway in their system.
On approach; we were given a last minute runway change due to changing weather. At the time; we were at 15 miles northeast of the airport descending for an approach to Runway 12L passing through 11;000 FT MSL. We were subsequently told to now expect Runway 30R. I was the pilot flying; so I immediately started to slow the aircraft in order to configure for a descent and vectors. As I looked away for a moment in order to reference my approach chart; I realized the aircraft was now in a left turn. Trying to be helpful; the pilot not flying had loaded the new runway into the FMC and executed without a crew crosscheck. Unfortunately; the aircraft then began to fly the transition; which we were not cleared for yet. We quickly began the turn back to our original course; but ATC was already inquiring about our heading. After informing them; we were quickly vectored into a left turn anyway. The approach was then completed without any more mishaps.
T75 Controller described an unsafe event when a STL air carrier initiated a wrong turn conflicting with opposite direction traffic; the controller indicating that a premature autopilot change caused the occurrence.