Narrative:

Captain was flying the aircraft in our descent and we were on a 290 degree heading direct petis NDB at about 7000'. We were a few mi outside petis and we were too high. It was a clear night and the runway was in sight. Ont approach asked if we would like a vector for descent. I accepted and was given a heading of 230 degrees. As I responded with the 230 degree heading the captain disconnected the autoplt and started a turn. I did not set the new heading with the heading selector because I had not been directed to do so, and was making sure the approach check was complete. Normally the autoplt is still in use at this point, but to expedite the descent it had been disconnected just a moment before. As the captain started our right turn, I realized he was turning to a heading different than the one I thought we had been given and I had acknowledged. I told him that I thought the heading approach gave us was 230 degrees, so he asked me to confirm it because he thought the controller said 330 degrees, and he thought I'd read back 330 degrees. As I was querying approach, I noticed the air carrier flight a few mi away, and the TCAS RA 'descend' command went off and we followed its direction. At about the same time this was happening ont approach urgently directed us to turn back to the southwest and continue for 26R. Everything that happened, from the turn to maneuver for descent and the action directed by the TCAS, happened in a matter of seconds. An uneventful landing and taxi-in was accomplished. What caused this? We were kept high, as we always are going into ont, and in our descent the VNAV, for some unknown reason, twice attempted to level us at our previously cleared altitudes. Each time this happened we recognized it right away and corrected for it. Unfortunately, since the normal descent profile keeps us uncomfortably high anyway, this small glitch in our magic made us even higher. Because we were high we were in a position to need to maneuver to lose altitude in a very high density traffic area. The disconnection of the autoplt to help in the descent forced the captain to either update the heading bug on his own, as he elected to do, or ask me to update it for him. He could see I was busy with other things such as radios, checklists and clearing, and it was easier for him to set the bug than ask the task saturated PNF to do it. It didn't register on me right away that the captain had updated the bug to what I thought was the wrong heading until he had already turned to it. The combination of steeply designed descent profiles, congested ATC frequencys, 2-M crews, magic and human limitations al came together to cause this one. TCAS ii helped to resolve it safely.

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Original NASA ASRS Text

Title: ACR CREW TURNS TOWARD WRONG HEADING AND HAS TCAS II RA TO DESCEND.

Narrative: CAPT WAS FLYING THE ACFT IN OUR DSNT AND WE WERE ON A 290 DEG HDG DIRECT PETIS NDB AT ABOUT 7000'. WE WERE A FEW MI OUTSIDE PETIS AND WE WERE TOO HIGH. IT WAS A CLR NIGHT AND THE RWY WAS IN SIGHT. ONT APCH ASKED IF WE WOULD LIKE A VECTOR FOR DSNT. I ACCEPTED AND WAS GIVEN A HDG OF 230 DEGS. AS I RESPONDED WITH THE 230 DEG HDG THE CAPT DISCONNECTED THE AUTOPLT AND STARTED A TURN. I DID NOT SET THE NEW HDG WITH THE HDG SELECTOR BECAUSE I HAD NOT BEEN DIRECTED TO DO SO, AND WAS MAKING SURE THE APCH CHK WAS COMPLETE. NORMALLY THE AUTOPLT IS STILL IN USE AT THIS POINT, BUT TO EXPEDITE THE DSNT IT HAD BEEN DISCONNECTED JUST A MOMENT BEFORE. AS THE CAPT STARTED OUR RIGHT TURN, I REALIZED HE WAS TURNING TO A HDG DIFFERENT THAN THE ONE I THOUGHT WE HAD BEEN GIVEN AND I HAD ACKNOWLEDGED. I TOLD HIM THAT I THOUGHT THE HDG APCH GAVE US WAS 230 DEGS, SO HE ASKED ME TO CONFIRM IT BECAUSE HE THOUGHT THE CTLR SAID 330 DEGS, AND HE THOUGHT I'D READ BACK 330 DEGS. AS I WAS QUERYING APCH, I NOTICED THE ACR FLT A FEW MI AWAY, AND THE TCAS RA 'DSND' COMMAND WENT OFF AND WE FOLLOWED ITS DIRECTION. AT ABOUT THE SAME TIME THIS WAS HAPPENING ONT APCH URGENTLY DIRECTED US TO TURN BACK TO THE SW AND CONTINUE FOR 26R. EVERYTHING THAT HAPPENED, FROM THE TURN TO MANEUVER FOR DSNT AND THE ACTION DIRECTED BY THE TCAS, HAPPENED IN A MATTER OF SECS. AN UNEVENTFUL LNDG AND TAXI-IN WAS ACCOMPLISHED. WHAT CAUSED THIS? WE WERE KEPT HIGH, AS WE ALWAYS ARE GOING INTO ONT, AND IN OUR DSNT THE VNAV, FOR SOME UNKNOWN REASON, TWICE ATTEMPTED TO LEVEL US AT OUR PREVIOUSLY CLRED ALTS. EACH TIME THIS HAPPENED WE RECOGNIZED IT RIGHT AWAY AND CORRECTED FOR IT. UNFORTUNATELY, SINCE THE NORMAL DSNT PROFILE KEEPS US UNCOMFORTABLY HIGH ANYWAY, THIS SMALL GLITCH IN OUR MAGIC MADE US EVEN HIGHER. BECAUSE WE WERE HIGH WE WERE IN A POS TO NEED TO MANEUVER TO LOSE ALT IN A VERY HIGH DENSITY TFC AREA. THE DISCONNECTION OF THE AUTOPLT TO HELP IN THE DSNT FORCED THE CAPT TO EITHER UPDATE THE HDG BUG ON HIS OWN, AS HE ELECTED TO DO, OR ASK ME TO UPDATE IT FOR HIM. HE COULD SEE I WAS BUSY WITH OTHER THINGS SUCH AS RADIOS, CHKLISTS AND CLRING, AND IT WAS EASIER FOR HIM TO SET THE BUG THAN ASK THE TASK SATURATED PNF TO DO IT. IT DIDN'T REGISTER ON ME RIGHT AWAY THAT THE CAPT HAD UPDATED THE BUG TO WHAT I THOUGHT WAS THE WRONG HDG UNTIL HE HAD ALREADY TURNED TO IT. THE COMBINATION OF STEEPLY DESIGNED DSNT PROFILES, CONGESTED ATC FREQS, 2-M CREWS, MAGIC AND HUMAN LIMITATIONS AL CAME TOGETHER TO CAUSE THIS ONE. TCAS II HELPED TO RESOLVE IT SAFELY.

Data retrieved from NASA's ASRS site as of July 2007 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.