Narrative:

In a descent to 3500 ft, we were given multiple heading changes. During the heading changes, the controller kept reporting MD80 traffic for the parallel runway, and iterated that we needed to have visual separation so he could clear us for a visual approach. On TCASII, the traffic was approximately 2000 ft below our altitude and 2-3 mi north of our position. Both of us transmitted that we had the traffic in sight, possibly blocking xmissions from the controller. The controller then asked us our altitude. I responded, '...thirty-two hundred ft, correcting.' he then gave us a heading change to 210 degrees, and began to vector us around for a second approach. I believe that my roll in backing up the captain was degraded by the following factors: the requirement for outside visual scan for reported traffic. Multiple traffic calls from ATC focusing my attention to other aircraft. Multiple heading changes. Configuring aircraft for landing while trying to find other traffic. 2 different altimeter system, one driven by an air data computer, the other by raw barometric input. Another more insidious factor is the developed trust in the other crew member. Having flown many legs with the other pilot over the course of the month, I was extremely impressed by his competent adherence to both FAA and company mandated regulations and procedures while maintaining a calm, professional demeanor in the cockpit. Regardless of the above factors and considerations, my opinion is that there is no instrument, device, or gadget can replace an aviator's skill and judgement. This occasion has only reinforced my belief that a pilot's best safety device is his/her own training and self-discipline. Supplemental information from acn 453712: corrective action for me is to definitely increase my situational awareness of the aircraft's position in space compared to that assigned, and to verify clrncs for the lda or visual approach. And altitude capture feature on the autoplt would have precluded any part of this incident from occurring. Possibly simultaneous radio xmissions precluded us from communicating our visual acquisition of the low traffic to approach control, or for him advising us to check our altitude sooner. The altitude alert tone function (notifying pilots within 300 ft approaching a selected altitude, and passing 300 ft past a selected altitude) should be a continuous tone once past the selected altitude to prevent inadvertent altdevs.

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Original NASA ASRS Text

Title: AN MLG FLC DSNDED BELOW THE ASSIGNED ALT ON APCH TO STL.

Narrative: IN A DSCNT TO 3500 FT, WE WERE GIVEN MULTIPLE HEADING CHANGES. DURING THE HEADING CHANGES, THE CTLR KEPT RPTING MD80 TFC FOR THE PARALLEL RWY, AND ITERATED THAT WE NEEDED TO HAVE VISUAL SEPARATION SO HE COULD CLR US FOR A VISUAL APCH. ON TCASII, THE TFC WAS APPROX 2000 FT BELOW OUR ALT AND 2-3 MI N OF OUR POS. BOTH OF US XMITTED THAT WE HAD THE TFC IN SIGHT, POSSIBLY BLOCKING XMISSIONS FROM THE CTLR. THE CTLR THEN ASKED US OUR ALT. I RESPONDED, '...THIRTY-TWO HUNDRED FT, CORRECTING.' HE THEN GAVE US A HEADING CHANGE TO 210 DEGS, AND BEGAN TO VECTOR US AROUND FOR A SECOND APCH. I BELIEVE THAT MY ROLL IN BACKING UP THE CAPT WAS DEGRADED BY THE FOLLOWING FACTORS: THE REQUIREMENT FOR OUTSIDE VISUAL SCAN FOR RPTED TFC. MULTIPLE TFC CALLS FROM ATC FOCUSING MY ATTN TO OTHER ACFT. MULTIPLE HEADING CHANGES. CONFIGURING ACFT FOR LNDG WHILE TRYING TO FIND OTHER TFC. 2 DIFFERENT ALTIMETER SYS, ONE DRIVEN BY AN ADC, THE OTHER BY RAW BAROMETRIC INPUT. ANOTHER MORE INSIDIOUS FACTOR IS THE DEVELOPED TRUST IN THE OTHER CREW MEMBER. HAVING FLOWN MANY LEGS WITH THE OTHER PLT OVER THE COURSE OF THE MONTH, I WAS EXTREMELY IMPRESSED BY HIS COMPETENT ADHERENCE TO BOTH FAA AND COMPANY MANDATED REGS AND PROCS WHILE MAINTAINING A CALM, PROFESSIONAL DEMEANOR IN THE COCKPIT. REGARDLESS OF THE ABOVE FACTORS AND CONSIDERATIONS, MY OPINION IS THAT THERE IS NO INST, DEVICE, OR GADGET CAN REPLACE AN AVIATOR'S SKILL AND JUDGEMENT. THIS OCCASION HAS ONLY REINFORCED MY BELIEF THAT A PLT'S BEST SAFETY DEVICE IS HIS/HER OWN TRAINING AND SELF-DISCIPLINE. SUPPLEMENTAL INFO FROM ACN 453712: CORRECTIVE ACTION FOR ME IS TO DEFINITELY INCREASE MY SITUATIONAL AWARENESS OF THE ACFT'S POS IN SPACE COMPARED TO THAT ASSIGNED, AND TO VERIFY CLRNCS FOR THE LDA OR VISUAL APCH. AND ALT CAPTURE FEATURE ON THE AUTOPLT WOULD HAVE PRECLUDED ANY PART OF THIS INCIDENT FROM OCCURRING. POSSIBLY SIMULTANEOUS RADIO XMISSIONS PRECLUDED US FROM COMMUNICATING OUR VISUAL ACQUISITION OF THE LOW TFC TO APCH CTL, OR FOR HIM ADVISING US TO CHK OUR ALT SOONER. THE ALT ALERT TONE FUNCTION (NOTIFYING PLTS WITHIN 300 FT APCHING A SELECTED ALT, AND PASSING 300 FT PAST A SELECTED ALT) SHOULD BE A CONTINUOUS TONE ONCE PAST THE SELECTED ALT TO PREVENT INADVERTENT ALTDEVS.

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.