Potential conflict avoided after flight crew observation of conflicting traffic on TCASII.

Attributes
ACN	305060
Time
Date	199505
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : den
State Reference	CO
Altitude	msl bound lower : 9000 msl bound upper : 10000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : den
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : approach descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : approach descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : commercial pilot : cfi pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 120 flight time total : 12000 flight time type : 1300
ASRS Report	305060
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe inflight encounter : weather non adherence : required legal separation non adherence : clearance other spatial deviation
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	controller : issued new clearance flight crew : exited adverse environment
Consequence	Other
Miss Distance	vertical : 900
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Pilot Deviation
Situations
ATC Facility	procedure or policy : unspecified

Narrative:

During arrival to den we were given radar vectors to runway 17R where triple ILS's were being performed to the south. During approach we continually read back all headings and altitudes that were assigned. We were given a descent which we confirmed but as we proceeded, it appeared to be through another air carrier airplane's (with similar call sign) altitude. As we neared the localizer, it appeared (through observing our TCASII) as though he, too, was intercepting the same localizer and was extremely close. We attempted several times to get a word to approach who by now was even busier than before. At a point where we were within approximately 800-1000 ft vertical of our opposing traffic, we stopped our descent. We finally were able to get a hold of approach, whereupon being notified of our predicament, gave us an immediate climb and radar vector. As we began our climb and turn, we broke out of the clouds and saw our opposing traffic. The flight continued without incident to the airport. Traffic was very busy at this time. Thunderstorms were in the area with rain falling at the airport. The new approach system at den does a lot to reduce delays, but it appears when the area becomes saturated, a better plan for conflict would be in order. TCASII is a great tool but it too has a long way to go in interpretation in a very busy environment.

Original NASA ASRS Text

Title: POTENTIAL CONFLICT AVOIDED AFTER FLC OBSERVATION OF CONFLICTING TFC ON TCASII.

Narrative: DURING ARR TO DEN WE WERE GIVEN RADAR VECTORS TO RWY 17R WHERE TRIPLE ILS'S WERE BEING PERFORMED TO THE S. DURING APCH WE CONTINUALLY READ BACK ALL HDGS AND ALTS THAT WERE ASSIGNED. WE WERE GIVEN A DSCNT WHICH WE CONFIRMED BUT AS WE PROCEEDED, IT APPEARED TO BE THROUGH ANOTHER ACR AIRPLANE'S (WITH SIMILAR CALL SIGN) ALT. AS WE NEARED THE LOC, IT APPEARED (THROUGH OBSERVING OUR TCASII) AS THOUGH HE, TOO, WAS INTERCEPTING THE SAME LOC AND WAS EXTREMELY CLOSE. WE ATTEMPTED SEVERAL TIMES TO GET A WORD TO APCH WHO BY NOW WAS EVEN BUSIER THAN BEFORE. AT A POINT WHERE WE WERE WITHIN APPROX 800-1000 FT VERT OF OUR OPPOSING TFC, WE STOPPED OUR DSCNT. WE FINALLY WERE ABLE TO GET A HOLD OF APCH, WHEREUPON BEING NOTIFIED OF OUR PREDICAMENT, GAVE US AN IMMEDIATE CLB AND RADAR VECTOR. AS WE BEGAN OUR CLB AND TURN, WE BROKE OUT OF THE CLOUDS AND SAW OUR OPPOSING TFC. THE FLT CONTINUED WITHOUT INCIDENT TO THE ARPT. TFC WAS VERY BUSY AT THIS TIME. TSTMS WERE IN THE AREA WITH RAIN FALLING AT THE ARPT. THE NEW APCH SYS AT DEN DOES A LOT TO REDUCE DELAYS, BUT IT APPEARS WHEN THE AREA BECOMES SATURATED, A BETTER PLAN FOR CONFLICT WOULD BE IN ORDER. TCASII IS A GREAT TOOL BUT IT TOO HAS A LONG WAY TO GO IN INTERP IN A VERY BUSY ENVIRONMENT.

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.