Possible conflict.

Attributes
ACN	266062
Time
Date	199403
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : den
State Reference	CO
Altitude	msl bound lower : 17000 msl bound upper : 17700
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival other arrival star : star enroute airway : zdv
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	other : unknown
Flight Phase	climbout : intermediate altitude
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 60 flight time total : 8000
ASRS Report	266062
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 30 flight time total : 3000
ASRS Report	266312
Events
Anomaly	altitude deviation : crossing restriction not met non adherence : clearance non adherence : far other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 500
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

My aircraft B-737-300 flight en route from bur to den on mar/xx/94. I was cleared for the profile descent into den with the 250 KT airspeed constraint at byson intersection removed. I informed ZDV that I intended to maintain 300 KTS in my descent until reaching byson at 17000 ft. ATC concurred. When approaching byson, ZDV informed me of slow moving swbound traffic at 15200 ft north a climb in my 11 O'clock position. Since I could not immediately see the target, I expanded the range scale on my HSI TCASII presentation to give me a better picture of the developing situation. I indicated to ZDV that I had the target on TCASII, it was still climbing southwest toward byson as we continued our autoflt VNAV descent, finally the TCASII TA warning alerted us just as we started a turn to the right to avoid a rapidly developing altitude conflict. As the TA/RA alert was sounded by our equipment, and we immediately responded with the nose up conflict resolution, the aircraft was spotted to our left in our 10:30 position, at our altitude, quite close to us. TCASII may have saved us from a midair. During the flash moment that I was able to observe the aircraft, I saw it to be a high wing, multi-engine propeller. Our TCASII deviation caused us to climb 600-700 ft, thereby breaking the altitude constraint at byson. TCASII did what it was designed to do. The remainder of the flight was uneventful with a safe landing at den. I perceived the 'slow moving' aircraft to also be slow climbing. Wrong. The fellow was obviously a turbine pwred aircraft. Because he was climbing much faster than I thought. This whole scenario took place in about 1 min. I also forgot to factor in the delay on the TCASII display for position and altitude. To add to the confusion, I had experienced a TCASII arrival into bur the previous day (a sunday) with numerous small TCASII targets with minimal performance demonstrated. The experience lulled me into thinking 'slow moving' also meant slow climb performance.

Original NASA ASRS Text

Title: POSSIBLE CONFLICT.

Narrative: MY ACFT B-737-300 FLT ENRTE FROM BUR TO DEN ON MAR/XX/94. I WAS CLRED FOR THE PROFILE DSCNT INTO DEN WITH THE 250 KT AIRSPD CONSTRAINT AT BYSON INTXN REMOVED. I INFORMED ZDV THAT I INTENDED TO MAINTAIN 300 KTS IN MY DSCNT UNTIL REACHING BYSON AT 17000 FT. ATC CONCURRED. WHEN APCHING BYSON, ZDV INFORMED ME OF SLOW MOVING SWBOUND TFC AT 15200 FT N A CLB IN MY 11 O'CLOCK POS. SINCE I COULD NOT IMMEDIATELY SEE THE TARGET, I EXPANDED THE RANGE SCALE ON MY HSI TCASII PRESENTATION TO GIVE ME A BETTER PICTURE OF THE DEVELOPING SIT. I INDICATED TO ZDV THAT I HAD THE TARGET ON TCASII, IT WAS STILL CLBING SW TOWARD BYSON AS WE CONTINUED OUR AUTOFLT VNAV DSCNT, FINALLY THE TCASII TA WARNING ALERTED US JUST AS WE STARTED A TURN TO THE R TO AVOID A RAPIDLY DEVELOPING ALT CONFLICT. AS THE TA/RA ALERT WAS SOUNDED BY OUR EQUIP, AND WE IMMEDIATELY RESPONDED WITH THE NOSE UP CONFLICT RESOLUTION, THE ACFT WAS SPOTTED TO OUR L IN OUR 10:30 POS, AT OUR ALT, QUITE CLOSE TO US. TCASII MAY HAVE SAVED US FROM A MIDAIR. DURING THE FLASH MOMENT THAT I WAS ABLE TO OBSERVE THE ACFT, I SAW IT TO BE A HIGH WING, MULTI-ENG PROP. OUR TCASII DEV CAUSED US TO CLB 600-700 FT, THEREBY BREAKING THE ALT CONSTRAINT AT BYSON. TCASII DID WHAT IT WAS DESIGNED TO DO. THE REMAINDER OF THE FLT WAS UNEVENTFUL WITH A SAFE LNDG AT DEN. I PERCEIVED THE 'SLOW MOVING' ACFT TO ALSO BE SLOW CLBING. WRONG. THE FELLOW WAS OBVIOUSLY A TURBINE PWRED ACFT. BECAUSE HE WAS CLBING MUCH FASTER THAN I THOUGHT. THIS WHOLE SCENARIO TOOK PLACE IN ABOUT 1 MIN. I ALSO FORGOT TO FACTOR IN THE DELAY ON THE TCASII DISPLAY FOR POS AND ALT. TO ADD TO THE CONFUSION, I HAD EXPERIENCED A TCASII ARR INTO BUR THE PREVIOUS DAY (A SUNDAY) WITH NUMEROUS SMALL TCASII TARGETS WITH MINIMAL PERFORMANCE DEMONSTRATED. THE EXPERIENCE LULLED ME INTO THINKING 'SLOW MOVING' ALSO MEANT SLOW CLB PERFORMANCE.

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.