TCASII logic problem.

Attributes
ACN	270640
Time
Date	199405
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : bib
State Reference	IL
Altitude	msl bound lower : 27000 msl bound upper : 28000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	climbout : intermediate altitude cruise other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 225 flight time total : 12500 flight time type : 8500
ASRS Report	270640
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe conflict : airborne less severe inflight encounter other non adherence : clearance non adherence : published procedure other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 18000 vertical : 800
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

While climbing eastbound out of stl about over bible grove, we had a TCASII TA while approaching FL270. As we leveled at FL270 we visually acquired a B-737 at FL280, we then received a TCASII RA to climb. Center asked us to verify level at FL270, which we did. We maintained a visual on the traffic B-737 at all times and observed what appeared to be a slow descent with a turn off course behind us. There was quite a bit of confusion on the radio at this point. During this entire evolution, our closest point of approach was about 3 mi. It later became apparent that our rate of climb may have triggered the TCASII warning in both aircraft. This other B-737 was a complete surprise to us when the TCASII went off. I feel that, had ATC pointed out this traffic prior to the TCASII warning, this would have been avoided. I am a firm believer in the TCASII system.

Original NASA ASRS Text

Title: TCASII LOGIC PROB.

Narrative: WHILE CLBING EBOUND OUT OF STL ABOUT OVER BIBLE GROVE, WE HAD A TCASII TA WHILE APCHING FL270. AS WE LEVELED AT FL270 WE VISUALLY ACQUIRED A B-737 AT FL280, WE THEN RECEIVED A TCASII RA TO CLB. CTR ASKED US TO VERIFY LEVEL AT FL270, WHICH WE DID. WE MAINTAINED A VISUAL ON THE TFC B-737 AT ALL TIMES AND OBSERVED WHAT APPEARED TO BE A SLOW DSCNT WITH A TURN OFF COURSE BEHIND US. THERE WAS QUITE A BIT OF CONFUSION ON THE RADIO AT THIS POINT. DURING THIS ENTIRE EVOLUTION, OUR CLOSEST POINT OF APCH WAS ABOUT 3 MI. IT LATER BECAME APPARENT THAT OUR RATE OF CLB MAY HAVE TRIGGERED THE TCASII WARNING IN BOTH ACFT. THIS OTHER B-737 WAS A COMPLETE SURPRISE TO US WHEN THE TCASII WENT OFF. I FEEL THAT, HAD ATC POINTED OUT THIS TFC PRIOR TO THE TCASII WARNING, THIS WOULD HAVE BEEN AVOIDED. I AM A FIRM BELIEVER IN THE TCASII SYS.

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.