TCASII saves the day again! Near midair collision avoided while 2 aircraft in proximity to clouds.

Attributes
ACN	219930
Time
Date	199208
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : bna
State Reference	TN
Altitude	msl bound lower : 4000 msl bound upper : 4600
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bna
Operator	common carrier : air carrier
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Navigation In Use	Other Other
Flight Phase	descent : approach other
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Small Aircraft
Flight Phase	descent other
Route In Use	enroute : direct
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 5000 flight time type : 200
ASRS Report	219930
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 : nmac inflight encounter : vfr in imc non adherence : far non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action
Consequence	Other
Miss Distance	horizontal : 0 vertical : 200
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I believe that in this case the TCASII may have helped in avoiding a possible midair collision. Although the traffic was never visually contacted, the situation we were in confirmed its authenticity. The cloud layer we were in was gradually sloping up in the direction of our flight. The aircraft in conflict was VFR because approach control finally pointed out unconfirmed traffic after we had begun deviation. I believe the aircraft was probably following the sloping cloud formation in his descent towards us and never saw us because of the thin layer of clouds we were in at 4000 ft. Approach had not yet pointed conflicting traffic out. Command to climb, climb! The copilot executed a climb from 4000 ft straight ahead traffic passed under on TCASII screen as approach control nervously pointed out unconfirmed traffic at 1 O'clock position.

Original NASA ASRS Text

Title: TCASII SAVES THE DAY AGAIN! NMAC AVOIDED WHILE 2 ACFT IN PROX TO CLOUDS.

Narrative: I BELIEVE THAT IN THIS CASE THE TCASII MAY HAVE HELPED IN AVOIDING A POSSIBLE MIDAIR COLLISION. ALTHOUGH THE TFC WAS NEVER VISUALLY CONTACTED, THE SITUATION WE WERE IN CONFIRMED ITS AUTHENTICITY. THE CLOUD LAYER WE WERE IN WAS GRADUALLY SLOPING UP IN THE DIRECTION OF OUR FLT. THE ACFT IN CONFLICT WAS VFR BECAUSE APCH CTL FINALLY POINTED OUT UNCONFIRMED TFC AFTER WE HAD BEGUN DEV. I BELIEVE THE ACFT WAS PROBABLY FOLLOWING THE SLOPING CLOUD FORMATION IN HIS DSCNT TOWARDS US AND NEVER SAW US BECAUSE OF THE THIN LAYER OF CLOUDS WE WERE IN AT 4000 FT. APCH HAD NOT YET POINTED CONFLICTING TFC OUT. COMMAND TO CLB, CLB! THE COPLT EXECUTED A CLB FROM 4000 FT STRAIGHT AHEAD TFC PASSED UNDER ON TCASII SCREEN AS APCH CTL NERVOUSLY POINTED OUT UNCONFIRMED TFC AT 1 O'CLOCK POS.

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.