Altitude deviation due to TCASII RA.

Attributes
ACN	234188
Time
Date	199302
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : bvt
State Reference	IN
Altitude	msl bound lower : 25400 msl bound upper : 26000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : cfi pilot : flight engineer
Experience	flight time last 90 days : 150 flight time total : 9900 flight time type : 1000
ASRS Report	234188
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : took evasive action
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 4500 vertical : 600
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

We were level at FL260 in the clouds en route direct boiler (bvt) VOR. ZID (133.05) issued us traffic at 11 O'clock descending to FL270. We both looked at the TCASII scope, and saw the traffic showing a plus 12 descending. It then went to a plus 11 descending, plus 10 descending, plus 9 descending and still descending. I told the first officer if it got to a plus 800 to ask the center what was happening. We then got the aural warning 'traffic, traffic.' the first officer started to call the center when we got 'descend, descend.' I disengaged the autoplt and nosed over to keep out of the red arc on the ivsi. The first officer notified center we were descending to a TCASII RA. The next aural warning was monitor descent and then eventually clear of traffic. We then climbed back up to our assigned altitude FL260. During this RA, the closest we noticed the other aircraft was at plus 600 ft, we had descended down to 25400 ft during the RA and the first officer said that at 25400 ft, she noticed the target on the TCASII scope was now at plus 1400 and showing a climb. Once we were level, we asked the center again if they understood we descended due to a TCASII RA and they said yes. They also said they had no problem with it. On the next ZID frequency the controller or supervisor asked us if we had responded to an RA on the previous frequency and we said yes. I then spoke with our dispatch and told them what had occurred and asked them to talk with ZID and find out what they saw. I called dispatch once we were on the ground and they said they spoke with the supervisor at ZID. I believe the dispatcher said that the center had shown the other flight within 600 ft of us, however, the other flight said they were level at 27000 ft the whole time. I am a new captain in the aircraft and have been with the airline for 7 yrs. We followed the procedure exactly as we were taught and believe TCASII to be a very valuable tool in preventing midair collisions. Even though we never saw the other aircraft I am convinced it prevented a near tragic incident.

Original NASA ASRS Text

Title: ALTDEV DUE TO TCASII RA.

Narrative: WE WERE LEVEL AT FL260 IN THE CLOUDS ENRTE DIRECT BOILER (BVT) VOR. ZID (133.05) ISSUED US TFC AT 11 O'CLOCK DSNDING TO FL270. WE BOTH LOOKED AT THE TCASII SCOPE, AND SAW THE TFC SHOWING A PLUS 12 DSNDING. IT THEN WENT TO A PLUS 11 DSNDING, PLUS 10 DSNDING, PLUS 9 DSNDING AND STILL DSNDING. I TOLD THE FO IF IT GOT TO A PLUS 800 TO ASK THE CTR WHAT WAS HAPPENING. WE THEN GOT THE AURAL WARNING 'TFC, TFC.' THE FO STARTED TO CALL THE CTR WHEN WE GOT 'DSND, DSND.' I DISENGAGED THE AUTOPLT AND NOSED OVER TO KEEP OUT OF THE RED ARC ON THE IVSI. THE FO NOTIFIED CTR WE WERE DSNDING TO A TCASII RA. THE NEXT AURAL WARNING WAS MONITOR DSCNT AND THEN EVENTUALLY CLR OF TFC. WE THEN CLBED BACK UP TO OUR ASSIGNED ALT FL260. DURING THIS RA, THE CLOSEST WE NOTICED THE OTHER ACFT WAS AT PLUS 600 FT, WE HAD DSNDED DOWN TO 25400 FT DURING THE RA AND THE FO SAID THAT AT 25400 FT, SHE NOTICED THE TARGET ON THE TCASII SCOPE WAS NOW AT PLUS 1400 AND SHOWING A CLB. ONCE WE WERE LEVEL, WE ASKED THE CTR AGAIN IF THEY UNDERSTOOD WE DSNDED DUE TO A TCASII RA AND THEY SAID YES. THEY ALSO SAID THEY HAD NO PROB WITH IT. ON THE NEXT ZID FREQ THE CTLR OR SUPVR ASKED US IF WE HAD RESPONDED TO AN RA ON THE PREVIOUS FREQ AND WE SAID YES. I THEN SPOKE WITH OUR DISPATCH AND TOLD THEM WHAT HAD OCCURRED AND ASKED THEM TO TALK WITH ZID AND FIND OUT WHAT THEY SAW. I CALLED DISPATCH ONCE WE WERE ON THE GND AND THEY SAID THEY SPOKE WITH THE SUPVR AT ZID. I BELIEVE THE DISPATCHER SAID THAT THE CTR HAD SHOWN THE OTHER FLT WITHIN 600 FT OF US, HOWEVER, THE OTHER FLT SAID THEY WERE LEVEL AT 27000 FT THE WHOLE TIME. I AM A NEW CAPT IN THE ACFT AND HAVE BEEN WITH THE AIRLINE FOR 7 YRS. WE FOLLOWED THE PROC EXACTLY AS WE WERE TAUGHT AND BELIEVE TCASII TO BE A VERY VALUABLE TOOL IN PREVENTING MIDAIR COLLISIONS. EVEN THOUGH WE NEVER SAW THE OTHER ACFT I AM CONVINCED IT PREVENTED A NEAR TRAGIC INCIDENT.

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.