In holding received TCASII RA to descend.

Attributes
ACN	198927
Time
Date	199201
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : den
State Reference	CO
Altitude	msl bound lower : 20000 msl bound upper : 20000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdv tower : tus
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	other
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	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 : 180
ASRS Report	198927
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While holding at smity international, we received a TA 'traffic, traffic' followed a few seconds later by an RA 'descend, now, descend.' we were level at FL200. We were watching the TCASII screen as we saw a target immediately above us descending out of FL215. Our choices were to 1) ignore the RA, or 2) descend as commanded following the ivsi. There was another (3RD) airplane at FL190. Because I was fearful the airplane above was going to descend through FL210 and down on top of us and because I determined the traffic at FL190 was spaced adequately in horizontal distance, I told the first officer to begin a descent. We immediately informed ZDV. At FL195 the RA silenced and ZDV reclred us to FL200. By watching the TCASII screen we determined that the airplane above was level at FL210 and we climbed back to FL200. The second airplane (one of our medium large transport's) said his TCASII was 'acting up' also. We did not write up the TCASII system because we believed it worked as designed: either the rate of descent of the airplane above caused the alarm or perhaps the proximity of our aircraft. The TCASII system also worked well before and after this incident.

Original NASA ASRS Text

Title: IN HOLDING RECEIVED TCASII RA TO DSND.

Narrative: WHILE HOLDING AT SMITY INTL, WE RECEIVED A TA 'TFC, TFC' FOLLOWED A FEW SECONDS LATER BY AN RA 'DSND, NOW, DSND.' WE WERE LEVEL AT FL200. WE WERE WATCHING THE TCASII SCREEN AS WE SAW A TARGET IMMEDIATELY ABOVE US DSNDING OUT OF FL215. OUR CHOICES WERE TO 1) IGNORE THE RA, OR 2) DSND AS COMMANDED FOLLOWING THE IVSI. THERE WAS ANOTHER (3RD) AIRPLANE AT FL190. BECAUSE I WAS FEARFUL THE AIRPLANE ABOVE WAS GOING TO DSND THROUGH FL210 AND DOWN ON TOP OF US AND BECAUSE I DETERMINED THE TFC AT FL190 WAS SPACED ADEQUATELY IN HORIZ DISTANCE, I TOLD THE FO TO BEGIN A DSCNT. WE IMMEDIATELY INFORMED ZDV. AT FL195 THE RA SILENCED AND ZDV RECLRED US TO FL200. BY WATCHING THE TCASII SCREEN WE DETERMINED THAT THE AIRPLANE ABOVE WAS LEVEL AT FL210 AND WE CLBED BACK TO FL200. THE SECOND AIRPLANE (ONE OF OUR MLG'S) SAID HIS TCASII WAS 'ACTING UP' ALSO. WE DID NOT WRITE UP THE TCASII SYS BECAUSE WE BELIEVED IT WORKED AS DESIGNED: EITHER THE RATE OF DSCNT OF THE AIRPLANE ABOVE CAUSED THE ALARM OR PERHAPS THE PROX OF OUR ACFT. THE TCASII SYS ALSO WORKED WELL BEFORE AND AFTER THIS 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.