A320 flight crew has TCASII alert. Climbs until clear indication. Evasive action climb.

Attributes
ACN	341140
Time
Date	199607
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : pdz
State Reference	CA
Altitude	msl bound lower : 8200 msl bound upper : 11100
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : sna
Operator	common carrier : air carrier
Make Model Name	A320
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival : profile descent
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 270 flight time total : 11000 flight time type : 300
ASRS Report	341140
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 : airborne less severe other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : took evasive action none taken : anomaly accepted
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Descent profile. Dawna intersection to kayoh intersection for orange county airport. Descending to 8000 ft. Given TA by socal, our 2 O'clock, 7 NM, at 7500 ft MSL (light aircraft). Socal then called traffic to ask why off altitude (mode C showed climbing to 9500 ft). Contact stated was level 7500 ft, must be mode C problem. Moments later we received TCASII RA. We did not have visual on contact. Immediately climbed at 2500 FPM to solution level at 11100 ft MSL. Descended when clear. Even though I knew the probable cause of this action (ie, faulty mode C on light aircraft). I could not help but think that this could be an intentional mode C IFF failure and someone trying to take out a scheduled jet airliner in a terminal area. Company policy requires mandatory compliance with RA but I feel the threat of someone intentional is real.

Original NASA ASRS Text

Title: A320 FLC HAS TCASII ALERT. CLBS UNTIL CLR INDICATION. EVASIVE ACTION CLB.

Narrative: DSCNT PROFILE. DAWNA INTXN TO KAYOH INTXN FOR ORANGE COUNTY ARPT. DSNDING TO 8000 FT. GIVEN TA BY SOCAL, OUR 2 O'CLOCK, 7 NM, AT 7500 FT MSL (LIGHT ACFT). SOCAL THEN CALLED TFC TO ASK WHY OFF ALT (MODE C SHOWED CLBING TO 9500 FT). CONTACT STATED WAS LEVEL 7500 FT, MUST BE MODE C PROB. MOMENTS LATER WE RECEIVED TCASII RA. WE DID NOT HAVE VISUAL ON CONTACT. IMMEDIATELY CLBED AT 2500 FPM TO SOLUTION LEVEL AT 11100 FT MSL. DSNDED WHEN CLR. EVEN THOUGH I KNEW THE PROBABLE CAUSE OF THIS ACTION (IE, FAULTY MODE C ON LIGHT ACFT). I COULD NOT HELP BUT THINK THAT THIS COULD BE AN INTENTIONAL MODE C IFF FAILURE AND SOMEONE TRYING TO TAKE OUT A SCHEDULED JET AIRLINER IN A TERMINAL AREA. COMPANY POLICY REQUIRES MANDATORY COMPLIANCE WITH RA BUT I FEEL THE THREAT OF SOMEONE INTENTIONAL IS REAL.

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.