Air carrier X TCASII RA climb from aircraft with erroneous transponder.

Attributes
ACN	242174
Time
Date	199305
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : sea
State Reference	WA
Altitude	msl bound lower : 11000 msl bound upper : 11000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : sea
Operator	common carrier : air carrier
Make Model Name	Widebody, Low Wing, 3 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other
Route In Use	arrival star : star
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller military : 3 controller radar : 11
ASRS Report	242174
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Air carrier X inbound to seattle tacoma airport on the chins STAR to land runway 34R. Controller turns air carrier X for vectors visual approach. Controller issues traffic at 2 O'clock observed at 10300 mode C. During the transmission, the unidentified aircraft Y mode C went to 3500 and air carrier X was told of his altitude. The pilot responded that he had received an RA and was climbing. Air carrier X never saw the traffic, and further observation of the unidentified aircraft Y showed his mode C alternate between 3500 and 10300 ft. This is the second such occurrence between TCASII equipped aircraft and an unidentified aircraft with a fluctuating mode C. These 2 aircraft were never in conflict.

Original NASA ASRS Text

Title: ACR X TCASII RA CLB FROM ACFT WITH ERRONEOUS XPONDER.

Narrative: ACR X INBOUND TO SEATTLE TACOMA ARPT ON THE CHINS STAR TO LAND RWY 34R. CTLR TURNS ACR X FOR VECTORS VISUAL APCH. CTLR ISSUES TFC AT 2 O'CLOCK OBSERVED AT 10300 MODE C. DURING THE XMISSION, THE UNIDENTIFIED ACFT Y MODE C WENT TO 3500 AND ACR X WAS TOLD OF HIS ALT. THE PLT RESPONDED THAT HE HAD RECEIVED AN RA AND WAS CLBING. ACR X NEVER SAW THE TFC, AND FURTHER OBSERVATION OF THE UNIDENTIFIED ACFT Y SHOWED HIS MODE C ALTERNATE BTWN 3500 AND 10300 FT. THIS IS THE SECOND SUCH OCCURRENCE BTWN TCASII EQUIPPED ACFT AND AN UNIDENTIFIED ACFT WITH A FLUCTUATING MODE C. THESE 2 ACFT WERE NEVER IN CONFLICT.

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.