Air carrier X TCASII RA from aircraft with erroneous transponder mode C.

Attributes
ACN	242175
Time
Date	199305
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : olm
State Reference	WA
Altitude	msl bound lower : 10400 msl bound upper : 10400
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : sea
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	descent 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	242175
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Air carrier X inbound to seattle on the olympic STAR to land runway 34R. Controller is told by pilot of air carrier X that he had received an RA, and the controller issued the only traffic near him at 3500 ft. Immediately thereafter, the unidented aircraft's mode C showed 10300 ft. Continued observation of the unidented aircraft's mode C shows alternating mode C of between 3500 ft and 10300 ft. We believe that this was the same aircraft that had caused an RA on another air carrier X aircraft earlier in the day.

Original NASA ASRS Text

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

Narrative: ACR X INBOUND TO SEATTLE ON THE OLYMPIC STAR TO LAND RWY 34R. CTLR IS TOLD BY PLT OF ACR X THAT HE HAD RECEIVED AN RA, AND THE CTLR ISSUED THE ONLY TFC NEAR HIM AT 3500 FT. IMMEDIATELY THEREAFTER, THE UNIDENTED ACFT'S MODE C SHOWED 10300 FT. CONTINUED OBSERVATION OF THE UNIDENTED ACFT'S MODE C SHOWS ALTERNATING MODE C OF BTWN 3500 FT AND 10300 FT. WE BELIEVE THAT THIS WAS THE SAME ACFT THAT HAD CAUSED AN RA ON ANOTHER ACR X ACFT EARLIER IN THE DAY.

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.