Air carrier X aircraft equipment problem transponder mode C received TCASII RA from air carrier Y.

Attributes
ACN	224265
Time
Date	199210
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : dny
State Reference	NY
Altitude	msl bound lower : 20000 msl bound upper : 21000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zbw
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Transport, Low Wing, 2 Turboprop Eng
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
ASRS Report	224265
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe conflict : airborne less severe
Independent Detector	other controllera other flight crewa
Resolutory Action	aircraft : equipment problem dissipated controller : issued new clearance
Consequence	faa : investigated
Miss Distance	horizontal : 6000 vertical : 1000
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Air carrier X flight planned alb-dny-lhy, level FL260 descended to FL210. Air carrier Y flight planned swf-dny-uca level at FL200. Air carrier X was descended to meet crossing restriction 50 northeast avp at FL180 with intermediate level off above air carrier Y. When I observed air carrier X descending through 20700 5 mi north of air carrier Y and converging, I said 'say altitude.' air carrier X responded 'FL210, boston we have a TCASII RA and we need to climb. The air carrier Y altitude was FL200, so I asked, 'verify assigned altitude.' air carrier X whose mode C now read 20300 said 'FL210, boston we need to climb now.' I replied 'roger climb and maintain FL210.' I then observed the data block of air carrier X read FL210. The agency called this event a mode C problem non occurrence. The TCASII RA resulting from a malfunctioning mode C. Event was very confusing, aircraft passed within 1 mi of each other.

Original NASA ASRS Text

Title: ACR X ACFT EQUIP PROBLEM TRANSPONDER MODE C RECEIVED TCASII RA FROM ACR Y.

Narrative: ACR X FLT PLANNED ALB-DNY-LHY, LEVEL FL260 DSNDED TO FL210. ACR Y FLT PLANNED SWF-DNY-UCA LEVEL AT FL200. ACR X WAS DSNDED TO MEET XING RESTRICTION 50 NE AVP AT FL180 WITH INTERMEDIATE LEVEL OFF ABOVE ACR Y. WHEN I OBSERVED ACR X DSNDING THROUGH 20700 5 MI N OF ACR Y AND CONVERGING, I SAID 'SAY ALT.' ACR X RESPONDED 'FL210, BOSTON WE HAVE A TCASII RA AND WE NEED TO CLB. THE ACR Y ALT WAS FL200, SO I ASKED, 'VERIFY ASSIGNED ALT.' ACR X WHOSE MODE C NOW READ 20300 SAID 'FL210, BOSTON WE NEED TO CLB NOW.' I REPLIED 'ROGER CLB AND MAINTAIN FL210.' I THEN OBSERVED THE DATA BLOCK OF ACR X READ FL210. THE AGENCY CALLED THIS EVENT A MODE C PROBLEM NON OCCURRENCE. THE TCASII RA RESULTING FROM A MALFUNCTIONING MODE C. EVENT WAS VERY CONFUSING, ACFT PASSED WITHIN 1 MI OF EACH OTHER.

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.