Altitude deviation. Aircraft equipment problem.

Attributes
ACN	292261
Time
Date	199412
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : bos
State Reference	MA
Altitude	msl bound lower : 5600 msl bound upper : 5600
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bos
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent other
Route In Use	enroute : direct
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Flight Plan	VFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : atp pilot : cfi pilot : commercial
Experience	flight time last 90 days : 170 flight time total : 4100 flight time type : 2600
ASRS Report	292261
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : provided flight assist flight crew : took evasive action other
Consequence	Other
Supplementary
Primary Problem	Aircraft

Narrative:

TCASII gave a duel presentation of a C172. Both targets indicated the same altitude throughout the event. ATC was contacted prior to RA, pointed out traffic at 10 O'clock 3 mi. TCASII had target at 5500 ft, minus 100 ft from us, at 3 and 1 mi. The 1 mi target caused an RA climb and increase climb command and ATC was notified and informed us that C172 was VFR and 3 mi, thus no loss of ATC separation.

Original NASA ASRS Text

Title: ALTDEV. ACFT EQUIP PROB.

Narrative: TCASII GAVE A DUEL PRESENTATION OF A C172. BOTH TARGETS INDICATED THE SAME ALT THROUGHOUT THE EVENT. ATC WAS CONTACTED PRIOR TO RA, POINTED OUT TFC AT 10 O'CLOCK 3 MI. TCASII HAD TARGET AT 5500 FT, MINUS 100 FT FROM US, AT 3 AND 1 MI. THE 1 MI TARGET CAUSED AN RA CLB AND INCREASE CLB COMMAND AND ATC WAS NOTIFIED AND INFORMED US THAT C172 WAS VFR AND 3 MI, THUS NO LOSS OF ATC SEPARATION.

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.