Commuter mdt altitude deviation excursion from clearance altitude in response to TCASII RA.

Attributes
ACN	188623
Time
Date	199109
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : rfd
State Reference	IL
Altitude	msl bound lower : 3000 msl bound upper : 3300
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : rfd
Operator	common carrier : air carrier
Make Model Name	Medium Transport, High Wing, 2 Turboprop Eng
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : flight engineer pilot : commercial
Experience	flight time last 90 days : 150 flight time total : 2300
ASRS Report	188623
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	other

Narrative:

This was a TCASII situation where our aircraft was at 3000 ft MSL approaching rockford. TCAS 'traffic alert' activated which showed traffic at 10 O'clock and 2 mi. ATC (rfd approach) then advised us of traffic at 9-10 O'clock and 3 mi at 2500 ft. The visibility was approximately 1/4 mi (IMC) in haze. We responded with 'negative contact'. TCAS system them issued a resolution advisory indication an 1800 FPM climb was necessary to avoid a mid-air collision. The captain initiated a climb as I advised ATC we did not see the traffic and were climbing out of 3000 ft to avoid it. As we ascended to 3300 ft, TCAS showed traffic passed behind us by 1/2 mi. Then TCAS issued 'clear of conflict.' we descended back to 3000 ft and advised ATC. The TCASII system was required to be in our aircraft by the FAA and without visual contact we must obey the commands issued by TCASII. There becomes a definite conflict of information when ATC had verified an aircraft's altitude but TCAS sees it as a threat. Not all ATC facilities are informed on the parameters which cause TCASII to activate and therefore conflicts occur. We did call rockford approach facility and explain this to them immediately after the incident.

Original NASA ASRS Text

Title: COMMUTER MDT ALT DEV EXCURSION FROM CLRNC ALT IN RESPONSE TO TCASII RA.

Narrative: THIS WAS A TCASII SITUATION WHERE OUR ACFT WAS AT 3000 FT MSL APCHING ROCKFORD. TCAS 'TFC ALERT' ACTIVATED WHICH SHOWED TFC AT 10 O'CLOCK AND 2 MI. ATC (RFD APCH) THEN ADVISED US OF TFC AT 9-10 O'CLOCK AND 3 MI AT 2500 FT. THE VISIBILITY WAS APPROX 1/4 MI (IMC) IN HAZE. WE RESPONDED WITH 'NEGATIVE CONTACT'. TCAS SYS THEM ISSUED A RESOLUTION ADVISORY INDICATION AN 1800 FPM CLB WAS NECESSARY TO AVOID A MID-AIR COLLISION. THE CAPT INITIATED A CLB AS I ADVISED ATC WE DID NOT SEE THE TFC AND WERE CLBING OUT OF 3000 FT TO AVOID IT. AS WE ASCENDED TO 3300 FT, TCAS SHOWED TFC PASSED BEHIND US BY 1/2 MI. THEN TCAS ISSUED 'CLR OF CONFLICT.' WE DSNDED BACK TO 3000 FT AND ADVISED ATC. THE TCASII SYS WAS REQUIRED TO BE IN OUR ACFT BY THE FAA AND WITHOUT VISUAL CONTACT WE MUST OBEY THE COMMANDS ISSUED BY TCASII. THERE BECOMES A DEFINITE CONFLICT OF INFO WHEN ATC HAD VERIFIED AN ACFT'S ALT BUT TCAS SEES IT AS A THREAT. NOT ALL ATC FACILITIES ARE INFORMED ON THE PARAMETERS WHICH CAUSE TCASII TO ACTIVATE AND THEREFORE CONFLICTS OCCUR. WE DID CALL ROCKFORD APCH FACILITY AND EXPLAIN THIS TO THEM IMMEDIATELY AFTER THE INCIDENT.

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.