Altitude excursion below the class B of atl for a TCASII TA with no altitude indication.

Attributes
ACN	489920
Time
Date	200010
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : atl.vortac
State Reference	GA
Altitude	msl bound lower : 4000 msl bound upper : 4350
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : atl.tracon
Operator	common carrier : air carrier
Make Model Name	Brasilia EMB-120 All Series
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Aircraft 2
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	other
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 220 flight time total : 2330 flight time type : 1500
ASRS Report	489920
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance
Independent Detector	aircraft equipment : tcas
Resolutory Action	flight crew : took precautionary avoidance action
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance Aircraft
Primary Problem	Flight Crew Human Performance

Narrative:

We departed atlanta en route to macon, GA. We were at an intermediate leveloff altitude of 4000 ft MSL. We were talking to approach control. Controller was very busy with traffic. I was PF. The PNF was performing checklists and getting the ATIS for macon, GA. I saw a target on TCASII converging from 10 NM from 11 O'clock position. I interrupted the PNF to help me look for traffic. The sky condition was very hazy, approximately 5 SM. There was no altitude next to target. I assume his mode C was turned off. Approach control was talking non-stop to other traffic. I tried to break in to query about traffic. We got a 'traffic traffic' alert. I could see up and ahead best. We climbed to 4350 ft MSL. I alerted approach that we were deviating altitude for traffic. No response. We saw target pass behind us on TCASII and descended back to 4000 ft MSL. I then queried ATC again about traffic. Approach said they had no traffic for us. We continued to watch traffic pass behind us for 20 NM on TCASII. No further incident. The target never did show an altitude. Never got a visual on traffic.

Original NASA ASRS Text

Title: ALT EXCURSION BELOW THE CLASS B OF ATL FOR A TCASII TA WITH NO ALT INDICATION.

Narrative: WE DEPARTED ATLANTA ENRTE TO MACON, GA. WE WERE AT AN INTERMEDIATE LEVELOFF ALT OF 4000 FT MSL. WE WERE TALKING TO APCH CTL. CTLR WAS VERY BUSY WITH TFC. I WAS PF. THE PNF WAS PERFORMING CHKLISTS AND GETTING THE ATIS FOR MACON, GA. I SAW A TARGET ON TCASII CONVERGING FROM 10 NM FROM 11 O'CLOCK POS. I INTERRUPTED THE PNF TO HELP ME LOOK FOR TFC. THE SKY CONDITION WAS VERY HAZY, APPROX 5 SM. THERE WAS NO ALT NEXT TO TARGET. I ASSUME HIS MODE C WAS TURNED OFF. APCH CTL WAS TALKING NON-STOP TO OTHER TFC. I TRIED TO BREAK IN TO QUERY ABOUT TFC. WE GOT A 'TFC TFC' ALERT. I COULD SEE UP AND AHEAD BEST. WE CLBED TO 4350 FT MSL. I ALERTED APCH THAT WE WERE DEVIATING ALT FOR TFC. NO RESPONSE. WE SAW TARGET PASS BEHIND US ON TCASII AND DSNDED BACK TO 4000 FT MSL. I THEN QUERIED ATC AGAIN ABOUT TFC. APCH SAID THEY HAD NO TFC FOR US. WE CONTINUED TO WATCH TFC PASS BEHIND US FOR 20 NM ON TCASII. NO FURTHER INCIDENT. THE TARGET NEVER DID SHOW AN ALT. NEVER GOT A VISUAL ON TFC.

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.