E120 crew had altitude deviation.

Attributes
ACN	463860
Time
Date	200002
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : iah.airport
State Reference	TX
Altitude	msl bound lower : 2000 msl bound upper : 6000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Brasilia EMB-120 All Series
Operating Under FAR Part	Part 121
Flight Phase	descent : vacating altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 145 flight time total : 3150 flight time type : 195
ASRS Report	463860
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : commercial pilot : instrument
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued alert controller : issued new clearance
Supplementary
Problem Areas	Flight Crew Human Performance FAA Airspace Structure ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were operating as air carrier flight abcd from laredo, tx. We were on a downwind vector expecting a landing on runway 27 at iah. Our altitude assigned was 6000 ft. We were told to contact a second approach frequency, but were unable to check in due to frequency congestion. Many xmissions were being blocked. As pilot read back their instructions, the controller would end up blocking their readbacks with other aircraft instructions. Without being able to check-in both myself and the first officer heard instructions for different air carrier abcd to descend and maintain 2000 ft. The first officer read back the clearance, but was blocked by the controller saying to turn 360 degree heading. The first officer then read back down to 2000 ft and turning 360 degrees. Not knowing that the readback was blocked by the controller or another aircraft, we commenced the descent and turn. As we were northbound descending through around 4500 ft, the controller called us and told us to turn right 180 degrees and maintain 4000 ft. I immediately started the turn. In the turn the controller told us to tighten the turn in which we did. At this time I asked the controller what was going on since we were cleared to 2000 ft and heading 360 degrees. He came back and said it was for a different air carrier flight. After that we were vectored for the approach and landed uneventful. The radio frequency being very congested and unable to read back instructions without being blocked by the controller or other aircraft were the contributing factors leading to this.

Original NASA ASRS Text

Title: E120 CREW HAD ALTDEV.

Narrative: WE WERE OPERATING AS ACR FLT ABCD FROM LAREDO, TX. WE WERE ON A DOWNWIND VECTOR EXPECTING A LNDG ON RWY 27 AT IAH. OUR ALT ASSIGNED WAS 6000 FT. WE WERE TOLD TO CONTACT A SECOND APCH FREQ, BUT WERE UNABLE TO CHK IN DUE TO FREQ CONGESTION. MANY XMISSIONS WERE BEING BLOCKED. AS PLT READ BACK THEIR INSTRUCTIONS, THE CTLR WOULD END UP BLOCKING THEIR READBACKS WITH OTHER ACFT INSTRUCTIONS. WITHOUT BEING ABLE TO CHK-IN BOTH MYSELF AND THE FO HEARD INSTRUCTIONS FOR DIFFERENT ACR ABCD TO DSND AND MAINTAIN 2000 FT. THE FO READ BACK THE CLRNC, BUT WAS BLOCKED BY THE CTLR SAYING TO TURN 360 DEG HDG. THE FO THEN READ BACK DOWN TO 2000 FT AND TURNING 360 DEGS. NOT KNOWING THAT THE READBACK WAS BLOCKED BY THE CTLR OR ANOTHER ACFT, WE COMMENCED THE DSCNT AND TURN. AS WE WERE NBOUND DSNDING THROUGH AROUND 4500 FT, THE CTLR CALLED US AND TOLD US TO TURN R 180 DEGS AND MAINTAIN 4000 FT. I IMMEDIATELY STARTED THE TURN. IN THE TURN THE CTLR TOLD US TO TIGHTEN THE TURN IN WHICH WE DID. AT THIS TIME I ASKED THE CTLR WHAT WAS GOING ON SINCE WE WERE CLRED TO 2000 FT AND HEADING 360 DEGS. HE CAME BACK AND SAID IT WAS FOR A DIFFERENT ACR FLT. AFTER THAT WE WERE VECTORED FOR THE APCH AND LANDED UNEVENTFUL. THE RADIO FREQ BEING VERY CONGESTED AND UNABLE TO READ BACK INSTRUCTIONS WITHOUT BEING BLOCKED BY THE CTLR OR OTHER ACFT WERE THE CONTRIBUTING FACTORS LEADING TO THIS.

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.