Narrative:

We had descended to 11000' approximately 35 mi northeast of den, and were a heading of 180 degrees assigned by ATC (frequency 120.2). The captain was communicating with company when we were handed off to frequency 125.3. I dialed in the new frequency, then the captain said he was back up on ATC frequency. He checked in with the new controller. I then heard company (at the time I thought I heard ieg) 'heading 180 degrees, expect 26R, maintain 8000'.' the captain responded to this call, though I'm not sure of his exact wording. I thought it was earlier than normal for this descent, but started down anyway. At approximately 10600' the controller said company ieg climb immediately to 11000'. I pulled up and added power and was at 11000' within 3 or 4 seconds. At this point I expected him to call traffic, but instead he asked us to verify assigned altitude. We replied 11000' (since that was what he had just given us). We then told him that we had been cleared to 8000', he replied that the call had been for another company aircraft, and to listen more closely since there were several company flts on that frequency. No other aircraft were involved, and no evasive action was required. We continued to den west/O incident. 3 causes (or possible causes) come to mind: controller error (either in call sign or assigned altitude); instructions I heard were for another aircraft and I mistook the captain's communication with company for a readback to ATC; or company flts geg and ieb were both on frequency, we replied simultaneously to their instructions and, due to their proximity to the radio facility, our response was covered. Other factors: distrs caused by monitoring both company and ATC frequencys at same time. Noise level (from airflow) inside this particular aircraft is louder than most in company fleet. Several (3-5) company aircraft on same frequency. Fatigue. It was the last day of a 4 day trip. All days outside temperatures were sub zero. Airflow in cockpits was less than sufficient to make for a comfortable environment west/O coat and gloves (it was cold enough that our feet sometimes got numb in flight). In fact, we had commented on how tired we were getting and were glad to be on the last day. Things that could prevent recurrence: sterile cockpit and no unnecessary company communications not only below 10000', but also within 50 mi of an airport within a TCA or arsa. Working altitude alert system. Captain had not reset altitude (indicating cause #2 very likely), therefore alert would have caused further inquiry on our part. Pilots and controllers--listen up.

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Original NASA ASRS Text

Title: ACR MDT ALT DEVIATION EXCURSION FROM CLRNC ALT IN RESPONSE TO WRONG CALL SIGN.

Narrative: WE HAD DSNDED TO 11000' APPROX 35 MI NE OF DEN, AND WERE A HDG OF 180 DEGS ASSIGNED BY ATC (FREQ 120.2). THE CAPT WAS COMMUNICATING WITH COMPANY WHEN WE WERE HANDED OFF TO FREQ 125.3. I DIALED IN THE NEW FREQ, THEN THE CAPT SAID HE WAS BACK UP ON ATC FREQ. HE CHKED IN WITH THE NEW CTLR. I THEN HEARD COMPANY (AT THE TIME I THOUGHT I HEARD IEG) 'HDG 180 DEGS, EXPECT 26R, MAINTAIN 8000'.' THE CAPT RESPONDED TO THIS CALL, THOUGH I'M NOT SURE OF HIS EXACT WORDING. I THOUGHT IT WAS EARLIER THAN NORMAL FOR THIS DSCNT, BUT STARTED DOWN ANYWAY. AT APPROX 10600' THE CTLR SAID COMPANY IEG CLB IMMEDIATELY TO 11000'. I PULLED UP AND ADDED PWR AND WAS AT 11000' WITHIN 3 OR 4 SECS. AT THIS POINT I EXPECTED HIM TO CALL TFC, BUT INSTEAD HE ASKED US TO VERIFY ASSIGNED ALT. WE REPLIED 11000' (SINCE THAT WAS WHAT HE HAD JUST GIVEN US). WE THEN TOLD HIM THAT WE HAD BEEN CLRED TO 8000', HE REPLIED THAT THE CALL HAD BEEN FOR ANOTHER COMPANY ACFT, AND TO LISTEN MORE CLOSELY SINCE THERE WERE SEVERAL COMPANY FLTS ON THAT FREQ. NO OTHER ACFT WERE INVOLVED, AND NO EVASIVE ACTION WAS REQUIRED. WE CONTINUED TO DEN W/O INCIDENT. 3 CAUSES (OR POSSIBLE CAUSES) COME TO MIND: CTLR ERROR (EITHER IN CALL SIGN OR ASSIGNED ALT); INSTRUCTIONS I HEARD WERE FOR ANOTHER ACFT AND I MISTOOK THE CAPT'S COM WITH COMPANY FOR A READBACK TO ATC; OR COMPANY FLTS GEG AND IEB WERE BOTH ON FREQ, WE REPLIED SIMULTANEOUSLY TO THEIR INSTRUCTIONS AND, DUE TO THEIR PROX TO THE RADIO FAC, OUR RESPONSE WAS COVERED. OTHER FACTORS: DISTRS CAUSED BY MONITORING BOTH COMPANY AND ATC FREQS AT SAME TIME. NOISE LEVEL (FROM AIRFLOW) INSIDE THIS PARTICULAR ACFT IS LOUDER THAN MOST IN COMPANY FLEET. SEVERAL (3-5) COMPANY ACFT ON SAME FREQ. FATIGUE. IT WAS THE LAST DAY OF A 4 DAY TRIP. ALL DAYS OUTSIDE TEMPS WERE SUB ZERO. AIRFLOW IN COCKPITS WAS LESS THAN SUFFICIENT TO MAKE FOR A COMFORTABLE ENVIRONMENT W/O COAT AND GLOVES (IT WAS COLD ENOUGH THAT OUR FEET SOMETIMES GOT NUMB IN FLT). IN FACT, WE HAD COMMENTED ON HOW TIRED WE WERE GETTING AND WERE GLAD TO BE ON THE LAST DAY. THINGS THAT COULD PREVENT RECURRENCE: STERILE COCKPIT AND NO UNNECESSARY COMPANY COMS NOT ONLY BELOW 10000', BUT ALSO WITHIN 50 MI OF AN ARPT WITHIN A TCA OR ARSA. WORKING ALT ALERT SYS. CAPT HAD NOT RESET ALT (INDICATING CAUSE #2 VERY LIKELY), THEREFORE ALERT WOULD HAVE CAUSED FURTHER INQUIRY ON OUR PART. PLTS AND CTLRS--LISTEN UP.

Data retrieved from NASA's ASRS site as of August 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.