Air carrier crew misinterprets traffic call altitude for descent altitude.

Attributes
ACN	175866
Time
Date	199104
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : sjc
State Reference	CA
Altitude	msl bound lower : 6600 msl bound upper : 7000
Environment
Flight Conditions	VMC
Light	Dusk
Aircraft 1
Controlling Facilities	tower : mco
Operator	common carrier : air carrier
Make Model Name	Light Transport, Low Wing, 2 Turboprop Eng
Flight Phase	descent : approach
Route In Use	enroute airway : zoa
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 2700 flight time type : 900
ASRS Report	175866
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 240 flight time total : 3700 flight time type : 1000
ASRS Report	175862
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera
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	Pilot Deviation

Narrative:

We were being stepped down from our cruise altitude. We were just cleared to 7000' followed by a traffic update of 9 O'clock 4 mi 6000'. There was extreme congestion on the approach frequency and many calls were bring stepped on. The extreme congestion caused both crew men to misinterp the call to be a further descent to 6000'. As I tried to read back the clearance I believe I may have been stepped on. Another factor was that I had previously called the traffic in sight, this may have also been stepped on. Much of the time the radio was all squeals. ATC called to ask our altitude, which was 6500' and the problem was resolved. At no time was the traffic a conflict and safety was not compromised. I feel the problem would not have occurred had other aircraft used proper etiquette on the radio. By listening a few seconds before speaking the problem of stepping on other xmissions can be greatly reduced. This is especially important during very high workload portions of flight such as approach. Both the captain and myself understood the clearance to be a descent to 6000', if there had been a doubt we would have reverified the clearance. We were both rested and on the third leg of a 4 leg day.

Original NASA ASRS Text

Title: ACR CREW MISINTERPRETS TRAFFIC CALL ALT FOR DESCENT ALT.

Narrative: WE WERE BEING STEPPED DOWN FROM OUR CRUISE ALT. WE WERE JUST CLRED TO 7000' FOLLOWED BY A TFC UPDATE OF 9 O'CLOCK 4 MI 6000'. THERE WAS EXTREME CONGESTION ON THE APCH FREQ AND MANY CALLS WERE BRING STEPPED ON. THE EXTREME CONGESTION CAUSED BOTH CREW MEN TO MISINTERP THE CALL TO BE A FURTHER DSNT TO 6000'. AS I TRIED TO READ BACK THE CLRNC I BELIEVE I MAY HAVE BEEN STEPPED ON. ANOTHER FACTOR WAS THAT I HAD PREVIOUSLY CALLED THE TFC IN SIGHT, THIS MAY HAVE ALSO BEEN STEPPED ON. MUCH OF THE TIME THE RADIO WAS ALL SQUEALS. ATC CALLED TO ASK OUR ALT, WHICH WAS 6500' AND THE PROB WAS RESOLVED. AT NO TIME WAS THE TFC A CONFLICT AND SAFETY WAS NOT COMPROMISED. I FEEL THE PROB WOULD NOT HAVE OCCURRED HAD OTHER ACFT USED PROPER ETIQUETTE ON THE RADIO. BY LISTENING A FEW SECS BEFORE SPEAKING THE PROB OF STEPPING ON OTHER XMISSIONS CAN BE GREATLY REDUCED. THIS IS ESPECIALLY IMPORTANT DURING VERY HIGH WORKLOAD PORTIONS OF FLT SUCH AS APCH. BOTH THE CAPT AND MYSELF UNDERSTOOD THE CLRNC TO BE A DSNT TO 6000', IF THERE HAD BEEN A DOUBT WE WOULD HAVE REVERIFIED THE CLRNC. WE WERE BOTH RESTED AND ON THE THIRD LEG OF A 4 LEG DAY.

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.