Altitude deviation. Misunderstood clearance.

Attributes
ACN	313330
Time
Date	199508
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : bos
State Reference	MA
Altitude	msl bound lower : 5000 msl bound upper : 6000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : bos
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : approach descent other
Route In Use	arrival star : star
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : commercial pilot : instrument
Experience	flight time last 90 days : 240 flight time total : 9000 flight time type : 3000
ASRS Report	313330
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 30 flight time total : 12000
ASRS Report	313335
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were descending towards boston on the gardner 2 arrival approaching rever intersection. We had heard and acknowledged 5000 ft as the altitude assigned by ATC. Passing 6000 ft for 5000 ft, ATC told us to climb back to 6000 ft. ATC said 6000 ft was the assigned altitude. Either we heard it wrong or ATC gave us the incorrect altitude. We thought we heard 5000 ft. Most likely contributing factor was radio frequency congestion in the boston area affecting listening for instructions and confirming readbacks.

Original NASA ASRS Text

Title: ALTDEV. MISUNDERSTOOD CLRNC.

Narrative: WE WERE DSNDING TOWARDS BOSTON ON THE GARDNER 2 ARR APCHING REVER INTXN. WE HAD HEARD AND ACKNOWLEDGED 5000 FT AS THE ALT ASSIGNED BY ATC. PASSING 6000 FT FOR 5000 FT, ATC TOLD US TO CLB BACK TO 6000 FT. ATC SAID 6000 FT WAS THE ASSIGNED ALT. EITHER WE HEARD IT WRONG OR ATC GAVE US THE INCORRECT ALT. WE THOUGHT WE HEARD 5000 FT. MOST LIKELY CONTRIBUTING FACTOR WAS RADIO FREQ CONGESTION IN THE BOSTON AREA AFFECTING LISTENING FOR INSTRUCTIONS AND CONFIRMING READBACKS.

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.