A B737-200 flight crew descended below the assigned altitude near hcm VOR and received a TCASII TA.

Attributes
ACN	452365
Time
Date	199910
Day	Wed
Local Time Of Day	1201 To 1800
Place
State Reference	VA
Altitude	msl bound lower : 12500 msl bound upper : 14000
Environment
Flight Conditions	IMC
Weather Elements	Rain Turbulence
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zdc.artcc
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Flight Phase	descent : vacating altitude
Route In Use	arrival star : terks 2
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : zdc.artcc
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp pilot : commercial
Experience	flight time last 90 days : 200 flight time total : 13300 flight time type : 1600
ASRS Report	452365
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : flight engineer pilot : commercial
Experience	flight time last 90 days : 200 flight time total : 8000 flight time type : 3000
ASRS Report	452385
Events
Anomaly	altitude deviation : excursion from assigned altitude conflict : airborne less severe non adherence : clearance non adherence : published procedure non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	flight crew : returned to assigned altitude
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	ATC Human Performance

Narrative:

While descending on the terks 2 arrival to orf in heavy rain with continued light turbulence, we accepted a clearance to cross harcum at 10000 ft. The controller had a heavy workload and turbulence below FL310 had numerous aircraft asking about ride information and requests for lower altitudes. We first were called by a transposed call sign. After questioning the controller, we read back, 'cross harcum at 10000 ft.' both pilots pointed to the mode control altitude of 10000 ft as per company procedure. I was the PF and started a gradual descent of approximately 1200 FPM. At about 13000 ft, got a TA on TCASII. Shortly thereafter, we were asked by the controller to 'say your altitude.' we responded, and were told that we had not been given lower than 14000 ft and to climb back to 14000 ft. This was not a good feeling. We climbed up to 14000 ft and stated that we had in fact been given lower and had read that clearance back. I am convinced that we read back 10000 ft and very sure that we were given 10000 ft. Initially calling us by the wrong call sign was probably a factor. ZDC was very busy. The controller admitted that he hadn't in fact heard our readback. When asked if there had been a conflict, he replied that he had taken care of it.

Original NASA ASRS Text

Title: A B737-200 FLC DSNDED BELOW THE ASSIGNED ALT NEAR HCM VOR AND RECEIVED A TCASII TA.

Narrative: WHILE DSNDING ON THE TERKS 2 ARR TO ORF IN HVY RAIN WITH CONTINUED LIGHT TURB, WE ACCEPTED A CLRNC TO CROSS HARCUM AT 10000 FT. THE CTLR HAD A HVY WORKLOAD AND TURB BELOW FL310 HAD NUMEROUS ACFT ASKING ABOUT RIDE INFO AND REQUESTS FOR LOWER ALTS. WE FIRST WERE CALLED BY A TRANSPOSED CALL SIGN. AFTER QUESTIONING THE CTLR, WE READ BACK, 'CROSS HARCUM AT 10000 FT.' BOTH PLTS POINTED TO THE MODE CTL ALT OF 10000 FT AS PER COMPANY PROC. I WAS THE PF AND STARTED A GRADUAL DSCNT OF APPROX 1200 FPM. AT ABOUT 13000 FT, GOT A TA ON TCASII. SHORTLY THEREAFTER, WE WERE ASKED BY THE CTLR TO 'SAY YOUR ALT.' WE RESPONDED, AND WERE TOLD THAT WE HAD NOT BEEN GIVEN LOWER THAN 14000 FT AND TO CLB BACK TO 14000 FT. THIS WAS NOT A GOOD FEELING. WE CLBED UP TO 14000 FT AND STATED THAT WE HAD IN FACT BEEN GIVEN LOWER AND HAD READ THAT CLRNC BACK. I AM CONVINCED THAT WE READ BACK 10000 FT AND VERY SURE THAT WE WERE GIVEN 10000 FT. INITIALLY CALLING US BY THE WRONG CALL SIGN WAS PROBABLY A FACTOR. ZDC WAS VERY BUSY. THE CTLR ADMITTED THAT HE HADN'T IN FACT HEARD OUR READBACK. WHEN ASKED IF THERE HAD BEEN A CONFLICT, HE REPLIED THAT HE HAD TAKEN CARE OF IT.

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.