Flight crew of an medium large transport overshot descent altitude due to ATC not hearing the incorrect readback altitude by the flight crew.

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Attributes
ACN	334720
Time
Date	199604
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : atl
State Reference	GA
Altitude	msl bound lower : 14500 msl bound upper : 16000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 133 flight time total : 12000 flight time type : 5000
ASRS Report	334720
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : overshoot conflict : ground critical non adherence : clearance non adherence : required legal separation other anomaly other
Independent Detector	other controllera
Resolutory Action	other
Consequence	faa : reviewed incident with flight crew Other
Miss Distance	horizontal : 15000 vertical : 500
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Operational Error Pilot Deviation

Narrative:

Captain was off ATC frequency talking with company. First officer took ATC clearance to descend to 13000 ft at 40 DME. At approximately 14500 ft ATC asked if we were at 16000 ft (the altitude ATC alleges we were cleared). On examining ATC tapes subsequent to event, it was discovered that our crew (first officer) did read back a descent to 13000 ft, which is the normal altitude for landing direction at the ATC 041 degree radial, 40 DME. We continued descent to 13000 ft and called 'center' on ground. ZTL indicated that the tape of the occurrence indicated our readback of 13000 ft which they indicated they did not catch. We joined the arrival as a fast mover (330 KTS) from the low altitude sector 22000 ft. Some difficulty might have occurred for the ATC controller as he was trying to work us into the arrival along with the high altitude arrs. They (ATC) indicated the loss of separation occurred with an inbound aircraft at 15000 ft. Had both pilots been on frequency, a backup for the alleged 16000 ft clearance with a subsequent 13000 ft readback might have been avoided. At no time did we receive a TCASII alert with the 15000 ft traffic.

Original NASA ASRS Text

Title: FLC OF AN MLG OVERSHOT DSCNT ALT DUE TO ATC NOT HEARING THE INCORRECT READBACK ALT BY THE FLC.

Narrative: CAPT WAS OFF ATC FREQ TALKING WITH COMPANY. FO TOOK ATC CLRNC TO DSND TO 13000 FT AT 40 DME. AT APPROX 14500 FT ATC ASKED IF WE WERE AT 16000 FT (THE ALT ATC ALLEGES WE WERE CLRED). ON EXAMINING ATC TAPES SUBSEQUENT TO EVENT, IT WAS DISCOVERED THAT OUR CREW (FO) DID READ BACK A DSCNT TO 13000 FT, WHICH IS THE NORMAL ALT FOR LNDG DIRECTION AT THE ATC 041 DEG RADIAL, 40 DME. WE CONTINUED DSCNT TO 13000 FT AND CALLED 'CTR' ON GND. ZTL INDICATED THAT THE TAPE OF THE OCCURRENCE INDICATED OUR READBACK OF 13000 FT WHICH THEY INDICATED THEY DID NOT CATCH. WE JOINED THE ARR AS A FAST MOVER (330 KTS) FROM THE LOW ALT SECTOR 22000 FT. SOME DIFFICULTY MIGHT HAVE OCCURRED FOR THE ATC CTLR AS HE WAS TRYING TO WORK US INTO THE ARR ALONG WITH THE HIGH ALT ARRS. THEY (ATC) INDICATED THE LOSS OF SEPARATION OCCURRED WITH AN INBOUND ACFT AT 15000 FT. HAD BOTH PLTS BEEN ON FREQ, A BACKUP FOR THE ALLEGED 16000 FT CLRNC WITH A SUBSEQUENT 13000 FT READBACK MIGHT HAVE BEEN AVOIDED. AT NO TIME DID WE RECEIVE A TCASII ALERT WITH THE 15000 FT TFC.

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.