An air carrier MD88 flight crew descended below their assigned altitude.

Attributes
ACN	387857
Time
Date	199712
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : rmg
State Reference	GA
Altitude	msl bound lower : 31500 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : ztl tower : cur
Operator	common carrier : air carrier
Make Model Name	MD-88
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 240 flight time total : 9500 flight time type : 7200
ASRS Report	387857
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : commercial pilot : flight engineer pilot : atp pilot : cfi pilot : instrument
Experience	flight time last 90 days : 200 flight time total : 13000 flight time type : 3000
ASRS Report	387850
Events
Anomaly	altitude deviation : overshoot conflict : airborne less severe non adherence : far non adherence : clearance
Independent Detector	other controllera
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	faa : reviewed incident with flight crew Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

In cruise on a flight from ind to atl, flight attendant called and then was let into cockpit to offer drinks and discuss flight details. She entered and was talking to the captain when ATC (ZTL) issued a descent. I answered by saying we were descending to FL230. Passing FL317 controller told us to climb to FL330. We stopped descent at FL315 and commenced the climb. We received a TA from TCASII and the controller told us to quickly climb to FL330. We complied. Rptedly the controller had issued the descent for FL330. Contributing to this misunderstanding were the following factors: 1) my mishearing of the clearance due to the conversation in the cockpit (even though it was pertinent to the flight). 2) the captain not hearing the clearance. 3) the controller not catching the erroneous readback. Supplemental information from acn 387850: I was just finishing up listening to an updated ATIS when the cabin attendant gave the cockpit entry signal at the same time ATC gave us a clearance to descend and maintain FL230. The PF (first officer) set the altitude reminder and replied 'descending to FL230.' passing through FL317 ATC said 'climb and maintain FL330.' after level, the controller asked where we were descending to. I replied 'we were descending, cleared and read back FL230.' he replied, 'no, you were cleared to FL330.' when ATC listened to the tapes later, they said the controller clearly said FL330, but the first officer clearly read back FL230.

Original NASA ASRS Text

Title: AN ACR MD88 FLC DSNDED BELOW THEIR ASSIGNED ALT.

Narrative: IN CRUISE ON A FLT FROM IND TO ATL, FLT ATTENDANT CALLED AND THEN WAS LET INTO COCKPIT TO OFFER DRINKS AND DISCUSS FLT DETAILS. SHE ENTERED AND WAS TALKING TO THE CAPT WHEN ATC (ZTL) ISSUED A DSCNT. I ANSWERED BY SAYING WE WERE DSNDING TO FL230. PASSING FL317 CTLR TOLD US TO CLB TO FL330. WE STOPPED DSCNT AT FL315 AND COMMENCED THE CLB. WE RECEIVED A TA FROM TCASII AND THE CTLR TOLD US TO QUICKLY CLB TO FL330. WE COMPLIED. RPTEDLY THE CTLR HAD ISSUED THE DSCNT FOR FL330. CONTRIBUTING TO THIS MISUNDERSTANDING WERE THE FOLLOWING FACTORS: 1) MY MISHEARING OF THE CLRNC DUE TO THE CONVERSATION IN THE COCKPIT (EVEN THOUGH IT WAS PERTINENT TO THE FLT). 2) THE CAPT NOT HEARING THE CLRNC. 3) THE CTLR NOT CATCHING THE ERRONEOUS READBACK. SUPPLEMENTAL INFO FROM ACN 387850: I WAS JUST FINISHING UP LISTENING TO AN UPDATED ATIS WHEN THE CABIN ATTENDANT GAVE THE COCKPIT ENTRY SIGNAL AT THE SAME TIME ATC GAVE US A CLRNC TO DSND AND MAINTAIN FL230. THE PF (FO) SET THE ALT REMINDER AND REPLIED 'DSNDING TO FL230.' PASSING THROUGH FL317 ATC SAID 'CLB AND MAINTAIN FL330.' AFTER LEVEL, THE CTLR ASKED WHERE WE WERE DSNDING TO. I REPLIED 'WE WERE DSNDING, CLRED AND READ BACK FL230.' HE REPLIED, 'NO, YOU WERE CLRED TO FL330.' WHEN ATC LISTENED TO THE TAPES LATER, THEY SAID THE CTLR CLRLY SAID FL330, BUT THE FO CLRLY READ BACK FL230.

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.