Flight crew of a super MD80 overshot descent altitude due to a misunderstanding of the actual assign...

Attributes
ACN	365290
Time
Date	199704
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : bdf
State Reference	IL
Altitude	msl bound lower : 24000 msl bound upper : 25000
Environment
Light	Night
Aircraft 1
Controlling Facilities	artcc : zau
Operator	common carrier : air carrier
Make Model Name	MD-80 Super 80
Operating Under FAR Part	Part 121
Flight Phase	cruise other descent other
Flight Plan	IFR
Aircraft 2
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 : atp
ASRS Report	365290
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
ASRS Report	365289
Events
Anomaly	altitude deviation : overshoot conflict : airborne less severe non adherence : required legal separation 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
Miss Distance	horizontal : 16200 vertical : 600
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Approaching chicago, we were cleared to hold at bdf at FL250. Just as we started down, center called 'I need you down now.' I, the copilot, was flying. I was talking, responded 'we are starting down now.' center said, 'descend now to FL240.' I read that back and set it in the altitude window. My copilot verified it. As we leveled at FL240, we got an RA from TCASII and center told us to climb immediately to FL250. Center then said we had never been cleared below FL250. I later called the center, and was told that on the tape, my last readback, when I said roger descending to FL240, was stepped on, and the controller never heard that. They also said there was no clearance to FL240 that they remembered hearing on the tape as they reviewed it. I don't know how this happened -- both of us thought we read back a clearance correctly. I will request a transcript as soon as the office opens monday. Center says closest point of approach was 2.7 mi, 600 ft.

Original NASA ASRS Text

Title: FLC OF A SUPER MD80 OVERSHOT DSCNT ALT DUE TO A MISUNDERSTANDING OF THE ACTUAL ASSIGNED ALT.

Narrative: APCHING CHICAGO, WE WERE CLRED TO HOLD AT BDF AT FL250. JUST AS WE STARTED DOWN, CTR CALLED 'I NEED YOU DOWN NOW.' I, THE COPLT, WAS FLYING. I WAS TALKING, RESPONDED 'WE ARE STARTING DOWN NOW.' CTR SAID, 'DSND NOW TO FL240.' I READ THAT BACK AND SET IT IN THE ALT WINDOW. MY COPLT VERIFIED IT. AS WE LEVELED AT FL240, WE GOT AN RA FROM TCASII AND CTR TOLD US TO CLB IMMEDIATELY TO FL250. CTR THEN SAID WE HAD NEVER BEEN CLRED BELOW FL250. I LATER CALLED THE CTR, AND WAS TOLD THAT ON THE TAPE, MY LAST READBACK, WHEN I SAID ROGER DSNDING TO FL240, WAS STEPPED ON, AND THE CTLR NEVER HEARD THAT. THEY ALSO SAID THERE WAS NO CLRNC TO FL240 THAT THEY REMEMBERED HEARING ON THE TAPE AS THEY REVIEWED IT. I DON'T KNOW HOW THIS HAPPENED -- BOTH OF US THOUGHT WE READ BACK A CLRNC CORRECTLY. I WILL REQUEST A TRANSCRIPT AS SOON AS THE OFFICE OPENS MONDAY. CTR SAYS CLOSEST POINT OF APCH WAS 2.7 MI, 600 FT.

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.

Flight crew of a super MD80 overshot descent altitude due to a misunderstanding of the actual assigned altitude.