Cleared descend to 11000', flight crew misunderstood and descended to 9000'.

Attributes
ACN	82801
Time
Date	198802
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dfw
State Reference	TX
Altitude	msl bound lower : 9000 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dfw tower : syr
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other 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 : 200 flight time total : 10000 flight time type : 8000
ASRS Report	82801
Person 2
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera
Resolutory Action	other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

After all of this time and experience, I'm very cognizant re attention to those items. On the flight we had new engineer trainers in progress with a check engineer, and at some time about this time a logbook item was brought up from the cabin. I heard the copilot read back 9000' descent to the controller and watched him set it in the altitude alert. To this day he swears he heard 9000'. I'm not going to swear on the bible, but thought that we did. In fact, we had a radio change and while still at higher altitude, read back the 9000' clearance altitude west/O any question. It was after leveling and flying at 9000' for I'm guessing a minute, that our altitude was questioned, that it should have been 11000' instead of 9000'.

Original NASA ASRS Text

Title: CLEARED DESCEND TO 11000', FLT CREW MISUNDERSTOOD AND DESCENDED TO 9000'.

Narrative: AFTER ALL OF THIS TIME AND EXPERIENCE, I'M VERY COGNIZANT RE ATTN TO THOSE ITEMS. ON THE FLT WE HAD NEW ENGINEER TRAINERS IN PROGRESS WITH A CHK ENGINEER, AND AT SOME TIME ABOUT THIS TIME A LOGBOOK ITEM WAS BROUGHT UP FROM THE CABIN. I HEARD THE COPLT READ BACK 9000' DSCNT TO THE CTLR AND WATCHED HIM SET IT IN THE ALT ALERT. TO THIS DAY HE SWEARS HE HEARD 9000'. I'M NOT GOING TO SWEAR ON THE BIBLE, BUT THOUGHT THAT WE DID. IN FACT, WE HAD A RADIO CHANGE AND WHILE STILL AT HIGHER ALT, READ BACK THE 9000' CLRNC ALT W/O ANY QUESTION. IT WAS AFTER LEVELING AND FLYING AT 9000' FOR I'M GUESSING A MINUTE, THAT OUR ALT WAS QUESTIONED, THAT IT SHOULD HAVE BEEN 11000' INSTEAD OF 9000'.

Data retrieved from NASA's ASRS site as of August 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.