B767 descended below assigned altitude.

Attributes
ACN	344719
Time
Date	199608
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : lsa
State Reference	FO
Altitude	msl bound lower : 26500 msl bound upper : 27000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : lfmm
Operator	common carrier : air carrier
Make Model Name	B767 Undifferentiated or Other Model
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 : captain oversight : pic
Qualification	pilot : atp
ASRS Report	344719
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer other personnel other
Qualification	pilot : atp
ASRS Report	344730
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Clearance was given and read back to descend to FL200 by marseille control. At FL265, control queried altitude passing. We stated FL265 for FL200. They then reclred us to descend to FL250 stating the original descent clearance was FL270. Both ATC and flight crew misunderstood each other's pronunciation of numbers in clearance and readback. Traffic and terrain was not a factor.

Original NASA ASRS Text

Title: B767 DSNDED BELOW ASSIGNED ALT.

Narrative: CLRNC WAS GIVEN AND READ BACK TO DSND TO FL200 BY MARSEILLE CTL. AT FL265, CTL QUERIED ALT PASSING. WE STATED FL265 FOR FL200. THEY THEN RECLRED US TO DSND TO FL250 STATING THE ORIGINAL DSCNT CLRNC WAS FL270. BOTH ATC AND FLC MISUNDERSTOOD EACH OTHER'S PRONUNCIATION OF NUMBERS IN CLRNC AND READBACK. TFC AND TERRAIN WAS NOT A FACTOR.

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.