An air carrier twin engine widebody transport flight crew descended below their assigned altitude when they misunderstood the clearance in foreign airspace.

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Attributes
ACN	432864
Time
Date	199903
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : lmg.vortac
State Reference	FO
Altitude	msl bound lower : 33000 msl bound upper : 35000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : lfmm.artcc
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	other other vortac
Flight Phase	cruise : enroute altitude change
Route In Use	enroute airway : ns.airway
Flight Plan	IFR
Aircraft 2
Controlling Facilities	artcc : lfmm.artcc
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer pilot : cfi
ASRS Report	432864
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 120 flight time total : 20500 flight time type : 120
ASRS Report	432524
Events
Anomaly	altitude deviation : overshoot non adherence : clearance non adherence : far other anomaly other
Independent Detector	other controllera
Resolutory Action	controller : issued alert flight crew : returned to original clearance
Miss Distance	horizontal : 30000 vertical : 1000
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

While in cruise at FL390, we received clearance to descend to FL250 to be level in 5 mins. I, the first officer, read back the clearance to the controller. Approaching FL330, the controller asked our altitude. He then stated that we were only cleared to FL350. I told him that I read back clearance to FL250. The controller said to climb to FL350 and turn right 20 degrees. We started the climb to FL350 and made the right turn 20 degrees when we received a TCASII message, 'maintain vertical speed.' proximity to the aircraft appeared to be approximately 5-6 mi by a visual sighting and also on the TCASII display. We proceeded to our destination without further incident. Obviously there was a communication problem or perhaps a controller error. We heard FL250 and read back FL250 without a comment from the controller. Maybe it is the old problem of an american speaking to a french man in english after a long day.

Original NASA ASRS Text

Title: AN ACR TWIN ENG WDB FLC DSNDED BELOW THEIR ASSIGNED ALT WHEN THEY MISUNDERSTOOD THE CLRNC IN FOREIGN AIRSPACE.

Narrative: WHILE IN CRUISE AT FL390, WE RECEIVED CLRNC TO DSND TO FL250 TO BE LEVEL IN 5 MINS. I, THE FO, READ BACK THE CLRNC TO THE CTLR. APCHING FL330, THE CTLR ASKED OUR ALT. HE THEN STATED THAT WE WERE ONLY CLRED TO FL350. I TOLD HIM THAT I READ BACK CLRNC TO FL250. THE CTLR SAID TO CLB TO FL350 AND TURN R 20 DEGS. WE STARTED THE CLB TO FL350 AND MADE THE R TURN 20 DEGS WHEN WE RECEIVED A TCASII MESSAGE, 'MAINTAIN VERT SPD.' PROX TO THE ACFT APPEARED TO BE APPROX 5-6 MI BY A VISUAL SIGHTING AND ALSO ON THE TCASII DISPLAY. WE PROCEEDED TO OUR DEST WITHOUT FURTHER INCIDENT. OBVIOUSLY THERE WAS A COM PROB OR PERHAPS A CTLR ERROR. WE HEARD FL250 AND READ BACK FL250 WITHOUT A COMMENT FROM THE CTLR. MAYBE IT IS THE OLD PROB OF AN AMERICAN SPEAKING TO A FRENCH MAN IN ENGLISH AFTER A LONG DAY.

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.