Setting 29 point 98 inches instead of 998 millibars results in descent 350 ft below cleared altitude...

Attributes
ACN	565879
Time
Date	200211
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : ebbr.tracon airport : ebbr.airport
State Reference	FO
Altitude	msl single value : 2000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ebbu.tracon tower : mia.tower
Operator	common carrier : air carrier
Make Model Name	B767 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : relief pilot
Qualification	pilot : atp
ASRS Report	565879
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	565880
Events
Anomaly	altitude deviation : overshoot non adherence : company policies non adherence : published procedure other anomaly other other spatial deviation
Independent Detector	other controllerb
Resolutory Action	controller : issued advisory flight crew : returned to assigned altitude none taken : detected after the fact
Consequence	other
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

Our flight was cleared to 2000 ft with an altimeter of 998. The captain and first officer both mistakenly set 29.98 inches instead of 998 millibars. I was the relief pilot and didn't catch the error. As we descended to 2000 ft, we actually went a little lower due to the incorrect altimeter setting. ATC advised us to maintain 2000 ft. This clued us in to the mistaken altimeter setting. The captain and first officer set 998 millibars and saw that we were now below 2000 ft. We made an immediate correction back to 2000 ft. This is the classic altimeter error that we are taught to be aware of. Supplemental information from acn 565880: we were over 350 ft low when approach queried us as to our altitude. This event occurred on a WX divert after flying all night. I, the captain, had not flown to europe since apr/xx/02 and it had been 4 yrs since my last european trip prior to this trip. It was the classic 998 versus 29.98 error. I felt that this event was critical and should be added to the long list of altimeter setting errors. This could have been a much more serious/fatal error in a different scenario. Contributing to this was the fact that we had diverted to bru and we were all fatigued after the long flight coupled with holding at london -- followed by a divert to bru.

Original NASA ASRS Text

Title: SETTING 29 POINT 98 INCHES INSTEAD OF 998 MILLIBARS RESULTS IN DSCNT 350 FT BELOW CLRED ALT AND BELOW THE MSA DEPICTED ON THE ARPT APCH CHARTS AT BRUSSELS.

Narrative: OUR FLT WAS CLRED TO 2000 FT WITH AN ALTIMETER OF 998. THE CAPT AND FO BOTH MISTAKENLY SET 29.98 INCHES INSTEAD OF 998 MILLIBARS. I WAS THE RELIEF PLT AND DIDN'T CATCH THE ERROR. AS WE DSNDED TO 2000 FT, WE ACTUALLY WENT A LITTLE LOWER DUE TO THE INCORRECT ALTIMETER SETTING. ATC ADVISED US TO MAINTAIN 2000 FT. THIS CLUED US IN TO THE MISTAKEN ALTIMETER SETTING. THE CAPT AND FO SET 998 MILLIBARS AND SAW THAT WE WERE NOW BELOW 2000 FT. WE MADE AN IMMEDIATE CORRECTION BACK TO 2000 FT. THIS IS THE CLASSIC ALTIMETER ERROR THAT WE ARE TAUGHT TO BE AWARE OF. SUPPLEMENTAL INFO FROM ACN 565880: WE WERE OVER 350 FT LOW WHEN APCH QUERIED US AS TO OUR ALT. THIS EVENT OCCURRED ON A WX DIVERT AFTER FLYING ALL NIGHT. I, THE CAPT, HAD NOT FLOWN TO EUROPE SINCE APR/XX/02 AND IT HAD BEEN 4 YRS SINCE MY LAST EUROPEAN TRIP PRIOR TO THIS TRIP. IT WAS THE CLASSIC 998 VERSUS 29.98 ERROR. I FELT THAT THIS EVENT WAS CRITICAL AND SHOULD BE ADDED TO THE LONG LIST OF ALTIMETER SETTING ERRORS. THIS COULD HAVE BEEN A MUCH MORE SERIOUS/FATAL ERROR IN A DIFFERENT SCENARIO. CONTRIBUTING TO THIS WAS THE FACT THAT WE HAD DIVERTED TO BRU AND WE WERE ALL FATIGUED AFTER THE LONG FLT COUPLED WITH HOLDING AT LONDON -- FOLLOWED BY A DIVERT TO BRU.

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.

Setting 29 point 98 inches instead of 998 millibars results in descent 350 ft below cleared altitude and below the MSA depicted on the airport approach charts at brussels.