<< >> NASA ASRS Report 678672, November 2005

B777 flight crew failed to reset altimeter soon enough to avoid overshooting 17000 ft clearance on descent with very low local pressure.

Attributes
ACN	678672
Time
Date	200511
Local Time Of Day	1801 To 2400
Place
Locale Reference	intersection : scupp
State Reference	MA
Altitude	msl bound lower : 17000 msl bound upper : 18000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zbw.artcc
Operator	common carrier : air carrier
Make Model Name	B777 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : approach descent : holding
Flight Plan	IFR
Person 1
Function	flight crew : captain oversight : pic
ASRS Report	678672
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	altitude deviation : overshoot altitude deviation : crossing restriction not met non adherence : clearance other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	none taken : detected after the fact
Supplementary
Problem Areas	Flight Crew Human Performance Weather
Primary Problem	Weather

Narrative:

Bos altimeter was low; 28.73; on the first ATIS we received prior to descending into boston; and then 28.85 on the next ATIS. We both commented on the low setting and the need to be vigilant in setting altimeters. Initially we had clearance to cross scupp at 11000 ft. This was revised to a descent to 13000 ft; and then again revised to a descent to 17000 ft. At approximately FL180 we were issued holding instructions for scupp intersection. I was copying the instructions as we neared FL180 and when changing the altimeters to qnh we realized we were already past 17000 ft due to the large pressure difference. ZBW gave us 15000 ft at the same time. After landing; both the first officer and I realized how easy it is to let a simple distraction (the holding instructions) interfere with good airmanship. This was particularly frustrating since we were aware well in advance of the low altimeter and the possible issues associated with it. In the future; with a very low altimeter setting; planning to switch to qnh well in advance of FL180 will prevent a possible altitude excursion.

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Original NASA ASRS Text

Title: B777 FLT CREW FAILED TO RESET ALTIMETER SOON ENOUGH TO AVOID OVERSHOOTING 17000 FT CLRNC ON DSCNT WITH VERY LOW LCL PRESSURE.

Narrative: BOS ALTIMETER WAS LOW; 28.73; ON THE FIRST ATIS WE RECEIVED PRIOR TO DSNDING INTO BOSTON; AND THEN 28.85 ON THE NEXT ATIS. WE BOTH COMMENTED ON THE LOW SETTING AND THE NEED TO BE VIGILANT IN SETTING ALTIMETERS. INITIALLY WE HAD CLRNC TO CROSS SCUPP AT 11000 FT. THIS WAS REVISED TO A DSCNT TO 13000 FT; AND THEN AGAIN REVISED TO A DSCNT TO 17000 FT. AT APPROX FL180 WE WERE ISSUED HOLDING INSTRUCTIONS FOR SCUPP INTXN. I WAS COPYING THE INSTRUCTIONS AS WE NEARED FL180 AND WHEN CHANGING THE ALTIMETERS TO QNH WE REALIZED WE WERE ALREADY PAST 17000 FT DUE TO THE LARGE PRESSURE DIFFERENCE. ZBW GAVE US 15000 FT AT THE SAME TIME. AFTER LNDG; BOTH THE FO AND I REALIZED HOW EASY IT IS TO LET A SIMPLE DISTR (THE HOLDING INSTRUCTIONS) INTERFERE WITH GOOD AIRMANSHIP. THIS WAS PARTICULARLY FRUSTRATING SINCE WE WERE AWARE WELL IN ADVANCE OF THE LOW ALTIMETER AND THE POSSIBLE ISSUES ASSOCIATED WITH IT. IN THE FUTURE; WITH A VERY LOW ALTIMETER SETTING; PLANNING TO SWITCH TO QNH WELL IN ADVANCE OF FL180 WILL PREVENT A POSSIBLE ALT EXCURSION.

Data retrieved from NASA's ASRS site as of January 2009 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.