Flight crew of an medium large transport descended below assigned altitude due to a misunderstanding between crew members regarding the actual altitude to which cleared.

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Attributes
ACN	386840
Time
Date	199711
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : rbv airport : ewr
State Reference	NJ
Altitude	msl bound lower : 10400 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : n90
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
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 : first officer
Qualification	other other : other pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 240 flight time total : 6800 flight time type : 3040
ASRS Report	386840
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : crossing restriction not met altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Given crossing restr at holey intersection. Autoplt on. When aircraft did not level at the expected 11000 ft, leveled the aircraft manually at 11000 ft only to see altitude window set to 10000 ft. Captain and myself were unsure of correct altitude but unable to ask ATC because of radio congestion. Captain was convinced of the 10000 ft altitude. So I began descent. ATC confirmed 11000 ft as correct, but then cleared us to 10000 ft. Descent had been made to 10400 ft when ATC advised of error. Initially began immediate climb, but ATC cleared us to 10000 ft.

Original NASA ASRS Text

Title: FLC OF AN MLG DSNDED BELOW ASSIGNED ALT DUE TO A MISUNDERSTANDING BTWN CREW MEMBERS REGARDING THE ACTUAL ALT TO WHICH CLRED.

Narrative: GIVEN XING RESTR AT HOLEY INTXN. AUTOPLT ON. WHEN ACFT DID NOT LEVEL AT THE EXPECTED 11000 FT, LEVELED THE ACFT MANUALLY AT 11000 FT ONLY TO SEE ALT WINDOW SET TO 10000 FT. CAPT AND MYSELF WERE UNSURE OF CORRECT ALT BUT UNABLE TO ASK ATC BECAUSE OF RADIO CONGESTION. CAPT WAS CONVINCED OF THE 10000 FT ALT. SO I BEGAN DSCNT. ATC CONFIRMED 11000 FT AS CORRECT, BUT THEN CLRED US TO 10000 FT. DSCNT HAD BEEN MADE TO 10400 FT WHEN ATC ADVISED OF ERROR. INITIALLY BEGAN IMMEDIATE CLB, BUT ATC CLRED US TO 10000 FT.

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.