B737-800 has an altitude deviation during descent on the KORRY3 to lga.

Attributes
ACN	699948
Time
Date	200606
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : zny.artcc
State Reference	NY
Altitude	msl single value : 11000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zny.artcc
Operator	common carrier : air carrier
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	699948
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : overrode automation flight crew : returned to assigned altitude flight crew : overcame equipment problem
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

Descending on eno.KORRY3 into lga. Descending in VNAV speed mode and 10000 ft set in MCP altitude window; airplane descending below 11000 ft hard altitude on legs page and on VNAV descent page 2.3 mi before brand to about 10400 ft before captain disconnected autoplt and returned to 11000 ft. Also went to level change but 10000 ft already acquired. ATC said nothing and korry was crossed at 10000 ft. VNAV speed descent is supposed to honor altitude restrs but it didn't for brand. I use both path and descent modes all the time and have never seen this happen. This was blatant and the airplane didn't try to level before brand at all. Software maybe. Again both pages legs 11000 ft at brand and VNAV descent page 11000 ft were magenta and we were on both pages just like we were supposed to be.

Original NASA ASRS Text

Title: B737-800 HAS AN ALTDEV DURING DSCNT ON THE KORRY3 TO LGA.

Narrative: DSNDING ON ENO.KORRY3 INTO LGA. DSNDING IN VNAV SPD MODE AND 10000 FT SET IN MCP ALT WINDOW; AIRPLANE DSNDING BELOW 11000 FT HARD ALT ON LEGS PAGE AND ON VNAV DSCNT PAGE 2.3 MI BEFORE BRAND TO ABOUT 10400 FT BEFORE CAPT DISCONNECTED AUTOPLT AND RETURNED TO 11000 FT. ALSO WENT TO LEVEL CHANGE BUT 10000 FT ALREADY ACQUIRED. ATC SAID NOTHING AND KORRY WAS CROSSED AT 10000 FT. VNAV SPD DSCNT IS SUPPOSED TO HONOR ALT RESTRS BUT IT DIDN'T FOR BRAND. I USE BOTH PATH AND DSCNT MODES ALL THE TIME AND HAVE NEVER SEEN THIS HAPPEN. THIS WAS BLATANT AND THE AIRPLANE DIDN'T TRY TO LEVEL BEFORE BRAND AT ALL. SOFTWARE MAYBE. AGAIN BOTH PAGES LEGS 11000 FT AT BRAND AND VNAV DSCNT PAGE 11000 FT WERE MAGENTA AND WE WERE ON BOTH PAGES JUST LIKE WE WERE SUPPOSED TO BE.

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.