A B757 crew descended to MDA early at lga, causing an MSA warning to be issued by the tower.

Attributes
ACN	522596
Time
Date	200108
Day	Fri
Local Time Of Day	0001 To 0600
Place
Locale Reference	airport : lga.airport
State Reference	NY
Altitude	msl bound lower : 600 msl bound upper : 640
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tower : lga.tower tracon : sct.tracon
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 31 other
Flight Phase	descent : approach
Route In Use	approach : instrument precision
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 50 flight time total : 9000 flight time type : 6500
ASRS Report	522596
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : private pilot : atp pilot : instrument pilot : flight engineer pilot : commercial pilot : cfi pilot : multi engine
Experience	flight time last 90 days : 150 flight time total : 10000 flight time type : 400
ASRS Report	522743
Events
Anomaly	altitude deviation : overshoot altitude deviation : crossing restriction not met altitude deviation : excursion from assigned altitude non adherence : clearance non adherence : published procedure
Independent Detector	atc equipment : msaw other controllera
Resolutory Action	controller : issued alert
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Airport Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Localizer approach to runway 31 at lga. MDA of 600 ft with step-down fix of 640 ft at 2.7 DME. Descended to 600 ft early so we were 40 ft low at the 2.7 mi fix. Tower called out low altitude alert and check altimeters. We had a visual on the runway, local obstructions, and the correct altimeter setting. Rest of approach and landing uneventful. Supplemental information from acn 522743: descended directly to 600 ft MSL instead of 640 ft published. Reached 600 ft in VMC .3 mi before published descent point. Tower advised of low altitude alert and confirmed latest altimeter setting.

Original NASA ASRS Text

Title: A B757 CREW DSNDED TO MDA EARLY AT LGA, CAUSING AN MSA WARNING TO BE ISSUED BY THE TWR.

Narrative: LOC APCH TO RWY 31 AT LGA. MDA OF 600 FT WITH STEP-DOWN FIX OF 640 FT AT 2.7 DME. DSNDED TO 600 FT EARLY SO WE WERE 40 FT LOW AT THE 2.7 MI FIX. TWR CALLED OUT LOW ALT ALERT AND CHK ALTIMETERS. WE HAD A VISUAL ON THE RWY, LCL OBSTRUCTIONS, AND THE CORRECT ALTIMETER SETTING. REST OF APCH AND LNDG UNEVENTFUL. SUPPLEMENTAL INFO FROM ACN 522743: DSNDED DIRECTLY TO 600 FT MSL INSTEAD OF 640 FT PUBLISHED. REACHED 600 FT IN VMC .3 MI BEFORE PUBLISHED DSCNT POINT. TWR ADVISED OF LOW ALT ALERT AND CONFIRMED LATEST ALTIMETER SETTING.

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.