N90 issues MSAW alert to GLF4 flight crew due to early descent on GPS runway 4 approach.

Attributes
ACN	514451
Time
Date	200106
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	intersection : matty
State Reference	NY
Altitude	msl bound lower : 1200 msl bound upper : 1500
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : fok.tower
Operator	general aviation : corporate
Make Model Name	Gulfstream IV
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	arrival star : gps 24
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 130 flight time total : 13500 flight time type : 2800
ASRS Report	514451
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Events
Anomaly	altitude deviation : crossing restriction not met non adherence : clearance non adherence : published procedure other spatial deviation
Independent Detector	atc equipment : msaw atc equipment other atc equipment : radar
Resolutory Action	controller : issued alert flight crew : returned to original clearance
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

I was flying the GPS 24 at fok, which requires an altitude of 1500 ft MSL until the FAF, and then descend to MDA. After passing 'matty' (not the FAF), I started a slow descent. The copilot pointed out that we had not yet reached the FAF and I immediately started a climb back to 1500 ft. The tower (or approach) called with a low altitude alert. I estimate the aircraft went as low as 1200 ft before correcting back. The approach was over water and flat, sea level terrain, and I may not have been as concerned with altitude adherence as I normally am.

Original NASA ASRS Text

Title: N90 ISSUES MSAW ALERT TO GLF4 FLC DUE TO EARLY DSCNT ON GPS RWY 4 APCH.

Narrative: I WAS FLYING THE GPS 24 AT FOK, WHICH REQUIRES AN ALT OF 1500 FT MSL UNTIL THE FAF, AND THEN DSND TO MDA. AFTER PASSING 'MATTY' (NOT THE FAF), I STARTED A SLOW DSCNT. THE COPLT POINTED OUT THAT WE HAD NOT YET REACHED THE FAF AND I IMMEDIATELY STARTED A CLB BACK TO 1500 FT. THE TWR (OR APCH) CALLED WITH A LOW ALT ALERT. I ESTIMATE THE ACFT WENT AS LOW AS 1200 FT BEFORE CORRECTING BACK. THE APCH WAS OVER WATER AND FLAT, SEA LEVEL TERRAIN, AND I MAY NOT HAVE BEEN AS CONCERNED WITH ALT ADHERENCE AS I NORMALLY AM.

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.