B757 crew descended below the GS in canadian airspace.

Attributes
ACN	449078
Time
Date	199909
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : czyz.airport
State Reference	ON
Altitude	msl bound lower : 3600 msl bound upper : 4000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : cyyz.tracon tower : cyyz.tower
Operator	common carrier : air carrier
Make Model Name	B757-200
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 24r other
Flight Phase	descent : approach
Route In Use	approach : instrument precision arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	449078
Person 2
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
ASRS Report	449079
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued alert controller : issued new clearance
Supplementary
Problem Areas	Flight Crew Human Performance Company ATC Human Performance Airspace Structure
Primary Problem	Company
Air Traffic Incident	Pilot Deviation

Narrative:

Toronto approach instructed flight X to turn right to FL250 heading and intercept, descend on the GS. Previous altitude assigned was 4000 ft. During the intercept, aircraft was allowed to descend to 3600 ft MSL and the controller caught it and told flight X to maintain altitude until on the GS. Autoplt had been disconnected by PF. Different phraseology by canadian controllers, ie, descend on GS vice maintain 4000 ft until established may have contributed to this error. Supplemental information from acn 449079: at 4000 ft on a 210 degree heading to intercept localizer, ATC cleared us to descend on GS. Captain dialed in 2400 ft and began slow descent. I was doing flaps and checklist. I saw descent simultaneously with ATC call telling us to level at present altitude until GS intercept. We were at 3500 ft. There was no conflict and call to ATC said they had no problem. Confusion was due to difference between canada and united states clearance which would have been maintain 4000 ft until GS intercept.

Original NASA ASRS Text

Title: B757 CREW DSNDED BELOW THE GS IN CANADIAN AIRSPACE.

Narrative: TORONTO APCH INSTRUCTED FLT X TO TURN R TO FL250 HDG AND INTERCEPT, DSND ON THE GS. PREVIOUS ALT ASSIGNED WAS 4000 FT. DURING THE INTERCEPT, ACFT WAS ALLOWED TO DSND TO 3600 FT MSL AND THE CTLR CAUGHT IT AND TOLD FLT X TO MAINTAIN ALT UNTIL ON THE GS. AUTOPLT HAD BEEN DISCONNECTED BY PF. DIFFERENT PHRASEOLOGY BY CANADIAN CTLRS, IE, DSND ON GS VICE MAINTAIN 4000 FT UNTIL ESTABLISHED MAY HAVE CONTRIBUTED TO THIS ERROR. SUPPLEMENTAL INFO FROM ACN 449079: AT 4000 FT ON A 210 DEG HDG TO INTERCEPT LOC, ATC CLRED US TO DSND ON GS. CAPT DIALED IN 2400 FT AND BEGAN SLOW DSCNT. I WAS DOING FLAPS AND CHKLIST. I SAW DSCNT SIMULTANEOUSLY WITH ATC CALL TELLING US TO LEVEL AT PRESENT ALT UNTIL GS INTERCEPT. WE WERE AT 3500 FT. THERE WAS NO CONFLICT AND CALL TO ATC SAID THEY HAD NO PROB. CONFUSION WAS DUE TO DIFFERENCE BTWN CANADA AND UNITED STATES CLRNC WHICH WOULD HAVE BEEN MAINTAIN 4000 FT UNTIL GS INTERCEPT.

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.