Altitude deviation. Intercepting localizer above GS descended prematurely.

Attributes
ACN	309510
Time
Date	199507
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : dtw
State Reference	MI
Altitude	msl bound lower : 4700 msl bound upper : 5000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dtw
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : approach descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 15000 flight time type : 7500
ASRS Report	309510
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : far non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were given a turn from downwind to crosswind and descend from 7000 ft to 5000 ft, then were instructed to intercept runway 21L localizer. During this process approach control was extremely busy and I thought we were also cleared for the approach. However the copilot and I realized after I descended through 5000 ft to 4700 ft that we were only cleared to intercept the localizer. Also I was above the GS at 5000 ft, and logically it made sense to intercept the GS also. I climbed back to 5000 ft and almost simultaneously was given approach clearance, and proceeded out of 5000 ft to capture GS. As always, dtw approach control was extremely busy, at times so busy you don't have time to respond to instructions before the controller is giving instructions to another aircraft, which causes confusion especially when you can't read back the instructions or question them. Less aircraft working with a controller, possibly make a double final controller say at 15-25 mi, then one at 8-15 mi to reduce the number of aircraft on a particular frequency.

Original NASA ASRS Text

Title: ALTDEV. INTERCEPTING LOC ABOVE GS DSNDED PREMATURELY.

Narrative: WE WERE GIVEN A TURN FROM DOWNWIND TO XWIND AND DSND FROM 7000 FT TO 5000 FT, THEN WERE INSTRUCTED TO INTERCEPT RWY 21L LOC. DURING THIS PROCESS APCH CTL WAS EXTREMELY BUSY AND I THOUGHT WE WERE ALSO CLRED FOR THE APCH. HOWEVER THE COPLT AND I REALIZED AFTER I DSNDED THROUGH 5000 FT TO 4700 FT THAT WE WERE ONLY CLRED TO INTERCEPT THE LOC. ALSO I WAS ABOVE THE GS AT 5000 FT, AND LOGICALLY IT MADE SENSE TO INTERCEPT THE GS ALSO. I CLBED BACK TO 5000 FT AND ALMOST SIMULTANEOUSLY WAS GIVEN APCH CLRNC, AND PROCEEDED OUT OF 5000 FT TO CAPTURE GS. AS ALWAYS, DTW APCH CTL WAS EXTREMELY BUSY, AT TIMES SO BUSY YOU DON'T HAVE TIME TO RESPOND TO INSTRUCTIONS BEFORE THE CTLR IS GIVING INSTRUCTIONS TO ANOTHER ACFT, WHICH CAUSES CONFUSION ESPECIALLY WHEN YOU CAN'T READ BACK THE INSTRUCTIONS OR QUESTION THEM. LESS ACFT WORKING WITH A CTLR, POSSIBLY MAKE A DOUBLE FINAL CTLR SAY AT 15-25 MI, THEN ONE AT 8-15 MI TO REDUCE THE NUMBER OF ACFT ON A PARTICULAR FREQ.

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.