DC9 crew misinterped clearance and slowed to final approach speed early.

Attributes
ACN	498790
Time
Date	200101
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : dtw.airport
State Reference	MI
Altitude	msl single value : 4000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	tracon : d21.tracon
Operator	common carrier : air carrier
Make Model Name	DC-9 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 295
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 : 200 flight time total : 8000 flight time type : 2500
ASRS Report	498790
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : commercial pilot : instrument
Events
Anomaly	non adherence : clearance non adherence : published procedure other anomaly other
Independent Detector	other controllera
Resolutory Action	none taken : insufficient time
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Flight Crew Human Performance Weather ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Captain was PF. Cleared to maintain 5000 ft and 170 KTS to robbi intersection (13.9 DME) and cleared ILS runway 21L approach. At robbi intersection, aircraft configured to land and slowed to 133 KTS. At approximately 10 DME, dtw final control monitor queried us 'what speed are you doing anyway?' we replied '133 KTS.' his response was 'you were told 'to maintain 170 KTS until the marker.' we replied 'no, we were told until robbi.' he asked us to speed back up until the marker (4 NM). I replied 'unable.' I felt making a big change in speed and/or confign 4 mi from the marker and then changing back was unsafe due to the 2000 ft RVR conditions. I would have preferred a go around. Tracking down the GS 9 mi out in these conditions is no place to make big changes. He then instructed us to call him on the ground and gave us the phone number 'for a possible pilot deviation.' I don't believe this was the appropriate time to be telling us this. He should have waited until we were on the ground. When I called him, he told me we were wrong about the clearance and we were supposed to maintain 170 KTS to the marker. I told him why I was unable to speed up for 4 mi and that we certainly read back the clearance as we understood it. Incidentally, flying that fast to the FAF is significantly different from normal operating procedures.

Original NASA ASRS Text

Title: DC9 CREW MISINTERPED CLRNC AND SLOWED TO FINAL APCH SPD EARLY.

Narrative: CAPT WAS PF. CLRED TO MAINTAIN 5000 FT AND 170 KTS TO ROBBI INTXN (13.9 DME) AND CLRED ILS RWY 21L APCH. AT ROBBI INTXN, ACFT CONFIGURED TO LAND AND SLOWED TO 133 KTS. AT APPROX 10 DME, DTW FINAL CTL MONITOR QUERIED US 'WHAT SPD ARE YOU DOING ANYWAY?' WE REPLIED '133 KTS.' HIS RESPONSE WAS 'YOU WERE TOLD 'TO MAINTAIN 170 KTS UNTIL THE MARKER.' WE REPLIED 'NO, WE WERE TOLD UNTIL ROBBI.' HE ASKED US TO SPD BACK UP UNTIL THE MARKER (4 NM). I REPLIED 'UNABLE.' I FELT MAKING A BIG CHANGE IN SPD AND/OR CONFIGN 4 MI FROM THE MARKER AND THEN CHANGING BACK WAS UNSAFE DUE TO THE 2000 FT RVR CONDITIONS. I WOULD HAVE PREFERRED A GAR. TRACKING DOWN THE GS 9 MI OUT IN THESE CONDITIONS IS NO PLACE TO MAKE BIG CHANGES. HE THEN INSTRUCTED US TO CALL HIM ON THE GND AND GAVE US THE PHONE NUMBER 'FOR A POSSIBLE PLTDEV.' I DON'T BELIEVE THIS WAS THE APPROPRIATE TIME TO BE TELLING US THIS. HE SHOULD HAVE WAITED UNTIL WE WERE ON THE GND. WHEN I CALLED HIM, HE TOLD ME WE WERE WRONG ABOUT THE CLRNC AND WE WERE SUPPOSED TO MAINTAIN 170 KTS TO THE MARKER. I TOLD HIM WHY I WAS UNABLE TO SPD UP FOR 4 MI AND THAT WE CERTAINLY READ BACK THE CLRNC AS WE UNDERSTOOD IT. INCIDENTALLY, FLYING THAT FAST TO THE FAF IS SIGNIFICANTLY DIFFERENT FROM NORMAL OPERATING PROCS.

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.