Air carrier X descent to occupied altitude had less than standard separation from aircraft Y. System...

Attributes
ACN	227027
Time
Date	199211
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dxo
State Reference	MI
Altitude	msl bound lower : 7000 msl bound upper : 7000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : dtw
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Aircraft 2
Operator	general aviation : personal
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : approach
Qualification	controller : radar
Experience	controller non radar : 3 controller radar : 4
ASRS Report	227027
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe non adherence : published procedure non adherence : required legal separation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	faa : investigated
Miss Distance	horizontal : 14400 vertical : 700
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

2 aircraft arriving dtw, base leg traffic descending to 7000 according to SOP. Downwind air carrier X was slowed to appropriate airspeed and descended to 7000. Air carrier X was descended to wrong altitude not in accordance with SOP. SOP calls for downwind to descend to 8000. Error was made by controller, even missed it on readback. Both aircraft were switched to final controller who noticed the downwind air carrier X through 8000, then assigned the right altitude after loss of separation with aircraft Y. Downwind air carrier X on tape replay never made frequency contact with final controller. It's quite possible had air carrier X called on frequency, this would have been caught.

Original NASA ASRS Text

Title: ACR X DSCNT TO OCCUPIED ALT HAD LTSS FROM ACFT Y. SYS ERROR.

Narrative: 2 ACFT ARRIVING DTW, BASE LEG TFC DSNDING TO 7000 ACCORDING TO SOP. DOWNWIND ACR X WAS SLOWED TO APPROPRIATE AIRSPD AND DSNDED TO 7000. ACR X WAS DSNDED TO WRONG ALT NOT IN ACCORDANCE WITH SOP. SOP CALLS FOR DOWNWIND TO DSND TO 8000. ERROR WAS MADE BY CTLR, EVEN MISSED IT ON READBACK. BOTH ACFT WERE SWITCHED TO FINAL CTLR WHO NOTICED THE DOWNWIND ACR X THROUGH 8000, THEN ASSIGNED THE RIGHT ALT AFTER LOSS OF SEPARATION WITH ACFT Y. DOWNWIND ACR X ON TAPE REPLAY NEVER MADE FREQ CONTACT WITH FINAL CTLR. IT'S QUITE POSSIBLE HAD ACR X CALLED ON FREQ, THIS WOULD HAVE BEEN CAUGHT.

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.

Air carrier X descent to occupied altitude had less than standard separation from aircraft Y. System error.