Unknown air carrier aircraft and a DC9 had a TCASII RA at dtw.

Attributes
ACN	420928
Time
Date	199811
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dtw airport : dtw
State Reference	MI
Altitude	msl bound lower : 1650 msl bound upper : 1650
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : dtw
Operator	common carrier : air carrier
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Navigation In Use	Other Other
Flight Phase	descent : approach
Flight Plan	IFR
Aircraft 2
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : cfi
Experience	flight time last 90 days : 270 flight time total : 3000 flight time type : 450
ASRS Report	420928
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 other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : took evasive action other
Consequence	Other
Miss Distance	horizontal : 3500 vertical : 0
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	Intra Facility Coordination Failure Operational Error

Narrative:

We were air carrier flight XXX inbound to dtw from dlh. It was a cavu day and we were cleared for visual runway 21R by tower frequency 135.00. About 4 mi out he asked us if we could accept the center runway which we agreed and started a sidestep to 21C. After established on profile runway 21C the TCASII yelled 'traffic,' illuminated an aircraft in yellow right over us on the screen. It was difficult trying to figure out where he was. A couple of seconds later, TCASII RA of 'descend, descend!' we were too low to descend, so I started a bank back to the right towards runway 21R knowing no one was out there. My captain then looked out his left window and slightly behind us saw air carrier Y (DC9) bank away from us back to the east toward runway 21C. At that instant the DC9 crew asked tower 118.4 'hey, what's that air carrier doing on the center?' the controller responded 'sorry, he was cleared for the center runway first, that was our mistake.' by the way, prior to this TCASII RA we were cleared to land by the tower controller on the center runway 21C (frequency 118.4). My belief is that the 2 tower controllers simply forgot to communicate to each other that they both intended on clearing their aircraft to step over to the runway 21C.

Original NASA ASRS Text

Title: UNKNOWN ACR ACFT AND A DC9 HAD A TCASII RA AT DTW.

Narrative: WE WERE ACR FLT XXX INBOUND TO DTW FROM DLH. IT WAS A CAVU DAY AND WE WERE CLRED FOR VISUAL RWY 21R BY TWR FREQ 135.00. ABOUT 4 MI OUT HE ASKED US IF WE COULD ACCEPT THE CTR RWY WHICH WE AGREED AND STARTED A SIDESTEP TO 21C. AFTER ESTABLISHED ON PROFILE RWY 21C THE TCASII YELLED 'TFC,' ILLUMINATED AN ACFT IN YELLOW RIGHT OVER US ON THE SCREEN. IT WAS DIFFICULT TRYING TO FIGURE OUT WHERE HE WAS. A COUPLE OF SECONDS LATER, TCASII RA OF 'DSND, DSND!' WE WERE TOO LOW TO DSND, SO I STARTED A BANK BACK TO THE R TOWARDS RWY 21R KNOWING NO ONE WAS OUT THERE. MY CAPT THEN LOOKED OUT HIS L WINDOW AND SLIGHTLY BEHIND US SAW ACR Y (DC9) BANK AWAY FROM US BACK TO THE E TOWARD RWY 21C. AT THAT INSTANT THE DC9 CREW ASKED TWR 118.4 'HEY, WHAT'S THAT ACR DOING ON THE CTR?' THE CTLR RESPONDED 'SORRY, HE WAS CLRED FOR THE CTR RWY FIRST, THAT WAS OUR MISTAKE.' BY THE WAY, PRIOR TO THIS TCASII RA WE WERE CLRED TO LAND BY THE TWR CTLR ON THE CTR RWY 21C (FREQ 118.4). MY BELIEF IS THAT THE 2 TWR CTLRS SIMPLY FORGOT TO COMMUNICATE TO EACH OTHER THAT THEY BOTH INTENDED ON CLRING THEIR ACFT TO STEP OVER TO THE RWY 21C.

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.