MD80 first officer (PF) misinterpreted an assigned heading of 100 degrees as 010 degrees. Approach controller intervened with a descent and new heading just as flight crew received a TCASII RA. Track deviation caused potential conflict.

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Attributes
ACN	329250
Time
Date	199602
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ord
State Reference	IL
Altitude	msl bound lower : 5000 msl bound upper : 5000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent : approach descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 6000 flight time type : 3000
ASRS Report	329250
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	329322
Events
Anomaly	conflict : airborne less severe non adherence : clearance other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance other
Consequence	Other
Miss Distance	horizontal : 12000 vertical : 1000
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

During downwind approach to ord runway 27L at 5000 ft and heading 090 degrees, we were being vectored to land. About 75 NM out and expecting a left turn to base, I heard the controller turn us to a heading of 010 degrees. I should have verified with the PNF. I turned left and at this point the controller asked where we were going. We verified left to 010 degrees. Apparently he wanted 100 degrees. He immediately requested a descending right turn to 4000 ft and 120 degree heading. TCASII noted traffic and we picked up the traffic visually. During the maneuver TCASII issued a descent, but we were already correcting appropriately. Supplemental information from acn 329322: I, as the PNF, read back turn to 100 degrees and continued the checklist for the approach. When I looked up and saw 010 degrees, I thought 'did they say 100 or 010?' I did not monitor the turn soon enough. The approach controller did everything right. A heading 010 or 100 might have been clrer if I had read back one zero zero one hundred or zero one zero ten.

Original NASA ASRS Text

Title: MD80 FO (PF) MISINTERPRETED AN ASSIGNED HDG OF 100 DEGS AS 010 DEGS. APCH CTLR INTERVENED WITH A DSCNT AND NEW HDG JUST AS FLC RECEIVED A TCASII RA. TRACK DEV CAUSED POTENTIAL CONFLICT.

Narrative: DURING DOWNWIND APCH TO ORD RWY 27L AT 5000 FT AND HDG 090 DEGS, WE WERE BEING VECTORED TO LAND. ABOUT 75 NM OUT AND EXPECTING A L TURN TO BASE, I HEARD THE CTLR TURN US TO A HDG OF 010 DEGS. I SHOULD HAVE VERIFIED WITH THE PNF. I TURNED L AND AT THIS POINT THE CTLR ASKED WHERE WE WERE GOING. WE VERIFIED L TO 010 DEGS. APPARENTLY HE WANTED 100 DEGS. HE IMMEDIATELY REQUESTED A DSNDING R TURN TO 4000 FT AND 120 DEG HDG. TCASII NOTED TFC AND WE PICKED UP THE TFC VISUALLY. DURING THE MANEUVER TCASII ISSUED A DSCNT, BUT WE WERE ALREADY CORRECTING APPROPRIATELY. SUPPLEMENTAL INFO FROM ACN 329322: I, AS THE PNF, READ BACK TURN TO 100 DEGS AND CONTINUED THE CHKLIST FOR THE APCH. WHEN I LOOKED UP AND SAW 010 DEGS, I THOUGHT 'DID THEY SAY 100 OR 010?' I DID NOT MONITOR THE TURN SOON ENOUGH. THE APCH CTLR DID EVERYTHING RIGHT. A HDG 010 OR 100 MIGHT HAVE BEEN CLRER IF I HAD READ BACK ONE ZERO ZERO ONE HUNDRED OR ZERO ONE ZERO TEN.

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.