Heading track deviation makes for a potential conflict or loss of separation on simultaneous ILS app...

Attributes
ACN	189600
Time
Date	199109
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : iah
State Reference	TX
Altitude	msl bound lower : 3000 msl bound upper : 3000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : iah
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 3500 flight time type : 200
ASRS Report	189600
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	conflict : airborne less severe inflight encounter : weather non adherence : clearance other anomaly other other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course other
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were on a 2350 degree heading and cleared to intercept the localizer while conducting an ILS 26 approach at iah. There was a small cell ahead showing 3 levels on our WX radar so the captain turned 10 degree left and just as we were preparing to tell ATC, they called and asked if we were on the 230 heading. I said we deviated slightly and were not back on the 2350 degree heading. He said we were close to an air carrier and gave us a 250 degree heading. The controller asked us to telephone him and proceeded to make a big deal. In the first place, I can't believe the deviation was barely detectable on his radar and secondly we never crossed our localizer so we couldn't have been a hazard to anyone on the parallel ILS 27 approach.

Original NASA ASRS Text

Title: HDG TRACK DEV MAKES FOR A POTENTIAL CONFLICT OR LOSS OF SEPARATION ON SIMULTANEOUS ILS APCH PROC.

Narrative: WE WERE ON A 2350 DEG HDG AND CLRED TO INTERCEPT THE LOC WHILE CONDUCTING AN ILS 26 APCH AT IAH. THERE WAS A SMALL CELL AHEAD SHOWING 3 LEVELS ON OUR WX RADAR SO THE CAPT TURNED 10 DEG L AND JUST AS WE WERE PREPARING TO TELL ATC, THEY CALLED AND ASKED IF WE WERE ON THE 230 HDG. I SAID WE DEVIATED SLIGHTLY AND WERE NOT BACK ON THE 2350 DEG HDG. HE SAID WE WERE CLOSE TO AN ACR AND GAVE US A 250 DEG HDG. THE CTLR ASKED US TO TELEPHONE HIM AND PROCEEDED TO MAKE A BIG DEAL. IN THE FIRST PLACE, I CAN'T BELIEVE THE DEV WAS BARELY DETECTABLE ON HIS RADAR AND SECONDLY WE NEVER CROSSED OUR LOC SO WE COULDN'T HAVE BEEN A HAZARD TO ANYONE ON THE PARALLEL ILS 27 APCH.

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.

Heading track deviation makes for a potential conflict or loss of separation on simultaneous ILS approach procedure.