Aircraft equipment problem -- deviation from clearance -- air carrier losses its primary navigation system and drifts off course while trouble- shooting.

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Attributes
ACN	308064
Time
Date	199506
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : tlh
State Reference	FL
Altitude	msl bound lower : 33000 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zjx
Operator	common carrier : air carrier
Make Model Name	B727 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise other
Route In Use	enroute : direct enroute airway : zjx
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 130 flight time total : 15000 flight time type : 3000
ASRS Report	308064
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 130 flight time total : 10000 flight time type : 600
ASRS Report	308612
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance other anomaly other other spatial deviation
Independent Detector	aircraft equipment other aircraft equipment : unspecified 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:

At approximately XA02Z omega navigation system showed ambiguity (ambiguity) on warning indicator. Our airlines pilot's operation manual procedure says to wait 15 mins to see if ambiguity warning extinguishes before resetting the system. After 10 mins. We were informed by ZJX to turn left to a heading of 060 degrees out of an active warning area. I then mentioned to him that we had been cleared 'direct to hevvn intersection' by previous controller. He then informed we were proceeding direct 'leggt' intersection (south of hevvn). It appears the omega navigation system turned us slightly south while in ambiguity mode. We followed ATC instructions and flight proceeded normally.

Original NASA ASRS Text

Title: ACFT EQUIP PROB -- DEV FROM CLRNC -- ACR LOSSES ITS PRIMARY NAV SYS AND DRIFTS OFF COURSE WHILE TROUBLE- SHOOTING.

Narrative: AT APPROX XA02Z OMEGA NAV SYS SHOWED AMB (AMBIGUITY) ON WARNING INDICATOR. OUR AIRLINES PLT'S OP MANUAL PROC SAYS TO WAIT 15 MINS TO SEE IF AMBIGUITY WARNING EXTINGUISHES BEFORE RESETTING THE SYS. AFTER 10 MINS. WE WERE INFORMED BY ZJX TO TURN L TO A HDG OF 060 DEGS OUT OF AN ACTIVE WARNING AREA. I THEN MENTIONED TO HIM THAT WE HAD BEEN CLRED 'DIRECT TO HEVVN INTXN' BY PREVIOUS CTLR. HE THEN INFORMED WE WERE PROCEEDING DIRECT 'LEGGT' INTXN (S OF HEVVN). IT APPEARS THE OMEGA NAV SYS TURNED US SLIGHTLY S WHILE IN AMBIGUITY MODE. WE FOLLOWED ATC INSTRUCTIONS AND FLT PROCEEDED NORMALLY.

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.