Corp mdt flies 35-40 miles off course due navigation equipment problem.

Attributes
ACN	179592
Time
Date	199105
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : czqx
State Reference	NF
Altitude	msl bound lower : 41000 msl bound upper : 41000
Aircraft 1
Operator	general aviation : corporate
Make Model Name	Medium Transport
Navigation In Use	Other
Flight Phase	cruise other
Route In Use	enroute : atlantic enroute airway : czqx
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 60 flight time total : 11000 flight time type : 560
ASRS Report	179599
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance other spatial deviation
Independent Detector	other controllera
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	faa : investigated
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Departed shannon for gander, FL410. After about 3:30 hours into the trip, noticed a difference between #1 INS system and #2 vlfirst officermega system. Decision was made to navigation on #1 INS, because it has always been right, knowing that in the past the vlfirst officermega goes D.right. During solar storm activity. This time the vlfirst officermega was right and our INS drifted off (it's over 9 yrs old) (?). Upon radar contact with gander radar, approximately 200 mi, they advised us we were 35-37 NM north of course. We estimated that there was a 10-12 NM difference between our 2 systems. Was advised by gander that they are filing a navigation error report, copy sent to FAA, washington. Received phone call in 5/91 from gander control that the report shows 50 NM north of course, FL410. ATC gander control said 35-37 mi(?). Correction action: systems are being checked and making plans to installed #3 GPS system.

Original NASA ASRS Text

Title: CORP MDT FLIES 35-40 MILES OFF COURSE DUE NAVIGATION EQUIPMENT PROBLEM.

Narrative: DEPARTED SHANNON FOR GANDER, FL410. AFTER ABOUT 3:30 HRS INTO THE TRIP, NOTICED A DIFFERENCE BTWN #1 INS SYS AND #2 VLF/OMEGA SYS. DECISION WAS MADE TO NAV ON #1 INS, BECAUSE IT HAS ALWAYS BEEN RIGHT, KNOWING THAT IN THE PAST THE VLF/OMEGA GOES D.R. DURING SOLAR STORM ACTIVITY. THIS TIME THE VLF/OMEGA WAS RIGHT AND OUR INS DRIFTED OFF (IT'S OVER 9 YRS OLD) (?). UPON RADAR CONTACT WITH GANDER RADAR, APPROX 200 MI, THEY ADVISED US WE WERE 35-37 NM N OF COURSE. WE ESTIMATED THAT THERE WAS A 10-12 NM DIFFERENCE BTWN OUR 2 SYSTEMS. WAS ADVISED BY GANDER THAT THEY ARE FILING A NAV ERROR RPT, COPY SENT TO FAA, WASHINGTON. RECEIVED PHONE CALL IN 5/91 FROM GANDER CTL THAT THE RPT SHOWS 50 NM N OF COURSE, FL410. ATC GANDER CTL SAID 35-37 MI(?). CORRECTION ACTION: SYSTEMS ARE BEING CHKED AND MAKING PLANS TO INSTALLED #3 GPS SYS.

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.