Gross INS navigation error north atlantic.

Attributes
ACN	293364
Time
Date	199501
Day	Mon
Local Time Of Day	0001 To 0600
Place
Locale Reference	atc facility : eisn
State Reference	FO
Altitude	msl bound lower : 41000 msl bound upper : 41000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	tower : dtw
Operator	general aviation : corporate
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Navigation In Use	Other
Flight Phase	cruise other
Route In Use	enroute : atlantic enroute airway : eisn
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 8000 flight time type : 2010
ASRS Report	293364
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance other anomaly other other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

After crossing north atlantic on route yqx, 51.50, 53.40, 54.30, 54.20, 53.15, burak, einn. Reported 54.20 at air traffic area XA26Z, FL410, ETA 53.15 at XA49Z, burak. Just prior to 53.15 shannon called us on VHF 135.6 and informed us we were off course by 38 mi north. We reviewed his coordinates and compared them with our omegas. We showed we were no more than 5-6 mi north of course. On checking other navigation inputs (#1 IRS and #2 IRS inputs) on the #1 side showed us 35 mi left. #1 IRS and #2 IRS inputs on the right side showed us no more than 2 mi left. We took a heading from shannon and landed with no further comments. Plot at 54.20 was N54.06 - W20.07, #1 side, N54.05, W20.03 #2 side. This was not significant off course for concern. 3 navaids were showing plus or minus 5 mi off course and inbound to N53.W15. We were surprised that just prior to N53.W15 we were informed we were so far off course. At no time prior to 53.15 including our recorded position at N54.20W indicated we had to correct a significant course deviation. Maintenance is checking #1 navigation system for problems. (Suspect #1 VLF.) navigation system will be flight checked prior to next overwater flight.

Original NASA ASRS Text

Title: GROSS INS NAV ERROR NORTH ATLANTIC.

Narrative: AFTER XING NORTH ATLANTIC ON RTE YQX, 51.50, 53.40, 54.30, 54.20, 53.15, BURAK, EINN. RPTED 54.20 AT ATA XA26Z, FL410, ETA 53.15 AT XA49Z, BURAK. JUST PRIOR TO 53.15 SHANNON CALLED US ON VHF 135.6 AND INFORMED US WE WERE OFF COURSE BY 38 MI N. WE REVIEWED HIS COORDINATES AND COMPARED THEM WITH OUR OMEGAS. WE SHOWED WE WERE NO MORE THAN 5-6 MI N OF COURSE. ON CHKING OTHER NAV INPUTS (#1 IRS AND #2 IRS INPUTS) ON THE #1 SIDE SHOWED US 35 MI L. #1 IRS AND #2 IRS INPUTS ON THE R SIDE SHOWED US NO MORE THAN 2 MI L. WE TOOK A HDG FROM SHANNON AND LANDED WITH NO FURTHER COMMENTS. PLOT AT 54.20 WAS N54.06 - W20.07, #1 SIDE, N54.05, W20.03 #2 SIDE. THIS WAS NOT SIGNIFICANT OFF COURSE FOR CONCERN. 3 NAVAIDS WERE SHOWING PLUS OR MINUS 5 MI OFF COURSE AND INBOUND TO N53.W15. WE WERE SURPRISED THAT JUST PRIOR TO N53.W15 WE WERE INFORMED WE WERE SO FAR OFF COURSE. AT NO TIME PRIOR TO 53.15 INCLUDING OUR RECORDED POS AT N54.20W INDICATED WE HAD TO CORRECT A SIGNIFICANT COURSE DEV. MAINT IS CHKING #1 NAV SYS FOR PROBS. (SUSPECT #1 VLF.) NAV SYS WILL BE FLT CHKED PRIOR TO NEXT OVERWATER FLT.

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.