|37000 Feet||Browse and search NASA's
Aviation Safety Reporting System
|Local Time Of Day||0601 To 1200|
|Locale Reference||atc facility : yqx|
|Altitude||msl bound lower : 39000|
msl bound upper : 39000
|Controlling Facilities||artcc : czqx|
|Operator||general aviation : corporate|
|Make Model Name||Medium Transport|
|Navigation In Use||Other |
|Flight Phase||cruise other|
|Route In Use||enroute : other oceanic|
enroute : atlantic
|Function||flight crew : captain|
oversight : pic
|Qualification||pilot : atp|
|Experience||flight time last 90 days : 90|
flight time total : 13000
flight time type : 3000
|Function||flight crew : first officer|
|Qualification||pilot : atp|
|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|
|Air Traffic Incident||Pilot Deviation|
Were reported 17.8 miles north off course at 49/50 enroute from shannon to gander. By gander control was using 2 FMS each with 2 VLF omega, 2 IRS, 2 vpu followed all procedures established by company. First both IRS' drifted off course by 17 miles then came back. VLF's were drifting as well to as much as 22 miles. All of them together not being able to deselect per company procedures we continued on our blended position as described in company FMS flight manual. At gander airport both FMS were off by 12 miles after using the vpu's for 150 miles. This problem was escalated to the top level of management of mfg and company. Presently awaiting answers. Callback conversation with reporter revealed the following: the IRS units were in fact correct and the vlfirst officermega sets were in fact drifting and since company procedure is to fly the VLF since it can direct the a/P by lock on and the inertial cannot. Since this incident the aircraft mfr has flown their test aircraft on the route and found their omega had the same drift problem. Now believe it is an installation problem and the omegas are being affected by the aircraft equipment. In this aircraft they did find occilators in omegas were overheating and causing drift so manufacturer is looking for solution, possibly relocating the omega units which are now located under the middle engine and being affected by engine RF noise. In interim company has changed procedure and using the two inertial sets for primary long range overwater navigation and omega for backup.
Original NASA ASRS Text
Title: CORP MDT TRACK DEVIATION NORTH ATLANTIC.
Narrative: WERE REPORTED 17.8 MILES NORTH OFF COURSE AT 49/50 ENROUTE FROM SHANNON TO GANDER. BY GANDER CONTROL WAS USING 2 FMS EACH WITH 2 VLF OMEGA, 2 IRS, 2 VPU FOLLOWED ALL PROCEDURES ESTABLISHED BY COMPANY. FIRST BOTH IRS' DRIFTED OFF COURSE BY 17 MILES THEN CAME BACK. VLF'S WERE DRIFTING AS WELL TO AS MUCH AS 22 MILES. ALL OF THEM TOGETHER NOT BEING ABLE TO DESELECT PER COMPANY PROCEDURES WE CONTINUED ON OUR BLENDED POSITION AS DESCRIBED IN COMPANY FMS FLIGHT MANUAL. AT GANDER AIRPORT BOTH FMS WERE OFF BY 12 MILES AFTER USING THE VPU'S FOR 150 MILES. THIS PROBLEM WAS ESCALATED TO THE TOP LEVEL OF MGMNT OF MFG AND COMPANY. PRESENTLY AWAITING ANSWERS. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: THE IRS UNITS WERE IN FACT CORRECT AND THE VLF/OMEGA SETS WERE IN FACT DRIFTING AND SINCE COMPANY PROC IS TO FLY THE VLF SINCE IT CAN DIRECT THE A/P BY LOCK ON AND THE INERTIAL CANNOT. SINCE THIS INCIDENT THE ACFT MFR HAS FLOWN THEIR TEST ACFT ON THE ROUTE AND FOUND THEIR OMEGA HAD THE SAME DRIFT PROBLEM. NOW BELIEVE IT IS AN INSTALLATION PROBLEM AND THE OMEGAS ARE BEING AFFECTED BY THE ACFT EQUIPMENT. IN THIS ACFT THEY DID FIND OCCILATORS IN OMEGAS WERE OVERHEATING AND CAUSING DRIFT SO MANUFACTURER IS LOOKING FOR SOLUTION, POSSIBLY RELOCATING THE OMEGA UNITS WHICH ARE NOW LOCATED UNDER THE MIDDLE ENGINE AND BEING AFFECTED BY ENGINE RF NOISE. IN INTERIM COMPANY HAS CHANGED PROC AND USING THE TWO INERTIAL SETS FOR PRIMARY LONG RANGE OVERWATER NAV AND OMEGA FOR BACKUP.
Data retrieved from NASA's ASRS site as of August 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.