Corp mdt track deviation north atlantic.

Attributes
ACN	98406
Time
Date	198811
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : yqx
State Reference	FO
Altitude	msl bound lower : 39000 msl bound upper : 39000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : czqx
Operator	general aviation : corporate
Make Model Name	Medium Transport
Navigation In Use	Other Other
Flight Phase	cruise other
Route In Use	enroute : other oceanic enroute : atlantic
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 90 flight time total : 13000 flight time type : 3000
ASRS Report	98406
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
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

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 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.