Narrative:

On a scheduled airline flight from pvd (providence, ri) to rdu (raleigh-durham, nc) while cruising at FL270, the following situation developed. After a complex departure out of pvd, we were cleared direct to natly intersection (which is not programmed into our omega/VLF). We entered its coordinates and proceeded direct to natly. Upon arrival at natly, the omega turned on course sbound down the airway (J174). During the later part of the climb out, the VOR indications had been very erratic and I suspect someone in the cabin was using a cellular telephone or other illegal RF emitter not approved for use and I mentioned this fact as we might want to have the flight attendants check this in the cabin. The NOTAM, issued with our flight plan/release, did not contain any VORTAC outages along our route, but did state that omega polar path disturbances have commenced. Right about the time the flight attendant brought the captain's and flight engineer's lunches and my cup of coffee, the aircraft started in a slow left turn, which I noticed after about 20-30 degrees of heading change. I then disengaged the omega and commenced a right turn back to the airway, and as I did so center issued a 40 degree right turn to reintercept the airway and told us we were 8.2 mi left of centerline. We corrected back using the VOR which was still slightly 'shaky' even though it was well within usable range and had a clear identify. The omega unit showed no malfunction lights or indications prior to or during this time. It was loaded, pre-departure, via ACARS at the gate and all domestic pre-departure checks were performed, each waypoints and coordinates were checked, and at the arrival gate an accuracy check showed a 13.2 NM error, which is, of course unacceptable for use. I do not know if RF emitters in the cabin effect omega in any way. As is often the case, the omega/ulf's many weak points all come together and coupled with a slow heading change point out and reinforce the need for just as great a vigilance as when hand flying VOR airways!

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Original NASA ASRS Text

Title: ACR LGT TRACK HDG DEV USING OMEGA NAV.

Narrative: ON A SCHEDULED AIRLINE FLT FROM PVD (PROVIDENCE, RI) TO RDU (RALEIGH-DURHAM, NC) WHILE CRUISING AT FL270, THE FOLLOWING SITUATION DEVELOPED. AFTER A COMPLEX DEP OUT OF PVD, WE WERE CLRED DIRECT TO NATLY INTXN (WHICH IS NOT PROGRAMMED INTO OUR OMEGA/VLF). WE ENTERED ITS COORDINATES AND PROCEEDED DIRECT TO NATLY. UPON ARR AT NATLY, THE OMEGA TURNED ON COURSE SBOUND DOWN THE AIRWAY (J174). DURING THE LATER PART OF THE CLBOUT, THE VOR INDICATIONS HAD BEEN VERY ERRATIC AND I SUSPECT SOMEONE IN THE CABIN WAS USING A CELLULAR TELEPHONE OR OTHER ILLEGAL RF EMITTER NOT APPROVED FOR USE AND I MENTIONED THIS FACT AS WE MIGHT WANT TO HAVE THE FLT ATTENDANTS CHK THIS IN THE CABIN. THE NOTAM, ISSUED WITH OUR FLT PLAN/RELEASE, DID NOT CONTAIN ANY VORTAC OUTAGES ALONG OUR RTE, BUT DID STATE THAT OMEGA POLAR PATH DISTURBANCES HAVE COMMENCED. RIGHT ABOUT THE TIME THE FLT ATTENDANT BROUGHT THE CAPT'S AND FLT ENGINEER'S LUNCHES AND MY CUP OF COFFEE, THE ACFT STARTED IN A SLOW L TURN, WHICH I NOTICED AFTER ABOUT 20-30 DEGS OF HDG CHANGE. I THEN DISENGAGED THE OMEGA AND COMMENCED A R TURN BACK TO THE AIRWAY, AND AS I DID SO CENTER ISSUED A 40 DEG R TURN TO REINTERCEPT THE AIRWAY AND TOLD US WE WERE 8.2 MI L OF CENTERLINE. WE CORRECTED BACK USING THE VOR WHICH WAS STILL SLIGHTLY 'SHAKY' EVEN THOUGH IT WAS WELL WITHIN USABLE RANGE AND HAD A CLR IDENT. THE OMEGA UNIT SHOWED NO MALFUNCTION LIGHTS OR INDICATIONS PRIOR TO OR DURING THIS TIME. IT WAS LOADED, PRE-DEP, VIA ACARS AT THE GATE AND ALL DOMESTIC PRE-DEP CHKS WERE PERFORMED, EACH WAYPOINTS AND COORDINATES WERE CHKED, AND AT THE ARR GATE AN ACCURACY CHK SHOWED A 13.2 NM ERROR, WHICH IS, OF COURSE UNACCEPTABLE FOR USE. I DO NOT KNOW IF RF EMITTERS IN THE CABIN EFFECT OMEGA IN ANY WAY. AS IS OFTEN THE CASE, THE OMEGA/ULF'S MANY WEAK POINTS ALL COME TOGETHER AND COUPLED WITH A SLOW HDG CHANGE POINT OUT AND REINFORCE THE NEED FOR JUST AS GREAT A VIGILANCE AS WHEN HAND FLYING VOR AIRWAYS!

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.