Narrative:

In 3/89 at approximately XA50 UTC (Z), while navigating from lax to hnl using a dual omega navigation system, navigation inoperative flags suddenly appeared in the captain's and first officer's HSI. A check of both navigation units revealed that an ambiguity had been sensed. No other flags or indications were given. The crew performed the 'clear ambiguity' procedure set forth in the operating manual. This cleared all lights and flags. At the same time other aircraft on R576 and elsewhere reported an inability to make HF communication contact with ZOA through sfo commercial radio. And through the use of unauthorized communication on 128.95 the communication problems were discussed between various trans-pac flts. Other aircraft (including air carrier C, air carrier D and air carrier east) reported similar navigation problems and annunciations, and all agreed on a general, 'don't follow me, because I don't know where I'm going either,' navigation rule of thumb. At XB12Z (UTC) by constantly monitoring omega wind readout, we determined that the #1 navigation unit was taking off. Winds suddenly indicated a 30 degree shift and an increase from 80 to 150 KTS on the #1 unit while #2 remained steady. First officer elected to stop the #1 omega from an off course shift by using the non approved procedure of entering a 'manual wind' into the #1 unit. This kept both units within 7-9 NM of R576 and each other. And both units appeared normal. At XC03 UTC (Z) the #1 omega unit took off again, with wind direction and speed making a sudden drastic change. First officer again stopped the shift by a manual wind entry on #1, and the captain elected to do a non precision update, using the position indicated on the #2 omega as the reference for position. Navigation continued normal and upon arrival at hnl, #1 omega indicated 4 NM off while #2 omega showed 1 NM off, and both units appeared entirely normal on the return flight to the mainland. Callback conversation with reporter revealed the following: confirmed that solar flare or modal interference was the cause of the problem. Reporter said he has had another incident since this report and notes that the forecast is for the solar activity to increase next year.

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Original NASA ASRS Text

Title: ACR WDB HAD NAVIGATION AND COM PROBLEMS BETWEEN LAX AND HNL. SEVERAL OTHER ACR ACFT IN THE AREA ALSO EXPERIENCED THE SAME PROBLEMS.

Narrative: IN 3/89 AT APPROX XA50 UTC (Z), WHILE NAVIGATING FROM LAX TO HNL USING A DUAL OMEGA NAV SYS, NAV INOP FLAGS SUDDENLY APPEARED IN THE CAPT'S AND F/O'S HSI. A CHK OF BOTH NAV UNITS REVEALED THAT AN AMBIGUITY HAD BEEN SENSED. NO OTHER FLAGS OR INDICATIONS WERE GIVEN. THE CREW PERFORMED THE 'CLEAR AMBIGUITY' PROC SET FORTH IN THE OPERATING MANUAL. THIS CLRED ALL LIGHTS AND FLAGS. AT THE SAME TIME OTHER ACFT ON R576 AND ELSEWHERE RPTED AN INABILITY TO MAKE HF COM CONTACT WITH ZOA THROUGH SFO COMMERCIAL RADIO. AND THROUGH THE USE OF UNAUTH COM ON 128.95 THE COM PROBS WERE DISCUSSED BTWN VARIOUS TRANS-PAC FLTS. OTHER ACFT (INCLUDING ACR C, ACR D AND ACR E) RPTED SIMILAR NAV PROBS AND ANNUNCIATIONS, AND ALL AGREED ON A GENERAL, 'DON'T FOLLOW ME, BECAUSE I DON'T KNOW WHERE I'M GOING EITHER,' NAV RULE OF THUMB. AT XB12Z (UTC) BY CONSTANTLY MONITORING OMEGA WIND READOUT, WE DETERMINED THAT THE #1 NAV UNIT WAS TAKING OFF. WINDS SUDDENLY INDICATED A 30 DEG SHIFT AND AN INCREASE FROM 80 TO 150 KTS ON THE #1 UNIT WHILE #2 REMAINED STEADY. F/O ELECTED TO STOP THE #1 OMEGA FROM AN OFF COURSE SHIFT BY USING THE NON APPROVED PROC OF ENTERING A 'MANUAL WIND' INTO THE #1 UNIT. THIS KEPT BOTH UNITS WITHIN 7-9 NM OF R576 AND EACH OTHER. AND BOTH UNITS APPEARED NORMAL. AT XC03 UTC (Z) THE #1 OMEGA UNIT TOOK OFF AGAIN, WITH WIND DIRECTION AND SPD MAKING A SUDDEN DRASTIC CHANGE. F/O AGAIN STOPPED THE SHIFT BY A MANUAL WIND ENTRY ON #1, AND THE CAPT ELECTED TO DO A NON PRECISION UPDATE, USING THE POS INDICATED ON THE #2 OMEGA AS THE REF FOR POS. NAV CONTINUED NORMAL AND UPON ARR AT HNL, #1 OMEGA INDICATED 4 NM OFF WHILE #2 OMEGA SHOWED 1 NM OFF, AND BOTH UNITS APPEARED ENTIRELY NORMAL ON THE RETURN FLT TO THE MAINLAND. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: CONFIRMED THAT SOLAR FLARE OR MODAL INTERFERENCE WAS THE CAUSE OF THE PROB. RPTR SAID HE HAS HAD ANOTHER INCIDENT SINCE THIS RPT AND NOTES THAT THE FORECAST IS FOR THE SOLAR ACTIVITY TO INCREASE NEXT YEAR.

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.