Narrative:

Frequencys set, identify confirmed. Solid soup, OM inbound, 300 hour private pilot instrument student hand flying. Both needles within the inner circle. At 400 ft above decision ht, instructor noted that both needles were 'perfectly centered.' at 300 ft above decision ht instructor saw shoreline pass below as we headed out to sea. During map pilot noticed that the ILS received had changed frequency and both needles still centered, no red flags, both pilots confirmed the condition. The following approach was successful in every way. No identifiable explanation for the frequency change. The 'new' frequency was not the standby frequency. I, the instructor, relayed the event to senior pilots of the local airline. 2 weeks later they noted a similar uncommanded frequency change on a communication frequency. With the reported 20 degrees 13 KT left crosswind, X allowed the airplane to drift to where -- on the GS at 400 ft altitude and still in the soup -- the localizer needle was off scale. We had no choice but to execute a map. The radar operator apologized for turning us on to the localizer a bit too close- in and advised that this time he would position us about 12 mi out. Prior to our second approach, X went through the pre- landing checks again, fuel remaining, 2 hours, frequencys still set, all system operating as expected. The radar operator positioned us at 13 mi from the airport, and we intercepted the localizer at a comfortable 30 degree angle. We intercepted the GS at the OM, X lowered the landing gear and started down toward the published decision ht of 225 ft MSL. Constantly monitoring the pilot's actions, the instrument panel and occasionally out the windows, I was very pleased that X had the localizer and GS needles perfectly centered -- this was a very good approach. As X called off the remaining altitude: '400 ft to go,' '300 ft to go,' '200 ft to go,' I looked ahead and still could see nothing but grey clouds -- then looking down, out my right side window, I noticed trees about 100 ft below just as we crossed the indian ocean shoreline. 'Go around' I commanded, and applied full throttle. X responded by retracting the landing gear and as every good pilot is taught continued to 'fly the airplane.' throughout all of this, both the ILS needles were perfectly centered, then X said 'look, the ILS receiver has changed frequency.' sure enough, instead of 110.3 where it had been set and confirmed, the ILS receiver read 110.7 and there were no red flags to indicate a non-serviceable signal. For the third approach, both X and I carefully reset the ILS frequency, confirmed all the settings and idents and asked for another 12 or 15 mi positioning to intercept the localizer. In nearly 50 yrs of flying I had never seen radios change frequencys 'by themselves' ie, untouched -- oh yes in 'the old days' I and others occasionally bumped the knobs and de- tuned a receiver -- but none of that since digital frequency settings improved our lives. The message is clear, keep your eyes open and be ready for anything. I described our 'frequency change problem' and the accompanying circumstances to one of the senior capts at air carrier Y. He in turn relayed the story to several other flcs at the airline. Just 2 weeks later in mid-jan, they were at cruise altitude in an ATR42 between lusaka, zambia, and lilongwe, malawi, when he noticed the tenths digit (point X) on the standby frequency of their X communication receiver 'rolling upward' ie, point 1, point 2, point 3, point 4, etc. This continued for several mins while he and his copilot watched in awe. These messages are clear -- keep your eyes open and be ready for anything.

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Original NASA ASRS Text

Title: HDG TRACK POS ALTDEV ON ILS APCH IN FOREIGN AIRSPACE.

Narrative: FREQS SET, IDENT CONFIRMED. SOLID SOUP, OM INBOUND, 300 HR PVT PLT INST STUDENT HAND FLYING. BOTH NEEDLES WITHIN THE INNER CIRCLE. AT 400 FT ABOVE DECISION HT, INSTRUCTOR NOTED THAT BOTH NEEDLES WERE 'PERFECTLY CTRED.' AT 300 FT ABOVE DECISION HT INSTRUCTOR SAW SHORELINE PASS BELOW AS WE HEADED OUT TO SEA. DURING MAP PLT NOTICED THAT THE ILS RECEIVED HAD CHANGED FREQ AND BOTH NEEDLES STILL CTRED, NO RED FLAGS, BOTH PLTS CONFIRMED THE CONDITION. THE FOLLOWING APCH WAS SUCCESSFUL IN EVERY WAY. NO IDENTIFIABLE EXPLANATION FOR THE FREQ CHANGE. THE 'NEW' FREQ WAS NOT THE STANDBY FREQ. I, THE INSTRUCTOR, RELAYED THE EVENT TO SENIOR PLTS OF THE LCL AIRLINE. 2 WKS LATER THEY NOTED A SIMILAR UNCOMMANDED FREQ CHANGE ON A COM FREQ. WITH THE RPTED 20 DEGS 13 KT L XWIND, X ALLOWED THE AIRPLANE TO DRIFT TO WHERE -- ON THE GS AT 400 FT ALT AND STILL IN THE SOUP -- THE LOC NEEDLE WAS OFF SCALE. WE HAD NO CHOICE BUT TO EXECUTE A MAP. THE RADAR OPERATOR APOLOGIZED FOR TURNING US ON TO THE LOC A BIT TOO CLOSE- IN AND ADVISED THAT THIS TIME HE WOULD POS US ABOUT 12 MI OUT. PRIOR TO OUR SECOND APCH, X WENT THROUGH THE PRE- LNDG CHKS AGAIN, FUEL REMAINING, 2 HRS, FREQS STILL SET, ALL SYS OPERATING AS EXPECTED. THE RADAR OPERATOR POSITIONED US AT 13 MI FROM THE ARPT, AND WE INTERCEPTED THE LOC AT A COMFORTABLE 30 DEG ANGLE. WE INTERCEPTED THE GS AT THE OM, X LOWERED THE LNDG GEAR AND STARTED DOWN TOWARD THE PUBLISHED DECISION HT OF 225 FT MSL. CONSTANTLY MONITORING THE PLT'S ACTIONS, THE INST PANEL AND OCCASIONALLY OUT THE WINDOWS, I WAS VERY PLEASED THAT X HAD THE LOC AND GS NEEDLES PERFECTLY CTRED -- THIS WAS A VERY GOOD APCH. AS X CALLED OFF THE REMAINING ALT: '400 FT TO GO,' '300 FT TO GO,' '200 FT TO GO,' I LOOKED AHEAD AND STILL COULD SEE NOTHING BUT GREY CLOUDS -- THEN LOOKING DOWN, OUT MY R SIDE WINDOW, I NOTICED TREES ABOUT 100 FT BELOW JUST AS WE CROSSED THE INDIAN OCEAN SHORELINE. 'GAR' I COMMANDED, AND APPLIED FULL THROTTLE. X RESPONDED BY RETRACTING THE LNDG GEAR AND AS EVERY GOOD PLT IS TAUGHT CONTINUED TO 'FLY THE AIRPLANE.' THROUGHOUT ALL OF THIS, BOTH THE ILS NEEDLES WERE PERFECTLY CTRED, THEN X SAID 'LOOK, THE ILS RECEIVER HAS CHANGED FREQ.' SURE ENOUGH, INSTEAD OF 110.3 WHERE IT HAD BEEN SET AND CONFIRMED, THE ILS RECEIVER READ 110.7 AND THERE WERE NO RED FLAGS TO INDICATE A NON-SERVICEABLE SIGNAL. FOR THE THIRD APCH, BOTH X AND I CAREFULLY RESET THE ILS FREQ, CONFIRMED ALL THE SETTINGS AND IDENTS AND ASKED FOR ANOTHER 12 OR 15 MI POSITIONING TO INTERCEPT THE LOC. IN NEARLY 50 YRS OF FLYING I HAD NEVER SEEN RADIOS CHANGE FREQS 'BY THEMSELVES' IE, UNTOUCHED -- OH YES IN 'THE OLD DAYS' I AND OTHERS OCCASIONALLY BUMPED THE KNOBS AND DE- TUNED A RECEIVER -- BUT NONE OF THAT SINCE DIGITAL FREQ SETTINGS IMPROVED OUR LIVES. THE MESSAGE IS CLR, KEEP YOUR EYES OPEN AND BE READY FOR ANYTHING. I DESCRIBED OUR 'FREQ CHANGE PROB' AND THE ACCOMPANYING CIRCUMSTANCES TO ONE OF THE SENIOR CAPTS AT ACR Y. HE IN TURN RELAYED THE STORY TO SEVERAL OTHER FLCS AT THE AIRLINE. JUST 2 WKS LATER IN MID-JAN, THEY WERE AT CRUISE ALT IN AN ATR42 BTWN LUSAKA, ZAMBIA, AND LILONGWE, MALAWI, WHEN HE NOTICED THE TENTHS DIGIT (POINT X) ON THE STANDBY FREQ OF THEIR X COM RECEIVER 'ROLLING UPWARD' IE, POINT 1, POINT 2, POINT 3, POINT 4, ETC. THIS CONTINUED FOR SEVERAL MINS WHILE HE AND HIS COPLT WATCHED IN AWE. THESE MESSAGES ARE CLR -- KEEP YOUR EYES OPEN AND BE READY FOR ANYTHING.

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.