Narrative:

All, up to localizer intercept at geg runway 3, was normal. Cleared ILS runway 3 at approximately XX40 pm local. ILS was armed at 5000 ft MSL, I believe, on a vector heading to intercept ILS. I believe that the aircraft initially captured the localizer and began a series of 'south' turns through the localizer outside of the OM. Drift from the pms was 9-10 degrees left (right crab). GS captured and for some reason aircraft autoplt then went to an altitude hold mode. I believe, at that time, we were right of localizer centerline. I rearmed the ILS and both localizer and GS recaptured. This occurred just inside the OM I believe. Another series of 'south' turns ensued at up to 30 degrees of bank. At approximately 3400 ft MSL 1 DOT deflection left of the localizer, and in a 30 degree right bank, I initiated a map. All questions to tower concerning ILS critical area, ILS function, etc, indicated normal operation. We climbed to 6000 ft MSL and were vectored around for another approach. On a 20-30 degree intercept vector we were cleared for the ILS again, drift was again 9-10 degrees left. Approach then asked if we showed ourselves on localizer centerline. We said no, as CDI casebreak had not yet occurred. My response to approach was, why? Did he show us on centerline? He said no, that it looked like we were parallelling the localizer somewhat. Localizer captured outside the OM and was slightly unstable, but probably normal given the amount of drift that was present, the remainder of the approach was normal and we broke out of minimums and landed on runway 3. My decision to not report via a company report was due to the fact that we, at this time, have nothing to report, since both aircraft system and ILS system operated normally on subsequent approach, and ATC reported that ILS was normal on both approachs. Callback conversation with reporter revealed the following information: he firmly believes that there had been an intrusion into the ILS critical holding area. The tower was reporting a 6000 ft RVR. The actual RVR was 2000 ft. The ground holding position may then have been violated by holding aircraft. The tower was really not capable of observing other aircraft in the holding area due to the reduced visibility and 'sent' someone down to check on that area, but after the fact. Another company aircraft had been making approachs to runway 3/21 all day at an earlier time and reported no problems with the ILS itself. Reporter could not explain the other aircraft equipment anomalies that were exhibited.

Google
 

Original NASA ASRS Text

Title: UNACCEPTABLE GYRATIONS DURING A COUPLED ILS APCH INTO GEG, WA. MAP PERFORMED.

Narrative: ALL, UP TO LOC INTERCEPT AT GEG RWY 3, WAS NORMAL. CLRED ILS RWY 3 AT APPROX XX40 PM LCL. ILS WAS ARMED AT 5000 FT MSL, I BELIEVE, ON A VECTOR HEADING TO INTERCEPT ILS. I BELIEVE THAT THE ACFT INITIALLY CAPTURED THE LOC AND BEGAN A SERIES OF 'S' TURNS THROUGH THE LOC OUTSIDE OF THE OM. DRIFT FROM THE PMS WAS 9-10 DEGS L (R CRAB). GS CAPTURED AND FOR SOME REASON ACFT AUTOPLT THEN WENT TO AN ALT HOLD MODE. I BELIEVE, AT THAT TIME, WE WERE R OF LOC CTRLINE. I REARMED THE ILS AND BOTH LOC AND GS RECAPTURED. THIS OCCURRED JUST INSIDE THE OM I BELIEVE. ANOTHER SERIES OF 'S' TURNS ENSUED AT UP TO 30 DEGS OF BANK. AT APPROX 3400 FT MSL 1 DOT DEFLECTION L OF THE LOC, AND IN A 30 DEG R BANK, I INITIATED A MAP. ALL QUESTIONS TO TWR CONCERNING ILS CRITICAL AREA, ILS FUNCTION, ETC, INDICATED NORMAL OP. WE CLBED TO 6000 FT MSL AND WERE VECTORED AROUND FOR ANOTHER APCH. ON A 20-30 DEG INTERCEPT VECTOR WE WERE CLRED FOR THE ILS AGAIN, DRIFT WAS AGAIN 9-10 DEGS L. APCH THEN ASKED IF WE SHOWED OURSELVES ON LOC CTRLINE. WE SAID NO, AS CDI CASEBREAK HAD NOT YET OCCURRED. MY RESPONSE TO APCH WAS, WHY? DID HE SHOW US ON CTRLINE? HE SAID NO, THAT IT LOOKED LIKE WE WERE PARALLELLING THE LOC SOMEWHAT. LOC CAPTURED OUTSIDE THE OM AND WAS SLIGHTLY UNSTABLE, BUT PROBABLY NORMAL GIVEN THE AMOUNT OF DRIFT THAT WAS PRESENT, THE REMAINDER OF THE APCH WAS NORMAL AND WE BROKE OUT OF MINIMUMS AND LANDED ON RWY 3. MY DECISION TO NOT RPT VIA A COMPANY RPT WAS DUE TO THE FACT THAT WE, AT THIS TIME, HAVE NOTHING TO RPT, SINCE BOTH ACFT SYS AND ILS SYS OPERATED NORMALLY ON SUBSEQUENT APCH, AND ATC RPTED THAT ILS WAS NORMAL ON BOTH APCHS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: HE FIRMLY BELIEVES THAT THERE HAD BEEN AN INTRUSION INTO THE ILS CRITICAL HOLDING AREA. THE TWR WAS RPTING A 6000 FT RVR. THE ACTUAL RVR WAS 2000 FT. THE GND HOLDING POS MAY THEN HAVE BEEN VIOLATED BY HOLDING ACFT. THE TWR WAS REALLY NOT CAPABLE OF OBSERVING OTHER ACFT IN THE HOLDING AREA DUE TO THE REDUCED VISIBILITY AND 'SENT' SOMEONE DOWN TO CHK ON THAT AREA, BUT AFTER THE FACT. ANOTHER COMPANY ACFT HAD BEEN MAKING APCHS TO RWY 3/21 ALL DAY AT AN EARLIER TIME AND RPTED NO PROBS WITH THE ILS ITSELF. RPTR COULD NOT EXPLAIN THE OTHER ACFT EQUIP ANOMALIES THAT WERE EXHIBITED.

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.