Narrative:

While on an instrument approach to runway 06L at cle; we experienced a loss of localizer and GS prior to the final approach fix (sasco int) and hados intersection. We were established on the localizer and GS was intercepting; descending out of 3000 feet when the aircraft began to pitch up and down with the autopilot engaged. We noticed the localizer frequency on nav 1 had change to a VOR frequency (108.??); the localizer and GS pointers were going left to right full scale on the localizer and up and down full scale on the GS. The autopilot began chasing the GS causing the airplane to change pitch up and down; gradually increasing in intensity. I told the first officer we were going missed as I disengaged the auto pilot to hand fly the airplane and execute the missed approach. Before I disengaged the autopilot; the airplane had pitched up and I disengaged the autopilot applied forward pressure to level off. The first officer called ATC and reported we were executing the missed approach. We were instructed to climb to 3000 feet on an assigned heading. At the time we were approximately at 3400 feet and with the trim that the autopilot had applied; we were climbing at a pretty good rate. By the time I got the trim out and the airplane descending to 3000 feet; we were at 4200 feet. ATC came back and instructed us to maintain 4000 feet. We maintain the heading of the alternate missed approach instructions but not our altitude do to the pitch attitude of the airplane and the back pressure applied by the autopilot. Once I had a feel of the airplane we maintained 4000 feet and proceeded to get vectored around for the ILS to 06R this time instead of 06L. We informed ATC of the loss of navigation (localizer and GS) on the ILS for 06L as the reason for the missed approach. After landing on runway 06R; tower controller apologized about the issue with the ILS and mentioned they received an alert regarding the ILS at the same time we called the missed approached. The ILS for 06L was then NOTAM inop. It appears there was an issue with the ILS signal that cause the collins pro line to lose the localizer frequency and revert or default to the VOR frequency. We had not yet extended the gear or full flaps at the time of losing the GS. I preformed the missed and failed to notice the first officer had not retracted the flaps from approach to the up position; while descending back down to the originally assigned 3000 feet altitude; we received instructions to maintain 4000 feet. I believe this contributed to us climbing at a higher rate than I expected making it more difficult to maintain and descended to the originally assigned 3000 feet. It was during the after takeoff/go around checklist that the flaps were noticed at the approach position.I feel I could have abandoned the approach a few seconds sooner and this may have prevented the airplane from chasing the glide slope to the point of pitching up and down as much as it did and adding so much nose up elevator pressure and trim. I should have checked the flap position sooner and that may have helped me maintain altitude sooner and with less deviation. [The next day] I checked the NOTAMS for cle and it showed the ILS 06L inop.

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Original NASA ASRS Text

Title: An air taxi flight crew reported an issue with the ILS Runway 6L signal at CLE that caused an unexpected pitch up and down with the autopilot engaged.

Narrative: While on an instrument approach to runway 06L at CLE; we experienced a loss of LOC and GS prior to the final approach fix (Sasco int) and Hados intersection. We were established on the LOC and GS was intercepting; descending out of 3000 feet when the aircraft began to pitch up and down with the autopilot engaged. We noticed the LOC frequency on Nav 1 had change to a VOR frequency (108.??); the LOC and GS pointers were going left to right full scale on the LOC and up and down full scale on the GS. The autopilot began chasing the GS causing the airplane to change pitch up and down; gradually increasing in intensity. I told the First officer we were going missed as I disengaged the auto pilot to hand fly the airplane and execute the missed approach. Before I disengaged the autopilot; the airplane had pitched up and I disengaged the autopilot applied forward pressure to level off. The First Officer called ATC and reported we were executing the missed approach. We were instructed to climb to 3000 feet on an assigned heading. At the time we were approximately at 3400 feet and with the trim that the autopilot had applied; we were climbing at a pretty good rate. By the time I got the trim out and the airplane descending to 3000 feet; we were at 4200 feet. ATC came back and instructed us to maintain 4000 feet. We maintain the heading of the alternate missed approach instructions but not our altitude do to the pitch attitude of the airplane and the back pressure applied by the autopilot. Once I had a feel of the airplane we maintained 4000 feet and proceeded to get vectored around for the ILS to 06R this time instead of 06L. We informed ATC of the loss of navigation (LOC and GS) on the ILS for 06L as the reason for the missed approach. After landing on Runway 06R; tower controller apologized about the issue with the ILS and mentioned they received an alert regarding the ILS at the same time we called the missed approached. The ILS for 06L was then NOTAM inop. It appears there was an issue with the ILS signal that cause the Collins Pro Line to lose the LOC frequency and revert or default to the VOR frequency. We had not yet extended the gear or full flaps at the time of losing the GS. I preformed the missed and failed to notice the FO had not retracted the flaps from Approach to the Up position; while descending back down to the originally assigned 3000 feet altitude; we received instructions to maintain 4000 feet. I believe this contributed to us climbing at a higher rate than I expected making it more difficult to maintain and descended to the originally assigned 3000 feet. It was during the After Takeoff/Go Around checklist that the flaps were noticed at the Approach position.I feel I could have abandoned the approach a few seconds sooner and this may have prevented the airplane from chasing the glide slope to the point of pitching up and down as much as it did and adding so much nose up elevator pressure and trim. I should have checked the flap position sooner and that may have helped me maintain altitude sooner and with less deviation. [The next day] I checked the NOTAMS for CLE and it showed the ILS 06L inop.

Data retrieved from NASA's ASRS site 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.