Narrative:

Flight was cleared by approach control for the ILS prm approach to runway 27L at atl. Intercept heading was issued and cleared to intercept glideslope at 7;000 ft on approximately 15-20 mile final. Weather had rain in the vicinity and a frontal line of weather headed to the area with associated clouds. ATIS was issued as special: winds 190-16-gusting 24 (direct crosswind); 1;300 ft broken; 2;000 ft broken; 5;000 ft overcast with visibilities 10 miles. We did not have the runway in sight until late on the approach and had experienced light to occasional moderate turbulence on the approach right up to landing. While on autopilot; the aircraft intercepted the localizer and glideslope almost simultaneously. As the aircraft turned and descended; the aircraft started to pitch up and down rather rapidly to the point of making the ride almost unbearable. The glideslope indications on our instruments showed dead center with no deviations. As the porpoising continued; I elected to disconnect the autopilot and hand fly it down; believing it may be an autopilot maintenance issue. As we continued with an average usual pitch rate (700-800 FPM) down; the glideslope moved up and down throughout the approach and I corrected manually believing it was due to shear from the 53 KT wind on approach at altitude and the approaching front. As we broke out of the clouds at approximately 1;100 ft (3-4 mile final) we picked up the runway visually and I flew the PAPI which showed 2 red and 2 white on the visual portion of the approach. The glideslope then started to show rapid deviations up and down while the airplane's glideslope warning display flashed yellow showing the pilot the deviation. I disregarded the information on the display and continued to visually fly using the PAPI which showed us 2 red and 2 white on glideslope. As we were inside of 1 mile; I observed 2 large john deere style tractors mowing immediately in front and one behind the glideslope antenna for 27L. Landing continued with a normal touchdown and clearing of the runway. On leaving the runway and receiving our hold short instructions for 27R; I advised the controller that we had been receiving glideslope deviations all the way down the approach and that the mowers were probably to blame. He replied 'roger' and we switched frequencies.first point; neither the NOTAMS nor the ATIS ever listed 'men and equipment' in the vicinity of the runways so we had no idea that the mowers could have even been a threat. I have to question the idea of actually allowing mowing equipment in front of the glideslope area while using ILS prm approaches during marginal VFR conditions where that glideslope indication is most needed and important. Since the equipment was in between runways 27L and 27R which were both in use; someone had to know they were there and did not pass along the information. Perhaps a review of when not to mow would be good for the airport operator.

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Original NASA ASRS Text

Title: A pilot flying a PRM approach to ATL Runway 27L saw rapid glideslope fluctuations so he disconnected the autopilot and hand flew the aircraft to VMC at about 1;100 FT. On short final he saw two mowing tractors in front the ILS antenna.

Narrative: Flight was cleared by Approach Control for the ILS PRM approach to Runway 27L at ATL. Intercept heading was issued and cleared to intercept glideslope at 7;000 FT on approximately 15-20 mile final. Weather had rain in the vicinity and a frontal line of weather headed to the area with associated clouds. ATIS was issued as special: Winds 190-16-gusting 24 (direct crosswind); 1;300 FT broken; 2;000 FT broken; 5;000 FT overcast with visibilities 10 miles. We did not have the runway in sight until late on the approach and had experienced light to occasional moderate turbulence on the approach right up to landing. While on autopilot; the aircraft intercepted the localizer and glideslope almost simultaneously. As the aircraft turned and descended; the aircraft started to pitch up and down rather rapidly to the point of making the ride almost unbearable. The glideslope indications on our instruments showed dead center with no deviations. As the porpoising continued; I elected to disconnect the autopilot and hand fly it down; believing it may be an autopilot maintenance issue. As we continued with an average usual pitch rate (700-800 FPM) down; the glideslope moved up and down throughout the approach and I corrected manually believing it was due to shear from the 53 KT wind on approach at altitude and the approaching front. As we broke out of the clouds at approximately 1;100 FT (3-4 mile final) we picked up the runway visually and I flew the PAPI which showed 2 red and 2 white on the visual portion of the approach. The glideslope then started to show rapid deviations up and down while the airplane's glideslope warning display flashed yellow showing the pilot the deviation. I disregarded the information on the display and continued to visually fly using the PAPI which showed us 2 RED and 2 WHITE on glideslope. As we were inside of 1 mile; I observed 2 large John Deere style tractors mowing immediately in front and one behind the glideslope antenna for 27L. Landing continued with a normal touchdown and clearing of the runway. On leaving the runway and receiving our hold short instructions for 27R; I advised the Controller that we had been receiving glideslope deviations all the way down the approach and that the mowers were probably to blame. He replied 'Roger' and we switched frequencies.First point; neither the NOTAMS nor the ATIS ever listed 'men and equipment' in the vicinity of the runways so we had no idea that the mowers could have even been a threat. I have to question the idea of actually allowing mowing equipment in front of the glideslope area while using ILS PRM approaches during marginal VFR conditions where that glideslope indication is most needed and important. Since the equipment was in between Runways 27L and 27R which were both in use; someone had to know they were there and did not pass along the information. Perhaps a review of when NOT to mow would be good for the airport operator.

Data retrieved from NASA's ASRS site as of July 2013 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.