An md-80 captain reported an unreliable glideslope on approach to ord. The tower indicated they were...

Narrative:

During our ILS approach to runway 28 at ord in IMC; the first officer's glideslope indicator and my glideslope indicator started to oscillate 1/2 dot above and 1/2 dot below the glideslope; followed by an immediate 2 dot below glideslope indication. At this time we broke out to VMC and saw the runway and VASI lights. We immediately corrected back to the glideslope using the VASI lights and landed without further incident. We reported our glideslope irregularity to ord tower and they stated that they did not have to protect the ILS critical area because the weather was above the requirements. The weather was 5SM 007 ovc. Note: aircraft behind us on the same approach stated that they had problem with the glideslope the same time we did. We also noted an aircraft crossing the approach end of runway 28 when we broke out to VMC.

Original NASA ASRS Text

Title: An MD-80 Captain reported an unreliable glideslope on approach to ORD. The tower indicated they were not required to protect the signal even though the weather was reported to be 700 and 5.

Narrative: During our ILS approach to Runway 28 at ORD in IMC; the First Officer's glideslope indicator and my glideslope indicator started to oscillate 1/2 dot above and 1/2 dot below the glideslope; followed by an immediate 2 dot below glideslope indication. At this time we broke out to VMC and saw the runway and VASI Lights. We immediately corrected back to the glideslope using the VASI Lights and landed without further incident. We reported our glideslope irregularity to ORD Tower and they stated that they did not have to protect the ILS Critical Area because the weather was above the requirements. The weather was 5SM 007 OVC. Note: aircraft behind us on the same approach stated that they had problem with the glideslope the same time we did. We also noted an aircraft crossing the approach end of Runway 28 when we broke out to VMC.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	868000
Time
Date	200912
Local Time Of Day	0601-1200
Place
Locale Reference	ORD.Airport
State Reference	IL
Aircraft 1
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Flight Plan	IFR
Person 1
Function	Captain Pilot Flying
Events
Anomaly	ATC Issue All Types Inflight Event / Encounter Other / Unknown

An md-80 captain reported an unreliable glideslope on approach to ord. The tower indicated they were not required to protect the signal even though the weather was reported to be 700 and 5.