Narrative:

The flight was normal and uneventful until the final approach segment. The ATIS weather was [visibility] 3; -sn with sct 1;400 broken 2;600. The autopilot properly captured the localizer (localizer) and the glide slope at the final approach fix and remained stable for several seconds.about the time we finished configuring flaps 40; the glide slope abruptly dove down to indicate the aircraft was one to two dots high. The 'a' autopilot was engaged and immediately started a steep dive to 'chase' the glide slope. The pitch dove to around 10 to 12 degrees nose down and the sink rate reached around 2;000 FPM. At this point; the captain disconnected the autopilot and leveled the aircraft. We were around 800 to 1;000 ft AGL and had ground contact but didn't have the runway in sight.I said to the captain that this 'was not working out' and that I thought we should go around. The glide slope then abruptly jumped full scale high indicating that we were now well below glide path. It seemed obvious to me that a go-around was the best course of action. The captain made some comment equivalent to 'not yet' which I interpreted to mean that he was not going to go around.I decided to ask the tower controller to see if he was getting any glide slope alerts. The controller said no but that a heavy airbus had just departed and the ILS critical area was not in effect. At about that time; we acquired the runway in sight and the captain established a descent on the papis along with a now normal glide slope signal. At 500 ft AGL; we realized we had not completed the landing check and accomplished the checklist at that time. The landing was normal and uneventfulthe main thing that I would like to point out about this event is that the aircraft entered a dangerous dive because of a faulty glide slope signal. I can only speculate that the flight would have been in serious danger had the captain not disconnected the autopilot when he did. In my many years of flying; I have rarely; if ever; seen a glide slope signal become so dangerously erratic especially for a flight at night IMC. This should be looked into further. As far as our crew response goes; I believed we reacted improperly. We debriefed this event for quite some time after the flight. We should have gone around. The captain had rationalized his reasons to continue the approach and I had failed to clearly and properly call for a go-around.

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Original NASA ASRS Text

Title: A B737-300 encountered glide slope anomalies which caused erratic pitch responses from the coupled autopilot when a heavy aircraft departing the runway apparently interfered with the glide slope signal. After the departure the glide slope signal returned to normal and the flight landed safely.

Narrative: The flight was normal and uneventful until the final approach segment. The ATIS weather was [visibility] 3; -SN with SCT 1;400 BKN 2;600. The autopilot properly captured the LOC (Localizer) and the glide slope at the final approach fix and remained stable for several seconds.About the time we finished configuring flaps 40; the glide slope abruptly dove down to indicate the aircraft was one to two dots high. The 'A' autopilot was engaged and immediately started a steep dive to 'chase' the glide slope. The pitch dove to around 10 to 12 degrees nose down and the sink rate reached around 2;000 FPM. At this point; the Captain disconnected the autopilot and leveled the aircraft. We were around 800 to 1;000 FT AGL and had Ground contact but didn't have the runway in sight.I said to the Captain that this 'was not working out' and that I thought we should go around. The glide slope then abruptly jumped full scale high indicating that we were now well below glide path. It seemed obvious to me that a go-around was the best course of action. The Captain made some comment equivalent to 'not yet' which I interpreted to mean that he was not going to go around.I decided to ask the Tower Controller to see if he was getting any glide slope alerts. The Controller said no but that a heavy Airbus had just departed and the ILS critical area was not in effect. At about that time; we acquired the runway in sight and the Captain established a descent on the PAPIs along with a now normal glide slope signal. At 500 FT AGL; we realized we had not completed the landing check and accomplished the checklist at that time. The landing was normal and uneventfulThe main thing that I would like to point out about this event is that the aircraft entered a dangerous dive because of a faulty glide slope signal. I can only speculate that the flight would have been in serious danger had the Captain not disconnected the autopilot when he did. In my many years of flying; I have rarely; if ever; seen a glide slope signal become so dangerously erratic especially for a flight at night IMC. This should be looked into further. As far as our crew response goes; I believed we reacted improperly. We debriefed this event for quite some time after the flight. We should have gone around. The Captain had rationalized his reasons to continue the approach and I had failed to clearly and properly call for a go-around.

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.