Air carrier first officer experiences an egpws 'caution obstacle' during a coupled ILS approach to r...

Narrative:

Were cleared for ILS 31R and asked to maintain 170 to datle. Outside of datle; autopilot captured glideslope. After passing datle; I called for flaps 30 then 40. At approximately 2000 ft MSL the glide slope oscillated vertically (as if departing aircraft crossed critical area) and the autopilot increased our rate of descent. Shortly after this we received the GPWS caution 'caution obstacle'. I disconnected autopilot and slowed our descent rate. At this time we were visual and made a normal landing in the touchdown zone. With a heavy aircraft and a slight tailwind on final; our rate of descent contributed to the GPWS caution. Having flown this approach before it was disconcerting to receive this caution while stabilized on the localizer and glideslope with the autopilot coupled. With the tailwind we should not have accepted the 170 knots to datle; which would have allowed us to fully configure prior to datle.

Original NASA ASRS Text

Title: Air carrier First Officer experiences an EGPWS 'caution obstacle' during a coupled ILS approach to Runway 31R at DAL. The glideslope had oscillated up then down and the autopilot followed the glideslope; triggering the caution. The autopilot was disengaged and the approach continued to landing.

Narrative: Were cleared for ILS 31R and asked to maintain 170 to DATLE. Outside of DATLE; autopilot captured glideslope. After passing DATLE; I called for flaps 30 then 40. At approximately 2000 FT MSL the glide slope oscillated vertically (as if departing aircraft crossed critical area) and the autopilot increased our rate of descent. Shortly after this we received the GPWS caution 'Caution Obstacle'. I disconnected autopilot and slowed our descent rate. At this time we were visual and made a normal landing in the touchdown zone. With a heavy aircraft and a slight tailwind on final; our rate of descent contributed to the GPWS caution. Having flown this approach before it was disconcerting to receive this caution while stabilized on the Localizer and glideslope with the autopilot coupled. With the tailwind we should not have accepted the 170 knots to DATLE; which would have allowed us to fully configure prior to DATLE.

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.

Attributes
ACN	1229437
Time
Date	201501
Local Time Of Day	0601-1200
Place
Locale Reference	DAL.Airport
State Reference	TX
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Make Model Name	Large Transport
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Component
Aircraft Component	GPWS
Person 1
Function	Pilot Flying First Officer
Experience	Flight Crew Last 90 Days 192
Events
Anomaly	Inflight Event / Encounter CFTT / CFIT

Air carrier first officer experiences an egpws 'caution obstacle' during a coupled ILS approach to runway 31R at dal. The glideslope had oscillated up then down and the autopilot followed the glideslope; triggering the caution. The autopilot was disengaged and the approach continued to landing.