Md-11 first officer reported the autopilot deviated below glide slope on approach. They got a glides...

Attributes
ACN	976666
Time
Date	201110
Local Time Of Day	1801-2400
Place
Locale Reference	RKSI.Airport
State Reference	FO
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Make Model Name	MD-11
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Route In Use	Visual Approach
Flight Plan	IFR
Person 1
Function	Pilot Not Flying First Officer
Qualification	Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine Flight Crew Flight Instructor
Experience	Flight Crew Last 90 Days 120 Flight Crew Total 5500
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy Deviation - Procedural Clearance Inflight Event / Encounter CFTT / CFIT

Narrative:

On arrival with captain flying; we monitored ILS glideslope capture at about 1;500 MSL. Descending through 1;200 MSL and in visual conditions; the aircraft began to deviate from the electronic glideslope. Passing through 900 MSL (and coincident to receipt of a 'glideslope' GPWS alert); the captain disconnected the autopilot; corrected the deviation condition; and hand-flew the remainder of the arrival. Also coincident with receipt of the GPWS caution; the tower issued a low-altitude alert of which we were already aware and monitoring. Aircraft was stable by 700 ft AGL (700 ft MSL as well in this case); within the parameters of our stabilized approach criteria. We could have caught the situation sooner and discontinued a coupled approach prior to excessive deviation. Fatigue was a contributing factor; as was a desire to figure out what was causing the deviation.

Original NASA ASRS Text

Title: MD-11 First Officer reported the autopilot deviated below glide slope on approach. They got a GLIDESLOPE GPWS alert; as well as a call from the Tower. They disconnected the autopilot and returned to normal glide path for a landing.

Narrative: On arrival with Captain flying; we monitored ILS glideslope capture at about 1;500 MSL. Descending through 1;200 MSL and in visual conditions; the aircraft began to deviate from the electronic glideslope. Passing through 900 MSL (and coincident to receipt of a 'GLIDESLOPE' GPWS alert); the Captain disconnected the autopilot; corrected the deviation condition; and hand-flew the remainder of the arrival. Also coincident with receipt of the GPWS caution; the Tower issued a low-altitude alert of which we were already aware and monitoring. Aircraft was stable by 700 FT AGL (700 FT MSL as well in this case); within the parameters of our stabilized approach criteria. We could have caught the situation sooner and discontinued a coupled approach prior to excessive deviation. Fatigue was a contributing factor; as was a desire to figure out what was causing the deviation.

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.

Md-11 first officer reported the autopilot deviated below glide slope on approach. They got a glideslope GPWS alert; as well as a call from the tower. They disconnected the autopilot and returned to normal glide path for a landing.