B737-ng captain reported that an autopilot failure during approach resulted in a firm landing.

Attributes
ACN	1698992
Time
Date	201911
Local Time Of Day	0601-1200
Place
Locale Reference	SEA.Airport
State Reference	WA
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Make Model Name	B737 Next Generation Undifferentiated
Operating Under FAR Part	Part 121
Flight Phase	Final Approach Landing
Flight Plan	IFR
Component
Aircraft Component	Autoland
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Multiengine Flight Crew Air Transport Pilot (ATP) Flight Crew Instrument
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy Ground Event / Encounter Other / Unknown

Narrative:

A3 autoland failure. First officer's leg. Weather was below cat I minimums so we switched to an hgs HUD hybrid autoland; captain flown.engaged second auto pilot on a 10 mile final; had to re-engage both auto pilots and reset both master flight directors twice on the arrival. Prior to entering IMC; as briefed we switched to a heads up display arrival with increased minimums when the autoland autopilot system failed again. Shortly after that I received an approach warning in the heads up display; and with the approach lights [and] runway in sight; we completed the landing.the landing was on center line; but very firm. The taxi and shut down after that the normal. We wrote up the A3 automated system; and put it in the book. We debriefed the landing for the passengers and the crew.maintenance is going to investigate the HUD; A3; and autopilot.

Original NASA ASRS Text

Title: B737-NG Captain reported that an autopilot failure during approach resulted in a firm landing.

Narrative: A3 autoland failure. First Officer's leg. Weather was below Cat I minimums so we switched to an HGS HUD hybrid autoland; Captain flown.Engaged second auto pilot on a 10 mile final; had to re-engage both auto pilots and reset both master flight directors twice on the arrival. Prior to entering IMC; as briefed we switched to a heads up display arrival with increased minimums when the autoland autopilot system failed again. Shortly after that I received an approach warning in the heads up display; and with the approach lights [and] runway in sight; we completed the landing.The landing was on center line; but very firm. The taxi and shut down after that the normal. We wrote up the A3 automated system; and put it in the book. We debriefed the landing for the passengers and the crew.Maintenance is going to investigate the HUD; A3; and autopilot.

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.