i checked the wiki and find that:
"Fail-passive autopilot: in case of failure, the aircraft stays in a controllable position and the pilot can take control of it to go around or finish landing. It is usually a dual-channel system.
Fail-operational autopilot: in case of a failure below alert height, the approach, flare and landing can still be completed automatically. It is usually a triple-channel system or dual-dual system."
737-800 autoland is a dual channel system, so it doesn`t look like a fail-operational autopilot.
maybe as PEI said ,
limitation for tailwinds greater than 10 knots reflects the capability of the airplane as evaluated in terms of airworthiness but does not constitute approval for operation in tailwinds exceeding 10 knots". thank you all, i kind of sort this thing out~
but i still need to verify with my company~
great appreciation!