Airlines that have now grounded the Boeing 737 MAX...

[brooklynite]

Ethiopian
Singapore
Aerolineas Argentina
GOL Linhas Aéreas
Cayman
Comair
Mongolian
Royal Air Maroc
China (all airlines)
Indonesia (all airlines)

No US carriers so far.

[USALiberal]

1. Either there's a problem with this plane or a really weird coincidence! nt

[still_one]

2. They have the black box. Hopefully, that will tell the story

[jmowreader]

3. They also have a go-team from the NTSB

[PJMcK]

4. There is a weird problem with this plane

Boeing changed the software that controls the stall prevention functions. However, if there are problems with the plane's external sensors, the software will override any flight commands made by the pilots. The result is a battle between the pilots and the software.

Boeing did notify the carriers using this plane but apparently the notices weren't forceful about the procedures to override the software.

Mentour Pilot, on YouTube, provides an excellent insight into the 737 Max and what the problems might be:

It's a bit lengthy but highly informative.

[brooklynite]

5. UPDATE: Additionals groundings

UK, Ireland and Germany ban all 737 MAX flights

[Stuart G]

6. Look at the countries and airlines that have grounded the 737 MAX. (or won't let them land)

These are listed in posts above...

Those airlines and some countries already believe there is a problem with this plane. Is caution the best way to prevent disaster? Exact same kind of crash in two places by these planes.

[spanone]

7. The U.K. has banned them from their airspace

sorry, missed your followup post.

[brooklynite]

8. Add Italy, Poland, Belgium, Netherlands