Musicrab writes:

What's the Boeing 737-800 flight manual say about what to do when left and
right hand altimeters don't match?

It surely points out that working altimeters are required for an automated
approach. The airline flew with broken altimeters, and after tempting fate
several times, it finally caught up with them.

Turkish Airlines has the worst safety record of all airlines in Europe and the
U.S. combined, in terms of flights with fatalities over total flights. And it
trails by quite a margin.