I was under the impression that Ada is significantly safer than C++, particularly with the 2012 standard that adds support for contracts, and that it mainly suffers from a lack of tooling.
The elephant in the room there is the importance of tooling. Consider, explosions and explosive chemicals are themselves ridiculously dangerous and for the most part to be avoided. However, with the proper tooling and use, one can use them to accomplish some fairly amazing things.
That is, many of the "safer" languages try to get by with disallowing explosive and dangerous constructs. With some of the more advanced tooling that is available and good discipline, one can still do some amazing things with them.
My knowledge of safety critical software is not extensive and several years out of date, but my understanding is that the big two languages in safety critical software are still MISRA C (a subset of C designed to enforce safety via static analysis, see http://en.wikipedia.org/wiki/MISRA_C), and Ada.
As far as I'm aware, Fortran and Algol are not widely used. But feel free to correct me.