Andrasz (#532) makes an interesting observation about the mismatch between the changing Russian rules and those likely to have applied to the Polish government flight. It scarcely bears repeating that if either the old Russian rules or the current western civilian concept of approach ban had applied the accident could not have happened because the approach could not have been flown. Provided of course the rules were adhered to.
But this does not really explain why the accident happened. The crew should have been able to conduct a PAR to limits and either land if suitable visual reference were obtained, or if not then go around. Conducted properly it would remain a safe operation, rules notwithstanding.
And if they were absolutely determined to land regardless by busting limits, surely the best chance of success would be obtained by scrupulously following the PAR down to DH/MDA then maintaining heading and descent rate towards the threshold.
It is clear this did not happen. The location of the wreckage and controller’s statements indicated the flight went well below the PAR glideslope and did not react to warnings and corrections. I find it hard to believe the crew would see any advantage from deliberately going so low so far from the runway and below the PAR DH, while hugely increasing the risk profile. What would be a likely DH - 300ft QFE perhaps? (We used to operate to 200ft in the UK many years ago. I imagine no-one on this forum can give us likely Russian data?)
I am not convinced that altimetry is the real issue. The PAR controller passes glideslope deviation advice and instruction derived from his own radar returns, rather than raw altitude. This is unlike SRA where the information passed is distance to touch down and an advisory altitude check for that point.
Ptkay’s point #539 about the terrain at Smolensk is worth noting and especially the Russian description of the “death trap”. But pilots are surely aware of the possibility of radio altimeter fluctuations on final approach at many airfields due to undulating terrain. It should be irrelevant to the conduct of the PAR, just as with ILS .
I have made the assumption that the approach was PAR because that is what the Russian statements appear to be saying and it would have been the most logical procedure in the circumstances . We need to know why the approach went wrong. Could they have been flying some alternative non-standard procedure (GPS ?) using PAR only for monitoring ?