ATC gave command to descend to DH of 50 meters. CAT 1 DH is what with a precision approach?
Make that height not altitude.
A typical Cat I DH is 200 feet AGL, but that has nothing to do with this case.
Pilot was not “cleared” to descend below whatever the DH or MDA was for the approach he was using. These MINIMUMS are exactly that, they are MINIMUMS below which he was not authorized to fly unless he had a clear view of the “runway environment” in view, (in other words, unless he had a clear view of the runway by looking out the window.)
These minimums do NOT come from ATC via radio. They are published on small charts, one for each type of approach to each runway, called Approach Plates. ATC cannot lower those minimums.
Here is a sample approach plate.
http://tiles.skyvector.com/sky/files/tpp/1008/pdf/00257IL9.PDF
It is for an ILS to Runway 9 at MIA, Miami International Airport. At the top of the Plate you can see that the TDZE is 7. That means that the touchdown zone of the runway is 7 feet above sea level.
Look at the bottom of the plate. You'll see the notation for the ILS “207/24 200(200-1/2)” That means that the DH for that approach to that runway is 207 feet above sea level on the barometric altimeter, or 200 feet above the 7 foot TDZE (200 feet above the ground.)
This is all meaningless in the Smolensk accident, however, because the aircraft was flying over (and crashed into) a ravine at an altitude of 15 feet BELOW the TDZE for the runway in question.
It's all rather simple, really.
The former Sovs can be bad boys, but despite what some Polish tabloid claims, this error was caused by pilot error, not the Russians.
There was no ILS at Smolensk. Only NBDs. A typical MDA would have been at least 500 feet above the TDZE. The pilot was 15 feet BELOW the TDZE.
In addition, the flight data recorder voice channels have multiple recordings of the automated voice driven by the radar altimeter loudly announcing “Low - Pull Up!” and “Terrain Ahead!” That automated voice is quite loud and unmistakable.
That has been confirmed by Polish investigators.
A good sim of the crash is shown at http://wyborcza.pl/1,75478,7761110,Tak_doszlo_do_tragedii.html
Notice that it was his 4th approach. The Commanding General of the Polish Air Force in the cockpit telling the pilot that he “had better find a way to land.”
A perfect recipe for a disaster.