In simple english
Hi Hubert:
In simple english - the answers to some of your questions are as follows:
How come that pilot didn't know his alltitiude ?
There are two types of altimeters in a cockpit. The accuracy of the pressure altimeter depends on the air pressure given to the pilot by the controller. Assuming this pressure reading is correctly given by the controller and understood and set correctly into the altimeter by the pilot, he will always know the correct altitude he is flying. ( Bar a technical malfuction of course).
The radio altimeter is independent of any pressure readings and measures height above terrain. But I am sure you already see a problem with this during this particular approach. Even though the plane may be flying level, if the configuration of the terrain underneeth changes, so does the reading on the radio altimeter.
Optical illusion mentioned before is probably not the case in poor visibility ?
I saw that someone already gave an excellent explantion for this so no need to dwell on that.
Why control tower didn't warn the crew that they are too low ?
According to most reports, the controller did warn the crew but received no response. Again we will not know if that was the case until CVR transcripts are availabe.
Regarding post crash response - sorry, can't help you there as I simply did not research that aspect of the story.
By the way, I am Polish too even though I have been " on the other side of the pond" for 20 years and it is here that I learned to fly. RIP to all our countryman and woman that lost their lives.