Gentlemen,
Greetings from Russia. Having had a privilege to know very well the captain of the SSJ who was really an outstanding pilot and personally a great man, I am very interested in every detail about this tragedy happened to my friend. And I am glad to read reasonable, professional and valuable comments here, with this forum.
I am not a pilot, but has been involved in various R&D projects in space and defence for more than 3 decades already, and would like to share some thoughts on an issue that likely was not yet raised here (sorry if I overlooked).
Putting aside the questing why they found themselves in the mountains, I assume that, while there, they relied to a certain (if not large) extent on the T2CAS (and here its TAWS part matters). As far as I can see in the publicly available publications, this system uses the digital terrain data, more precisely DTED (Digital Terrain Elevation Data) and some look-ahead algorithms.
So, I tried to figure out what digital maps are used in the civil aviation:
Terrain Awareness Warning System Databases for the Civil Aviation Industry
Here is the link to DTED for those not familiar:
DTED - Wikipedia, the free encyclopedia
And the question immediately arose about the DTED Level of the map available for this particular Salak region. It is well-known that interpolation errors on steep slopes can be huge. This article provides a good reference with quatitative estimates:
http://www.eurocontrol.int/sass/gall...%20DATA-11.pdf
E.g. in page 5 it is written that on a rough terrain in Alps, the elevation error for DTED Level 0 can be up to 307 meters (!!). For level 2 it was about 25 meters, and I assume that for Level 1 the error would be somewhat in between (and still high enough).
I would be happy to be mistaken, but it seems to me that Level 2 and higher (30 m post spacing and less) is not available for the Salak area. It would require too much effort to implement, while this area seems to be not much in use.
Thus, I would have a concern on performance of the TAWS on such a rough data, if it is of DTED Level 0 or 1. It's not a matter of avionics or onboard math, but if your input is that much «over-noised», your output would be hard to predict (e.g. the system may «shout» in a safe situation and keep silence or make a mild warning in danger).
What do you think?