Originally Posted by
threemiles
Mode-S in Central Europe interrogates MCP/FMS set altitude and QNH setting (FMS for Airbus, which is usually the origin or the destination)
The required equipment is mandatory for the Central Europe airspace.
However the resolution of the data transmitted is 100 feet.
So 13,008 or 96 feet is fake.
No, it isn't.
If, say, 13000 feet is the selected altitude at the time that parameter is interrogated, it can't be sent as that exact value because it's encoded as a 12-bit value where the LSB is 16 feet (MSB is 32768 feet, range is 0 to 65520 feet).
So 13,000 feet gets sent as the closest multiple of 16 feet, which is 13,008 (16 x 813) and 100 feet is sent as 96 (16 x 6).
It may well be that the controller's display rounds the value to multiples of 100 feet, but that's not what we're talking about here.
I see absolutely no reason to doubt those reported DAP Selected Altitude values, which are what you would expect to see as the FCU altitude knob is rotated over a period of some seconds.