And please answer my questions about the transponder without bypassing the subject.
I am not familiar with the Legacy aircraft but most aircraft are the same.
If the transpnder fails, you will get a warning, but it is VERY easily missed.
If you turn off the transponder, then there will be no warning.
There is speculation that the crew accidently turned off the transponder.
This is not the cause of the accident. Aircraft experience transponder malfunctions every day. Some of these malfunctions are simple "finger problems".