Practicable means possible.
Practical means taking account of all the circumstances and so as not to be too seriously inconvenienced. i.e. has a lesser imperative
Example: Last night BA137 LGW to FRE went tech 2 hours into the flight and returned to LGW. That was "practical" because it made sense.
If it had landed as soon as "practicable" it would be someplace 2 hrs down route now. Not very practical for BA.