Final check procedure
        The captain's name is John
        The pilot's name is Mary
        The mechanic's name is Mike
Traceback (most recent call last):
  File "exceptions#050.py", line 10, in personnel_check
    print("\tThe navigator's name is", crew[3])
IndexError: list index out of range

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "exceptions#050.py", line 19, in 
    personnel_check()
  File "exceptions#050.py", line 12, in personnel_check
    raise RocketNotReadyError('Crew is incomplete') from e
__main__.RocketNotReadyError: Crew is incomplete