probelm when acquiring information about events

ERROR 2017-09-22 14:47:44,973 exception 20219 140265719699200 Internal Server Error: /api/events/2017-09-25/
Traceback (most recent call last):
  File "/var/www/scheduling-system/env/local/lib/python2.7/site-packages/django/core/handlers/exception.py", line 42, in inner
    response = get_response(request)
  File "/var/www/scheduling-system/env/local/lib/python2.7/site-packages/django/core/handlers/base.py", line 187, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/var/www/scheduling-system/env/local/lib/python2.7/site-packages/django/core/handlers/base.py", line 185, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/var/www/scheduling-system/env/local/lib/python2.7/site-packages/django/contrib/auth/decorators.py", line 23, in _wrapped_view
    return view_func(request, *args, **kwargs)
  File "/var/www/scheduling-system/smash/web/api_views/daily_planning.py", line 215, in events
    'flying_team_location': str(appointment.flying_team),
UnicodeEncodeError: 'ascii' codec can't encode character u'\xfc' in position 7: ordinal not in range(128)