message: action_impl: debug output if arming is not allowed
diff: @@ -189,6 +189,7 @@ void ActionImpl::return_to_land_async(const Action::result_callback_t &callback)
  bool ActionImpl::is_arm_allowed() const
  {
  if (!_in_air_state_known) {
  + Debug() << "landed state not known, arming not allowed";
  return false;
  }
  