cakephp is not associated with model

I am in trouble in cakephp.

Model: agent.php

class Agent extends AppModel{
    var $name = 'Agent';

    var $belongsTo = array(
    'Arrival'=>array(
        'className'=>'AirTime',
        'foreignKey'=>'arrival_id'
    ),
    'Departure'=>array(
        'className'=>'AirTime',
        'foreignKey'=>'departure_id'
    ));
}

Model: airtime.php

class AirTime extends AppModel{
    var $name = 'AirTime';
}

Controller: agentController.php

        $condition = array(
            'limit'=>20,
            'contain'=>array(
                'Arrival'=>array(
                    'fields'=>array('airline_id','flight_num'),
                    'Airline'=>array('fields'=>'code')
                ),
                'Departure'=>array(
                    'fields'=>array('airline_id','flight_num'),
                    'Airline'=>array('fields'=>'code')
                )
            )
        );

        $this->Agent = ClassRegistry::init('Agent');
        $this->paginate=$condition;
        $data = $this->paginate('Agent');

When you run the source of, Warning error is output.

Error:

Warning (512): Model "Agent" is not associated with model "Arrival" [CORE/cake/libs/model/behaviors/containable.php, line 343]
Warning (512): Model "Agent" is not associated with model "Departure" [CORE/cake/libs/model/behaviors/containable.php, line 343]

I do not know how to solve this problem.