AJAX Yii textField

I am having problems when I want to update a textField. I am trying to implement ajax solution by modifying data on a textField, execute an operation and after show the result in impatto field.

View

<div class="row">
<?php echo $form->labelEx($model,'hhmm'); ?>
<?php echo $form->textField($model,'area',array(
                            'ajax' => array(
                                'type'=>'POST', 
                                'url'=>CController::createUrl('impala'),
                                'data'=>array('hhmm'=>'js:this.value'),
                                'beforeSend' => 'function(){
                                    var loading=$("<span>")
                                        .attr("class", "ui-autocomplete-       loading loading-remove")
                                        .html("&nbsp;&nbsp;&nbsp;&nbsp;")
                                        $("#Availability_impatto").after($(loading));
                                    }',
                                'success'=>'function(data){
                                    $("#Availability_impatto").empty();
                                    $("#Availability_impatto").append(data);
                                }',
                                'complete' => 'function(){
                                    $(".loading-remove").remove();
                                }',
                            )
                        )
                    );
?>
<?php echo $form->error($model,'hhmm'); ?>
</div>
<div class="row">
    <?php echo $form->labelEx($model,'percentuale'); ?>
    <?php echo $form->textField($model,'percentuale',array('size'=>4,'maxlenght'=>11)).' %';
?>
<?php echo $form->error($model,'percentuale'); ?>
</div>
<div id="impatto" class="row">
<?php echo $form->labelEx($model,'impatto'); ?>
<?php echo $form->textField('Availability[impatto]',
                    $model->impatto,
                    array('disabled'=>'disabled','rows'=>5,'cols'=>35,  'class'=>'ui-noborder fieldset-cyan')); 
?>
<?php echo $form->error($model,'impatto'); ?>
</div>

Controller

public function actionImpala() {

    $impalaval = UtilityHelper::impatur($this->hhmm,$this->percentuale);
    echo $impalaval;
    Yii::app()->end();
}