Custom attribulte value is not storing to order_attribute table of Magento

Question

I have created one module for storing custom checkout field value in sales_flat_order custom filed. the filed is created. but the value it not storing after place order. I am new in Magento.

app/code/local/Iclp/Orderattribute/etc/config.xml
<?xml version="1.0"?>
<config>
  <modules>
    <Iclp_Orderattribute>
      <version>0.1.0</version>
    </Iclp_Orderattribute>
  </modules>
  <global>
    <helpers>
      <orderattribute>
        <class>Iclp_Orderattribute_Helper</class>
      </orderattribute>
    </helpers>
    <models>
      <orderattribute>
        <class>Iclp_Orderattribute_Model</class>
        <resourceModel>orderattribute_mysql4</resourceModel>
      </orderattribute>
    </models>
    <resources>
      <salesattribute1422420996_setup>
        <setup>
          <module>Iclp_Orderattribute</module>
          <class>Mage_Sales_Model_Mysql4_Setup</class>
        </setup>
        <connection>
          <use>core_setup</use>
        </connection>
      </salesattribute1422420996_setup>
      <salesattribute1422420996_write>
        <connection>
          <use>core_write</use>
        </connection>
      </salesattribute1422420996_write>
      <salesattribute1422420996_read>
        <connection>
          <use>core_read</use>
        </connection>
      </salesattribute1422420996_read>
    </resources>
    <events>
      <checkout_type_onepage_save_order> <!-- identifier of the event we want to catch -->
        <observers>
          <checkout_type_onepage_save_order_handler> <!-- identifier of the event handler -->
            <type>model</type> <!-- class method call type; valid are model, object and singleton -->
            <class>orderattribute/observer</class> <!-- observers class alias -->
            <method>getorderattribute</method>  <!-- observer's method to be called -->
            <args></args> <!-- additional arguments passed to observer -->
          </checkout_type_onepage_save_order_handler>
        </observers>
      </checkout_type_onepage_save_order>
    </events>
  </global>
</config> 
app/code/local/Iclp/Orderattribute/Model/Observer.php

<?php
class Iclp_Orderattribute_Model_Observer
{

            public function getorderattribute(Varien_Event_Observer $observer)
            {

        $event = $observer->getEvent();
        $order = $event->getOrder();
        $fieldVal = Mage::app()->getFrontController()->getRequest()->getParams();

        $order->setOrder_Attribute($fieldVal['order_attribute']);
        //echo "<script>alert('fff');</script>" ;
            }

}


sql/salesattribute1422420996_setup/mysql4-install-0.1.0.php

<?php
$installer = $this;
$installer->startSetup();
$installer->addAttribute("order", "order_attribute", array("type"=>"varchar"));
$installer->endSetup();

Answer 1

I think there is misconfiguration in your module.

<global>
...
    <fieldsets>
        <sales_convert_quote>
            <your_special_attribute>
                <to_order>*</to_order>
            </your_special_attribute>
        </sales_convert_quote>
    </fieldsets>
...
</global>

Have you assign new attribute to qoute?

$installer->addAttribute("quote", "order_attribute", array("type"=>"varchar"));