сортировка поля

$arSelect = array('ID', 'IBLOCK_ID', 'NAME', 'PROPERTY_*');
$arFilter = array(
	'IBLOCK_ID'         => $iblock_id,
	/*'ACTIVE_DATE'=>'Y',*/
	'ACTIVE'            => 'Y',
	'CHECK_PERMISSIONS' => 'Y',
	'MIN_PERMISSION'    => 'R',
	'PERMISSIONS_BY'    => $USER->GetID(),
);

$arSort = array(
	'PROPERTY_OBOROT_PLAN' => 'nulls,asc',
);



$res = \CIBlockElement::GetList($arSort, $arFilter, false, array(), $arSelect);
while ($ob = $res->GetNextElement()) { 
	$arFields = $ob->GetFields();  
	$arFields['PROPS'] = $ob->GetProperties();
	
	$arElements[] = $arFields;
}