SharePoint: Reorder fields in content type

Here is a PowerShell script to re-order fields in a List Content Type:

$web = Get-SPWeb http://aissp2013/sites/TestSite
$list = $web.Lists["MyList"]
$contentType = $list.ContentTypes | where {$_.Name eq "MyTestCT"}
$ctFields = "Title","ColumnA","ColumnB","ColumnD","ColumnC"
$contentType.FieldLinks.Reorder($ctFields)
$contentType.Update()