The link below has a sample 21 day extension to file a Brief with the EOIR/BIA Executive office of Immigration Review Board of Immigration Appeals. The BIA has issued instructions that they will not grant extensions as a matter of course as they were doing in the past. We have started to see some extension request rejected. It is prudent to add as much information as possible as to your reason for needing an extension. This is a sample only and you should be an attorney or consult an attorney before using it.
Download Here. Google Docs