It's done thousands of times every day. Not just the same airline, nearly all airlines are part of the CASS system, which authorizes this. There are multiple e

It's done thousands of times every day. Not just the same airline, nearly all airlines are part of the CASS system, which authorizes this. There are multiple examples of an additional crew member (an "off duty" pilot on the jumpseat is a crew member by the rules) being helpful in an emergency situation.