On Friday, United Airlines experienced a major computer systems outage which caused tens of thousands of passengers to be stranded with flights delayed or cancelled, including at San Francisco International Airport (SFO).

What do you do if you flight is delayed or cancelled?

The first rule of thumb is to try calling the airline's reservation desk. 

During major flight delays and cancellations, many airport customer service desks will have long lines.  Skip the line and call the airline's call center, whose phone agents typically have the same power as the airport agents.

If you can travel on a different day, then the airline can re-book you for another day free of charge.

If you would like to cancel your trip, the airline may be able to refund your ticket.

If you have to get to your destination as soon as possible, be persistent when talking with the agent.  Ask the agent if there are different routings and stopovers you can take to get to your destination.  If you know the airline's hubs, then specifically ask to be re-routed through the nearest hub which may have a connecting flight you need.

United Airline's domestic hubs include San Francisco, Los Angeles, Denver, Chicago (ORD), Washington D.C. (IAD), Houston, Cleveland, and Newark. 

If no confirmed flights are available, then you can ask to standby on a flight, which the airline will do for free during delays and cancellations.

However, be aware that the standby list is typically ordered by elite status and then time added to the list.  So if you don't have elite status with an airline, it's best to try to get a confirmed flight, since you may be way down on the list.

After confirming your new flight over the phone, go to gate agent for the new flight who should be able to print out your new boarding pass.

If you checked in bags, make sure to hold onto your baggage receipts.  Your bags may be routed on your original flight, and you will need those receipts in order to track your delayed luggage.