If you know somebody who works for an airline, you've probably heard them talking about their flight benefits. One of the perks of working for an airline is "free" travel to anywhere that carrier or its partners fly, but there are plenty of conditions. The most important point to clear up is that airline employees do pay for their travel (unless they're commuting for work) -- even though they may not be responsible for covering the airfare that you would normally pay to fly, they do have to pay certain taxes and fees.
These can total hundreds of dollars on an international itinerary, and while their total travel costs are lower most of the time, they hardly get to fly for free.
Despite the costs, airline employees traveling for pleasure are referred to as "non-revenue" passengers. In other words, the airline isn't making any money off of them, so they're prioritized below the lowest paying revenue passenger (including those traveling on award tickets). Most airline employees also fly standby, so they won't know if they're going to make it on a flight until after everyone else has made it on board. With unpopular routes, there shouldn't be any trouble, but if they're traveling on international flights to cities that the airline only serves once each day, and the flight is full, they'll have to try again tomorrow. And then the next day. And the day after that. If they have prepaid accommodations or tours, standby travel can actually end up being very costly.
The good news for employees is that any seat is up for grabs. If there's a First Class or Business Class seat that hasn't been sold, they may end up getting to sit there for the same "price" as traveling in Coach. Of course, there's no guarantee, and even passengers using upgrade certificates or miles to move up to the next cabin have a higher priority, so there's a fairly good chance employees will be riding in the back.
An airline employee's friends and extended family can travel on something called a buddy pass. Each employee is issued a limited number of passes throughout the year that they can use to book standby travel for people not usually covered by their flight privileges. These passengers are even lower on the standby list, however, and if the flight is just about full, there's a good chance they won't make it on board. Buddy pass passengers are usually only permitted to fly in Coach, but that's up to the individual airline to decide.
Free and buddy pass travel is a terrible idea during peak times, such as the Sunday after Thanksgiving, Christmas week or any time that there's inclement weather. If a flight is canceled, all of the displaced passengers will be accommodated on the next scheduled flight. If it's full, they'll end up on the standby list above non-revenue passengers. If a plane that holds 250 passengers isn't permitted to fly, that could mean 250 people ahead of you on the list, though that's an extreme example.
Non-revenue travel can be quite rewarding, but it's important to remember that you may end up not flying that day, or you could be stranded in a city that you weren't planning to visit.
If that happens, you're on the hook for meals and hotel rooms -- the airline won't help at all, so keep that in mind before asking a friend if they can help you fly for free.