Interline travel (or offline travel) refers to airline employee discounts for travel on other airlines. Interline travel benefits are often available for employees, spouse, parents, dependent children and retirees of the airlines.
Interline benefits are often negotiated by an airline's "pass bureau" (in America) department or can be obtained by using independent companies The applicable fares are called ZED (Zonal Employee Discount) fares. Prices are mileage-based or based on city pairs.
The ZED program was designed to be simpler than the old system of ID discounts (ID90, ID50, etc.) which was based on a percentage discount off the published full fare (either coach or first class) for a route given a specific origin and destination for each ticket.
Interline travel discounts on other travel industry suppliers varies by supplier and travel time. Interline discounts on cruises and hotels can be booked through interline travel agencies. To qualify the traveler must provide proof of eligibility, such as a copy of their airline ID badge or letter of employment on airline letterhead. A handful of fully qualified interline travel agencies, mostly in North America, provide interline services.
Some interline agencies also offer travel discounts for active and retired military.
Usually employees of defunct airlines, (Ozark Airlines, Braniff Airlines, Midway Airlines, etc.) do not qualify for discounts. The exception is typically TWA, which merged with American Airlines before they went out of business.
Interline discounts are typically offered close to departure dates, however some vendors (hotels) offer them as much as a year in advance.
Interline travel often involves flying Standby traveling only if unsold seats remain. For this reason this benefit has become less valuable as more flights run full. Usually off-duty crew can use free jump seats either in the cabin or the cockpit should all passenger seats be taken.
E-ticketing for interline travel is now supported by several carriers.