Instrument Landing Systems (ILS) on our runways assist aircraft during landings, especially in poor weather conditions. An ILS consists of two components: the localizer and the glide path. The localizer keeps the aircraft lined up with the runway during descent and the glide path provides a 3 degree descent profile for the aircraft to follow. Having a fully functioning and certified ILS is an integral part of maintaining safe airport operations.

There are five Instrument Landing Systems at YVR. The operation and maintenance of these systems is the responsibility of NAV Canada, the company responsible for providing air traffic control services in Canada.

Maintenance standards require each ILS to be checked four times a year. These checks include one 'annual' and three 'routine' checks, usually conducted on a quarterly basis. Additional checks may be required after maintenance or repairs.

A specially equipped NAV Canada Challenger 601 jet is used to check the systems. While performing the checks, the Challenger will fly a simulated runway approach, normally breaking off its approach once it is over the threshold of the runway. During the flight checks at YVR, this will often result in the Challenger flying over some residential areas at lower than usual altitudes, with the landing gear up. During a routine check, the Challenger will conduct up to 14 approaches to the runway being inspected and during an annual check it will conduct up to 28 approaches. These flight checks can result in some north runway departures.

Routine checks normally take up to two hours to complete, while annual checks normally take up to four hours. The annual flight check is followed by up to seven hours of post-flight checks by technicians on the ground, during which time the ILS for either end of the runway is out-of-service.

While the flight checks are normally scheduled months in advance, the exact dates of the checks will ultimately depend on weather and aircraft availability. ILS flight checks must be conducted in daylight with good visibility.

To ensure that the flight checks are done in a safe manner, they are typically conducted on Saturdays and Sundays - typically the days of the week with the lowest number of regular aircraft traffic at YVR. Flight checks normally start at 7:00 a.m. to limit conflict with other air traffic and to allow for enough time to perform critical post-flight-check work during daylight hours.