FAA re-validates RDU airport approach systems
Planes heading to RDU are a common sight in the skies above the Triangle, following the same path through the sky, especially within a few miles of the airport.
Have you ever wondered how pilots find and follow that path every time, or how aircraft can safely land in less than ideal weather conditions?
The Instrument Landing System (ILS), a series of radio transmitters, paints an electronic path through the sky enabling pilots to bring their aircraft in on the perfect glide slope, right onto the center of the runway, even in the worst of weather.
How ILS works
When the weather is good, pilots can use the Precision Approach Path Indicators (PAPI), a set of highly directional, very bright red and white lights positioned at the side of the runway. PAPI lights can be seen 3 miles away in the daylight, 20 miles at night and are aimed in a way that tells pilots if they are to high (“all white, check your height”), on correct glide slope (“red on white, I’m alright”), or too low (“red on red, you’re dead”).
Space Shuttle pilots used a similar PAPI system to judge approaches the Kennedy Space Center, but instead of the comfortable, shallow 3º glide slope in use at nearly all airports (including RDU), shuttle pilots dove the 86 ton orbiter at a dizzying 20º.
They would have used the PAPI systems at the Wilmington International Airport or Marine Corps Air Station Cherry Point. Both were identified by NASA as emergency landing locations should two or more of the shuttle's main engines fail during launch.
ILS also sends out highly directional eletromagnetic energy, but uses radio waves instead of light. ILS sends out verical beams to identify the glideslope but also sends out horizontal beams to help pilots line up perfectly with the runway
The ILS localizer is an array of antennae that transmits two narrow beams from the end of the runway which intersect right over the centerline. Listen to the tower chatter, especially at RDU's observation park, and you'll hear tower controllers guiding pilots to "intercept the localizer". This puts them on the correct 54º heading to runway 5L (runways are named with the last digit dropped, with L or R for parallel runways such as RDU's).
The ILS glideslope (ILS GS) similarly transmits a pair of narrow intersecting beams, one slightly above that required 3º path into the airport, one slightly below.
The intersection of these two systems is the path you see aircraft following each day into the airport.
Residents of southwestern Wake county may have noticed an aircraft flying back and forth between southern Durham and Cary. Tammy Jones of the FAA confirmed that this aircraft, part of the agency's Flight Inspection Operations group, was performing flight checks following recent maintenance of RDU's ILS.
The flight pattern took the aircraft along an arc where aircraft "intercept the localizer".
FAA’s Flight Inspection Operations group flies several types of aircraft to validate the systems that help pilots safely land at more than 5,500 facilities world wide, including RDU. Flight checks like this one measure the accuracy of systems as well as human factors to ensure the “flyability” of procedures.
It's all about keeping the airport and skies above it safe.
