Do simultaneous ILS signals cause interference?

[NeutronJ]

At GSO and IAH, both ends of certain runways use the same ILS frequency but with different identifiers. Wouldn't that cause interference if both were active at once? Or does ATC only activate the side in use? Are all ILS signals always on, 24/7, unless undergoing maintenance, or do they get turned on and off depending on traffic or weather needs?

 

[mrpotatohead]

Nope, both ends of a runway using the same ILS frequency wont cause interference because only one side is active at a time. ATC activates the ILS for the direction in use, while the other side remains off. ILS signals are not always on 24/7, theyre typically controlled based on operational needs, traffic, and weather conditions.

 

[NeutronJ]

That clears it up, I always assumed ILS signals were constantly broadcasting, so it's interesting to know they're selectively activated

 

[mrpotatohead]

Yeah, this happens because the localizer sends two slightly different frequencies and the aircraft's receiver compares them to figure out if it's to the left or right of the runway centerline.

 

[Roger that]

They're usually always on, but let's be real, sharing a frequency like that is a legacy design flaw. In today's airspace, it's borderline irresponsible and just waiting to bite someone in low visibility

 

[NeutronJ]

Yeah, this happens because the localizer sends two slightly different frequencies and the aircraft's receiver compares them to figure out if it's to the left or right of the runway centerline.

Right, but that's just how the signal guides you laterally, it doesn't explain the shared frequency issue. The real trick is that only one end's localizer is powered at a time to avoid interference.

They're usually always on, but let's be real, sharing a frequency like that is a legacy design flaw. In today's airspace, it's borderline irresponsible and just waiting to bite someone in low visibility

I totally agree, it's one of those "it works until it doesn't" setups. Feels like a holdover from a less complex airspace system, and someday it's gonna be the weak link in a chain