Can't hear aircraft at airport

[klunt]

Hi, this is not directly related to LiveATC, but is related to listening to ATC comms, so I hope that's OK. If not, mods can delete.
I was recently spotting at Wash Dulles (KIAD). I was on the top of a parking garage overlooking runway 1C/19C. I had my hand-held scanner tuned to the tower frequency for that runway. I could hear the tower clearly for every arrival and departure on that rwy, but could not hear any aircraft responses. Does anyone know why that might be? It can't be a distance/line of sight thing because I was within 1 mile of the runway threshold and had direct line of sight, but I heard nothing from any of the aircraft.

I use my scanner infrequently, but in the past, I've always been able to hear the aircraft when I'm in the vicinity of the airport.

Thanks

[Fryy/Avocadoflight]

It could be a combined frequency, or back up frequency where ATC transmits on both, but aircraft are on one. Try looking into all tower frequencies for that airport and scan all of them.

[klunt]

None of the resources I could find online listed any other tower frequencies for that runway, although other runways have different frequencies. Is there anything else that could explain it?

[AeroBill]

Listened to 120.250 for KIAD runways 1C/19L. Heard only the tower, no aircraft.
If you listen to 134.425 for runways 1L/1C/19R/19C you will hear same controller
and the aircraft.
So it looks like Tower is simulcasting on 120.250 and 134.425, but aircraft are
talking to Tower on 134.425. That would explain your question.

[tyketto]

Something that will also help. before tuning to the Tower frequency, tune to the ATIS to see not only the runways in use, but should also tell you if a tower frequency is combined on another frequency.

For example, at Las Vegas, the tower frequency runways 1L/1R/19L/19R is 118.75, while the frequency for runways 7R/7L/25L/25R is 119.90. Most of the time at night, they'll combine all runways to use 119.90 (depending on runway configuration). The ATIS will notify everyone regarding that. So get that info first before settling in, as you'll know what you need to tune your scanner to prior to settling in.

BL.