Originally Posted by
KRviator
What makes you think the BlackHawk crew were on UHF, not VHF? Every military aircraft I've ever flown in - and there's been a few - speak to civilian controllers on civil VHF frequencies.
The VASaviation (and other) ATC clips have specifically mentioned that LC for KDCA transmitted back to the Helo on their separate assigned frequency, as well as the civil approach frequency. Basically dual transmit.
The audio is stitched back together.
But that's why nobody picked up the responses from the Helo crew, despite the LC clearly hearing and getting acks.
Complicating matters in that TRACON is that the military A/C also have their own controller on the assigned frequency. This is probably essential given the comings and goings at the Pentagon and local bases.
Given the track for the helo? It sure appears they expected the aircraft they were waiting on was lined up for 1, not 33. Given this, it is at least possible that they were watching the lights coming from the inbound AC from the Localizer for 1 (a A319 AA plane), not the CRJ descending through their position towards 33.
It's all conjecture, but the use of a separate frequency for the Pentagon-adjacent traffic is cited in several reputable reports as of this AM. Juan Brown's just uploaded an update with further information on the frequency split.
It seems clear from that the the CRJ likely could not hear the Blackhawk. And, with less certainty, that the Blackhawk probably didn't hear transmissions from the CRJ.