Civilian aircraft on 11175 kHz USB, twice

[Token]

Heard something on the HF-GCS network today that I don't think I have heard before. Two different regularly scheduled United Airlines flight, at different times, requested a radio check on 11175 kHz, and both times got a response from West Coast.

At about 2218 UTC on April 15, 2023, United 1948 requested a radio check from Mainsail on 11175 kHz. "Mainsail, Mainsail, United 1948 radio check on 11175 kHz". This was sent twice, two different transmissions. The response after the second transmission was "Last caller, last caller, this is West Coast, West Coast, please say again last, over". From United 1948 "I've got you loud and clear, I was just trying a radio check, I might try one more frequency also". From West Coast "Lima Charlie on triple one seven five, over". From United 1948 "thank you for that".

A few seconds later, from United 1948, "West Coast, West Coast, United Nineteen-Fortyeight on triple one seventy five". Form West Coast "Last caller, last caller, this is West Coast, have you Lima Charlie, over". From United 1948 "United 1948 has you Lima Charlie, thank you very much for the checks".

Checking flight schedules, at that time United 1948 was en route and a couple of hours out from Cancun to San Francisco.

Shortly after this set of transmissions I heard United 1948 working San Fran on 11282 kHz USB.

At about 0042 UTC on April 16, 2023, about 2 and a half hours later, United 519 requested a radio check. This time I really could not make out much of United 519's traffic, but I heard all of the HF-GCS (West Coast) response. From West Coast "Last caller, last caller, this is West Coast, please say again last, over". From West Coast "United 519 this is West Coast, I have you Lima Charlie, over". A bit later, from West Coast "Last caller, last caller, I have you Lima Charlie, over". From West Coast "Untied 519 this is West Coast, I have you Lima Charlie, over".

Again checking the flight schedules, at that time United 519 was en route from Washington and a couple of hours out of San Francisco.

T!

[~SIGINT~]

I as well logged UNITED 519 at 00:37 UTC. My thoughts on this one is that the US military may have contracted out some civilian aircrafts to transport personnel.

160037Z APR 2023 11175.0 kHz USB
00:37Z UNITED 519 calling MAIN SAIL for radio check; response from WEST COAST;
00:39Z UNITED 519 calling MAIN SAIL for additional radio check; response from WEST COAST.

[Token]

I as well logged UNITED 519 at 00:37 UTC. My thoughts on this one is that the US military may have contracted out some civilian aircrafts to transport personnel.

That was my original thought also, but both flights are regularly scheduled daily's.  One out of Cancun to San Fran, one out of Washington DC to San Fran.

T!

[~SIGINT~]

My first thought was a retired USAF pilot using HFGCS to speak to someone / get a radio check but when you mentioned 2 seperate aircrafts then the gerbils started to spin.

[Token]

Same for me, I assumed, with the first one, some former USAF guy or current ANG guy, maybe showing his first officer what the HF-GCS was.  But the second one made that thought less likely. 

T!

[mike445]

United 1948 called mainsail on 11175 on the evening of the 16th as well.

[Token]

United 1948 called mainsail on 11175 on the evening of the 16th as well.

Got a time for that?

T!