I used the phrase, the mike not keyed in another post and it reminds me of something else for unsettling your memory. While other permutations may have applied elsewhere, any of the headsets I used (Plantronics MS50 or Starset) were available with two different kind of PTT (push-to-talk) switches in the hand piece—locking or non-locking. At one time or another I have had both, but discovered soon enough that I much preferred the non-locking, as it was impossible to inadvertently lock it in the keyed position.
But what comes to mind in this discussion is occasional remarks I’ve seen on the web of controllers taping their mic button down for a serious session. For non-controllers reading this who might not know, controller communications are almost 100% call and respond. In other words, I issue a clearance and then wait for a reply. In fact, the reply is vitally important in almost all of our communications, and there is no place for a locked on transmitter in them.
Except…during my tour at ORD I got to spend some time in the tower getting familiar with operations in the cab and how they related to the job I was learning down in the TRACON. Same story, call and respond, except Outbound Ground. The procedure was for flight crews to call Clearance Delivery for their airways clearance (route of flight, initial altitude, transponder code) and a request to call Clearance when ready to taxi. Later configurations had the flights contact Pre-Taxi when ready.
When the aircraft was ready to taxi CD would take the strip belonging to the flight and place it on top of the stack the Outbound Ground had in front of him and the flight was advised to “monitor Ground on point 75” (aviation shorthand for 121.75). Not “contact”, but “monitor”. The Ground Controller, with a dozen or more strips in front of him had been issuing taxi instructions for a while, had his mic locked on, and contiuously read the specific taxi instructions for each flight, placing the strip on the appropriate Local Controller’s bay, and then moving on to the next clearance. There was a lot to know about the airport operation at Outbound Ground, and all the insiders knew that it was the toughest position in the cab. Once you’d checked out on Outbound, you were excused if you felt confident you were going to make it.
One final example, I believe even GCA/PAR controllers let up the PTT periodically during their operations. Even though they transmitted an instruction every few seconds, there was no reason to keep the mic keyed. In their instructions before beginning the approach, they would advise, “do not acknowledge any further transmissions If no transmissions received for five seconds, execute missed approach and contact…(facility)”. That pretty much implies there will be breaks in the transmission stream, although no response is expected. But, although I did a surveilance approach or two at ORD, that’s not a PAR, at which I have no experience.
The coda to this Ground Control discussion is that there was no acknowledgement possible by the aircraft and part of their taxi clearance included the instruction to “monitor the tower (Local) frequency when nearing the runway. The Local controller would similarly instruct flights to “follow the tri-jet” or whatever, but since Local is the very definition of call-and-respond, never locked his mic on.
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