Operational use of Primary and Secondary Channel

[Luca Simonini]

Hello, I am new to this forum, I am an engineer working for a project to support VHF comms for aircrafts. I would like to clarify the operational use of primary and secondary VHF channels. I understand that the primary channel is used for ATC, what is the usage of the secondary? Only as a backup?
Thanks to anyone willing to answer

[Roj approved]

In my company, and most I’ve flown in, 121.5 unless operationally required to be on another frequency. This would normally only be for Parallel runway Approaches, calls to the company/ground handlers, and in Australia, we have some airports without ATC, so then we use the 2nd VHF for the local traffic frequency (CTAF).

Hope that helps

[ShyTorque]

I use mine to tune into ATIS broadcasts or to contact a second enroute airfield where necessary. I’ve also used it to contact handling agents.

I would think most others do similar.

[Uplinker]

VHF 1 is usually used for "primary" communications with ATC. On many aircraft, the VHF 1 box is kept alive - for example by battery - when the aircraft electrical system is compromised. So it makes sense to use VHF 1 for primary ATC comms rather than having to switch boxes and frequencies in the event of electrical failure.

VHF 2 is used as a back-up for VHF 1 in the event of failure, and also for "house keeping" functions such as talking to handling agents, obtaining weather, talking to company operations, and in some cases - for example Gibralter - contacting the destination ATC to obtain approach clearance, while VHF 1 is tuned to an en-route ATC agency.

Thank you Denti, (below). I forgot to mention monitoring guard on VHF 2 Oops!

[Denti]

Pretty much the same around the industry i guess.

VHF 1 is for ATC, VHF 2 usually kept on guard listening watch, and can be used operationally for weather, ops and the like if those are not reachable via datalink. VHF 3 is on datalink and not usually used for voice comm.

[excrab]

Also in many parts of the world box 2 is needed for inflight broadcast procedures and negotiating entry at FIR boundaries, so ATC functions in addition to monitoring guard and house keeping stuff.