737 NG Communication MIC selectors

[Driver 170]

Reading my FCOM 2 and on the pedestal you have SERV INT and FLT INT. How are these actually used by pilots? Do you select FLT INT when speaking to ground for example?

I watched a Ryanair preflight video that i got sent and the Capt had the MIC SEL on VHF 1 all the time when talking to the ground? How is that possible i thought you would have to select FLT or SERV INT?

Be great if someone could clear it all up for me.

Thanks.

[Tom!]

There is a two position switch on the control column. One side keys the selected radio,vhf1 usually, other side always flt regardless so no need to select it. Or the hot latch was on on the ACP. No need to press any buttons then if you want to talk to ground.

[Driver 170]

So on the control wheel you have R/T and that transmits whichever the MIC sel is on and the I/C transmits over the Flight intercom? So is the FLT INT always used for the ground then?

What is HOT mike usage??

The SOP for Hotmike usage is:
 I/C selected ON after pushback and prior to obtaining taxi clearance.
 I/C shall remain ON until completion of the TEN Checks Climbing, after which
it will remain crew discretion to either turn the I/C ON or OFF.
 I/C shall be on prior to the Descent checks and remains ON for the remainder
of the flight until the Parking Brake is set at the stand, then OFF.

[Driver 170]

So if you can transmit on FLT INT with the control wheel I/C why have the FLT INT on the ACP ?

[Chesty Morgan]

The intercom switch on the column is not transmitting per se. It's essentially a switched hot mic, the same as the switch on the ACP. If that fails you can select flight interphone on the ACP and "transmit" using either transmit switch to ensure you can still speak to your oppo.

Also if you have a stuck mic you can select flight int. to prevent transmitting on VHF or HF.

You generally speak to ground via the intercom switch on the column.

Do whatever you want with the hot mic, most people just turn it off and on as required. However, if you leave it on I don't want to hear stereophonic chewing sounds. I will eject you. ;)

[Driver 170]

So why is it called a hot mike?

[Wirbelsturm]

It's permanently on transmit so you can chat to your mucker over the intercom without having to press the transmit button for the intercom all the time.

Pain when some one leaves it on 'hot' and sneezes though!

For the bigger Boeings latch the switch on the yoke down for intercom hot mike. Not sure about the 737.

[Driver 170]

So how can you actually turn off HOT MIKE usage? So hot mike is basically like a mobile phone speaking to each other without pressing the Inter comm

[Chesty Morgan]

For the bigger Boeings latch the switch on the yoke down for intercom hot mike. Not sure about the 737.

The same.

170, Tom's post has lead you astray because the control column switch is three position. Middle is off, up is transmit and down is intercom (hot mic).

[Driver 170]

Is the control column latched in?

[Wirbelsturm]

Only the 'down' intercom position is latched, you need to 'pull' the switch up to return to the mid-point. Radio transmit, i.e. pulling the 'top' toward you, is spring loaded back to the mid position.

[Jwscud]

Not on the NGs. The intercom is latched to I/C using the switch on the onside ACP. The PTT on the yoke doesn't latch in either position so one can use it to speak to either without disturbing your intercom switch. For pushback, the ground crew plug into Flight Interphone on the panel below the FOs window.

It is good manners to use the R/T side of the ACP switch to avoid gripping the yoke when your colleague is hand flying, especially when it is getting windy. The "death grip transmit" is a pet hate of mine!

[Chesty Morgan]

Not on any of the NGs I fly.

The control column switch latches down for hot mic. The switch on the ACP is spring loaded in both directions.

[Wirbelsturm]

Sorry, didn't clarify, I was talking about the yoke switch on the 777, the ACP switch is, indeed, sprung loaded both ways.

Often when there is an audible hiss in the background the source will be an intercom switch left down on one of the yokes.

As stated above I know nothing about the 737. :D

[Simtech]

Being pedantic, I should point out that there are in fact two separate switches in the yoke of a 737 (including the NG); one for radio PTT, the other for intercom. They are activated by a rocker mechanism, top in is radio transmit, bottom in is intercom, centre position is off. The intercom position is latched by a spring-loaded ball set in to the botton of the rocker - this engages with a L-shaped metal bracket to hold the switch in position.

As I understand it, the latching intercom switch is a CAA requirement for UK-registered aircraft but (as always) I'm willing to be corrected.

[Jwscud]

On the EI registered bunch I fly, the yoke switch doesn't latch at all. The ACP switch latches in IC and is spring loaded to off.

It is the ACP switch that is used to latch the intercom after start.

Good old EASA - unity through difference...

[Driver 170]

I watched a Norwegian 737 NG to Svalbard and the FO was pressing the MIC on the Glareshield is that basically VHF 1 and using R/T ?

[Simtech]

I don't remember seeing a 737 of any series with a Mic (I presume you mean PTT) button on the glareshield - only on the yokes and the ACPs. Glareshield carries the AFCS MCP, two EFIS selector panels and two warning/caution displays.

[Driver 170]

Strange, just whenever he was transmitting something back to ATC he was pressing a button the glare. Maybe it was something else!

[Chesty Morgan]

We have a couple of NGs with the glareshield transmit button. Does exactly the same as either of the other two transmit switches - so it'll transmit on whatever is selected on the ACP.

[Wirbelsturm]

The 777 has a glareshield PTT next to the clock button. I 'believe' it was an option for the 737.

Happy to be corrected though.

You have 4 options on the 777, the yoke transmit, ACP transmit, glareshield PTT and the standby mike.

Perhaps some of the newer NG's follow that layout?

[Chesty Morgan]

Most of ours aren't particularly new.

Most haven't got the clock button on the glareshield. Some have, some have PTT only, most have neither and some have both - which is fun because you can see how long it takes you to realise you didn't actually transmit.

I don't think any have the standby mic.

Must've been a customer option.

[Denti]

We had a couple 737s with the clock button on the glareshield right next to the PTT switch (both looked and operated the same...). The company didn't like it and now its just the PTT switch on the glareshield. The glareshield button had to be introduced once the latch option was selected for the yoke button which in turn was required once the worker safety and health regulations required an ANR in the 737 because of the deafening noise on the flightdeck, unlike the airbii which are silent enough so that we don't require ANR headsets.

Transmit options are the ACP switch, yoke (latches in IC), glareshield PTT and the hand mike. Some older ones still have a handset for cabin intercom and PA although all those options are available via the ACP as well.