B737-400 Mcp

[comfortably numb]

Can someone answer this please.

When in cruise what is displayed in the speed window on the MCP.............and..................is it possible to change the cruise Mach number through "speed" selection.

Last but not least.............what does the C/O button do ?

[Romeo E.T.]

what is displayed in the speed window on the MCP

your current airspeed in knots, or as a mach number, or it is blank when in VNAV profile, then the FMS determines the speed.

is it possible to change the cruise Mach number through "speed" selection.

yes

what does the C/O button do

indicated airspeed/Mach number

[comfortably numb]

Ok so with VNAV in control the mach is updated on the cruise page.

but if its not ie just in LNAV then the c/o will toggle IAS/Mach and i can fly different mach ( for ATC say ) by changing the speed selection....

Its all flooding back now.

[ImbracableCrunk]

You can either change it in the FMC (FMC SPD) or you can open the speed window with speed intervention and manually select it (MCP SPD).

[comfortably numb]

What is speed intevention ? I used to fly the damn things............but for the life of me I cant remember any other other way of changing our Mach other than ..as you say through the FMC

Is that what the C/O button does ?

we were not allowed to touch anything once the wheels were up

[d105]

Speed intervention allows for MCP control of the speed while the FMC remains engaged in VNAV. It has basically the same function as LVL CHG.

Personally I only use the intervention in two situations.

1. When doing a VNAV idle descent and I'm messing around in the FMC with cruise altitudes, altitude restrictions or speed limits. Basically anything that can have an impact on the FMC commanded speed in VNAV. When using speed intervene, the A/P holds the select mach or IAS. So i can execute in the FMC without worrying that the AP will suddenly dive like crazy or go into energy conservation mode.

2. For speed control while flying a VNAV approach. The intervene function will only allow for actually speed control when in the approach segment of the coded approach or when you have flaps out (VNAV PTH). Otherwise it will go into retard idle descent. (VNAV SPEED).

If you have flaps out it will go into VNAV PTH with manual speed control via the speed intervention window 100% of the time. Without flaps selected, it's hit or miss depending on the programmed approach. I've asked a few people at what distance along the approach the FMC will actually transition into VNAV PTH and nobody knows for sure. I've seen it happen at around 10nm LNAV track, but sometimes already at 15 or later. Someone care to explain why?

[BOAC]

What is speed intevention ? - it is simple - press 'SPEED'

[Denti]

- it is simple - press 'SPEED'

Not really, there is a dedicated Speed Intervention button, same as there is an ALT Intervention button.

But as d105 mentioned above it is rarely used. VNAV approaches are nowadays flown in approach mode and therefore allready have an open speed window without any need of speed intervention.

[ImbracableCrunk]

What is speed intevention ? I used to fly the damn things............but for the life of me I cant remember any other other way of changing our Mach other than ..as you say through the FMCSome companies didn't pay for all the MCP options. Some bought none or only speed intervention, some got both speed intervention and alt intervention. If you don't remember using them, that could be why.

[Nightrider]

Denti, you are obviously one of the lucky colleagues where the company paid for some extra bits and pieces. Most of the "classics" do not have any of the intervention buttons at all...nicely covered by a matching piece of plastic hides the button place...:oh:

[BOAC]

Absolutely, NR - unlike the obviously heavily spoilt and much pampered Denti, the rest of us probably unscrewed the plastic covers on a long boring sector to find...........................by which time the 'need for speed' had long passed. :D