When using speed intervene the MCP speed displays IAS instead of mach even above the mach/ias cross over level. In the 737 it 'knows' which to use; the 777 doesn't seem to. Is this correct?

I'd be very surprised if it didn't know whether it should be in IAS or Mach. Serious oversight if it doesn't IRL.

 

Best regards,

Robin.

I'd be very surprised if it didn't know whether it should be in IAS or Mach. Serious oversight if it doesn't IRL.

 

Best regards,

Robin.

 

Yes, it seems strange. If you get a chance would you mind confirming it's not just me?

I noticed that and found this in FCOMv2 p4.10.5. the last line says "In climb automatically changes from IAS to Mach at .84 Mach." and at the top of the next page "In descent automatically changes from Mach to IAS at 310 knots." 

When using speed intervene the MCP speed displays IAS instead of mach even above the mach/ias cross over level. In the 737 it 'knows' which to use; the 777 doesn't seem to. Is this correct?

Yes this is correct. I know it is strange but it is correct. During climb and descend the change is automatic, but in cruise the window opens with IAS, so speed intervention in cruise requires two button pushes. Speed intervention + ias/mach ref button.

Yes this is correct. I know it is strange but it is correct. During climb and descend the change is automatic, but in cruise the window opens with IAS, so speed intervention in cruise requires two button pushes. Speed intervention + ias/mach ref button.

Thank you!

 

A follow up question then: when required to fly a constant mach for instance when crossing the Atlantic, do you use intervene or mod speed on the crz page?

Since you know what Mach number and FL to fly well before entering oceanic airspace, you can enter it at the legs page.

 

At oceanic entry point type for example .84/360

At exit point type E/380 (westbound)

 

This way the FMC performance calculations (fuel remaining at destination) match your to be expected flight path. Also the airplane will fly Mach.84 automatically upon passing your oceanic entry point and revert beack to ECON at your exit point. You still have to start climb to FL360 and FL380 manually ofcourse (this is just entered for fuel estimate at destination).

 

Speed intervention would not be used.

If you dont want to enter the crossing speed in the Legs page for automatic speed change, then yes use the CRZ page.

Aha! I knew that you could enter a fixed speed on the legs page; I didn't know how to get it back to econ, so didn't use it. Excellent, thanks.

Once in a fixed Mach number you can also select ECON again from the CRZ page.

 

You are welcome.

Yes, IAS its correct. In the event of an emergency descent it is very useful to have IAS selected instead of Mach  :lol: