While on G/S the IAS on the EFIS comes back to life showing a value that varies and I can't figure out what determines it. Sometimes is very close to REF speed and some times not. I suppose it varies because my speed is not the same on all flights in "that" specific moment,  but what is that moment? is it a specific way point on my route, is it set on FMC (where) or is it a specific flap setting? 

thanks

 

While on G/S the IAS on the EFIS comes back to life showing a value that varies and I can't figure out what determines it. Sometimes is very close to REF speed and some times not. I suppose it varies because my speed is not the same on all flights in "that" specific moment,  but what is that moment? is it a specific way point on my route, is it set on FMC (where) or is it a specific flap setting? 

thanks

I do it when setting up for the brief. About 80 from the top of descent, I'll compare the PROG fuel to the current and then go to the REF page and enter that as my weight for landing. That gives me an accurate weight and Vref. Or you could just select the Vref without any correction. You'll be slightly faster than you need to be on final. It's normally workin a knot. No big deal.

Thank you for your reply but perhaps I didn't explain correctly. The problem is not how to enter the REF speed in APPROACH REF page, my problem is on the EFIS IAS/MACH speed indicator.

While cruising SPEED is not engaged (understandable since VNAV is) and as you are about to land comes back on automatically indicating a speed that can be anywhere between the REF and aprox. 200KIAS (i think depends how fast you go because varies all the time) and so my question is what causes the SPEED and the IAS/MACH to light up, is the distance from the T/C, is it the altitude or is it past a specific flap setting?  

When you capture G/S, AT switches to speed mode, setting the bug at current speed.

 

 

That gives me an accurate weight and Vref

 

Matt,

 

Or you could fly the AOA and always be correct. :smile:

 

blaustern

 

 

While on G/S the IAS on the EFIS comes back to life showing a value that varies and I can't figure out what determines it.

 

You use of the term EFIS is confusing.  You mean the MCP SPD value?  The NGX can fly the G/S with FMC SPD (VNAV) if you are deploying flaps on schedule and you have set desired speeds in the FMC that accomodate that schedule. I rarely use this but it does work.  There are usually a dozen reasons why the MCP SPD mode is used in the terminal area, but it's not because the NGX won't do otherwise.

Matt,

 

Or you could fly the AOA and always be correct. :smile:

 

blaustern

I was just in training and I heard we might turn those on. Expensive pixels.

 

 

Expensive pixels.

 

Yeah, all the code and hardware is already there I bet.  Features cost.

Those expensive pixels are worth every penny when you find yourself in an unreliable airspeed situation.

Those expensive pixels are worth every penny when you find yourself in an unreliable airspeed situation.

I think we've had Unreliable Airspeed for the last two years in training. It would be nice if we could get the best tool for the job.