Hi all!

I know you can display the FPA of choice on the HGS via its control panel and that you can select the required FPA in the DEP/ARR page of the MCP if no specific approach is selected for a rwy but I was just wondering, is there a way to select it via the MCP as an alternative to VS?

 

Also, can somebody more knowledgeable than me explain the difference in between a slope expressed in º and as a % and how to convert it?

Thankyou!

First part, no idea! Second part:

 

If we take a typical glide path for an aircraft:

 

 

This slope can be expressed in three main ways:

1) 1:20 (1 in 20) this tells us for every unit up(or down) we will travel 20 units left (or right). Generally expressed as y:x, where y is the vertical distance and x is the horizontal distance.

 

2)As a percentage:

1/20=0.05

0.05x100=5%

 

3)As an angle:

So, we want to know angle a, the angle from the horizontal at which the aircraft will fly. Through the alternate angle rule, a=b. To work out angle b, we can use some right angle trig:

 

tan(b)=opposite/hypotenuse

hence: inverse tan(opposite/hypotenuse)=b

inverse tan(1/20)=2.86 degrees

because b=a, a=2.86 degrees

 

As for converting between, draw a small triangle and fill in the values you know(eg. the angle) then substitute 1 into the horizontal component and resolve for the vertical component. Then divide the vertical by the horizontal and multiply by 100 to get the percentage.

 

I hope this helps!

It does thanks, very well explained. That's all clear now thank you!

Anybody else got an idea about the first question?

You can fly a runway extension in LNAV/VNAV. No need for any special modes.

Yup but what about if it's not a straight in landing but I'm still required a prescribed fpa (eg am offset approach?

Yup but what about if it's not a straight in landing but I'm still required a prescribed fpa (eg am offset approach?

 

You can still fly VNAV down to MDA or use V/S from tables in approach charts.

Ok, does this mean there is no way to imput the fpa in the mcp?

That's exactly what it means... It's not an Airbus, you know ;-)

It's not an Airbus, you know ;-)

 

You can do that on triple seven, E-jets and maybe some other also.

Did not know that, although it is pretty logical in retrospect.

Thanks!