FMC offset route

[Hardy Heinlin]

By the way, does anybody know where the green E/D donut for the E/O drift down target sits when a route offset is in use? Is it on the normal route or on the dashed offset route?




Edit: Thread split from http://aerowinx.com/board/index.php?topic=4799.0

[emerydc8]

By the way, does anybody know where the green E/D donut for the E/O drift down target sits when a route offset is in use? Is it on the normal route or on the dashed offset route?

Hi Hardy,

I don't know if I have a definite answer for you on this, but I did learn something this morning that I didn't know and didn't think would work. I set up a 15-mile right offset prior to T/D to see if the T/D point would be displayed on the original course or the offset course. To our surprise, the dot was displayed on the offset course. You can make your own assumptions about this, but if it does it on the 767 for a normal descent, I'm thinking it would also display the E/O points on the offset route too.

[Hardy Heinlin]

Hi Jon and all,

re offset route again: When an offset route is active, do you know what the x-track error display on the PROGRESS page refers to? To the normal route or to the offset route? E.g. when the aircraft is on the dashed offset route and the offset is 20 nm, will the PROGRESS page indicate 20 or 0 nm?

In the current PSX version, the display always refers to the normal route.


|-|ardy

[emerydc8]

Hi Hardy,

I fly tonight. I'll check it out if I can.

Jon

[Hardy Heinlin]

Thanks! By the way, to check this out, you don't even need to fly on the offset route. Here's a suggestion:

1. While on a normal leg, engage HDG SEL or HDG HOLD.
2. Enter and execute a RTE OFFSET of, say, 1 nm.
3. Check what x-track error is displayed on the PROGRESS page -- 0 nm or 1 nm?
4. Delete and execute the RTE OFFSET.
5. Re-engage LNAV.

This test may take just ten seconds ... :-)


|-|ardy

[cagarini]

Thanks! By the way, to check this out, you don't even need to fly on the offset route. Here's a suggestion:

1. While on a normal leg, engage HDG SEL or HDG HOLD.
2. Enter and execute a RTE OFFSET of, say, 1 nm.
3. Check what x-track error is displayed on the PROGRESS page -- 0 nm or 1 nm?
4. Delete and execute the RTE OFFSET.
5. Re-engage LNAV.

This test may take just ten seconds ... :-)


|-|ardy

Hey Jon, just make sure you don't end up testing the TCAS RA :-)

[emerydc8]

Here you go, Hardy. The test took a bit longer than ten seconds, but it is exactly what I ended up doing rather than getting a clearance to offset 15 right. Once executed, the x-track error is based on how far you are away from your offset route. No TCAS RAs on this one! https://youtu.be/W1qKwjSajsU

Cheers,
Jon

[Hardy Heinlin]

Fantastic. Many thanks! :-)


Cheers,

|-|ardy

[emerydc8]

Just an aside, LIFFT was the first waypoint on the SAMMR THREE ARRIVAL into El Paso and that's why we got the END OF OFFSET message in the scratchpad when I executed the offset -- The FMS will not let us offset on a STAR or SID.

[Hardy Heinlin]

I'm wondering what would happen if you were to enter an offset in 6R when you are already on a procedure (e.g. STAR etc.). Would the entry be (A) valid (and the ND would just hide the offset route, and LNAV will remain on the normal route), or (B) would the FMC deny the entry and say INVALID ENTRY? In PSX it's (A) ... and it will delete 6R after the next waypoint.

[Hardy Heinlin]

Profile points in general are now placed on offset routes when an offset is active, and the x-track error indication now refers to the offset -- in PSX update 10.36:

http://aerowinx.com/board/index.php?topic=4191.0


|-|ardy

[emerydc8]

I'm wondering what would happen if you were to enter an offset in 6R when you are already on a procedure (e.g. STAR etc.). Would the entry be (A) valid (and the ND would just hide the offset route, and LNAV will remain on the normal route), or (B) would the FMC deny the entry and say INVALID ENTRY? In PSX it's (A) ... and it will delete 6R after the next waypoint.

While on a SID or STAR, there is no offset feature displayed on the CDU, to wit, no place to insert an offset.

Jon

[Hardy Heinlin]

Aha!

Edit: Is 6R blank then? Or is another key displayed, e.g. "APPROACH>" or  "LEGS>" or something like that. I know on the ground it shows "TAKEOFF>".


|-|ardy

[emerydc8]

I think it's blank, but I'm off for a while, so I can't check it right away. I go to the United sim towards the end of the month. I'll try to check it there.

Jon

[emerydc8]

Hi Hardy,

Maybe you want to split this string off to a separate post on offsets, but I was talking to a friend over at a very large transportation company (whose name shall not be said), and he was telling me about departing out of CGO (Zhengzhou) and how it was SOP for ATC to tell them to offset to the right on a SID. He asked me if I knew how that was done and I could only guess it was done in HDG SEL.

Well, I learned something new here. Apparently, if you are on a SID or STAR where the OFFSET feature will not appear at 6R, the way you offset is to go direct to whatever your TO waypoint is, execute, and go back to the RTE 1 page. There you will see the offset. He said it works in both the sim (they actually teach this) and he did it a few days ago in the 744 with the legacy box. I would have never guessed. Here's a pic of his route briefing. Check the fifth box down on the right side under Remarks.

[Hardy Heinlin]

What if the direct-to fix still belongs to a procedure? I doubt that the RTE page will enable an offset then.

It's clear that the offset will be enabled if the direct-to fix lies beyond the procedure. I guess when ATC gives you a direct, that direct will usually skip the entire procedure. No wonder that this will enable the offset on the real aircraft and on the big sim -- and in PSX too.

The text says: "If given an offset on the SID". This can be interpreted in two ways:

1. ATC wants to see an offset "on the SID", and wants you to stay within the SID (with offset).

2. While the aircraft is "on the SID", ATC wants you to skip the SID by a direct-to out of it (with offset).


|-|ardy


It's a typical "double reference" that makes a language vague. Another example:

"I was told my hat is blue on the ground." -- That might mean:

1. My hat is blue and my hat lies on the ground.

2. While I was walking on the ground I was told my hat is blue.

[cavaricooper]

.. and a third-

My hat is Blue ON THE GROUND (and some other color when airborne)...



C

[emerydc8]

He said that if you are going to any waypoint on a SID or STAR and you bring that waypoint down to the s/p, up to 1L and execute, it will display the offset at 6R on the RTE page. Then you can offset -- even along your route to the original direct-to waypoint. The route briefing is a bit vague but he is 100% sure that it works in both the sim and the airplane. They do it on virtually every departure out of CGO and it is a stated offset (e.g., 2 miles right, 3 miles right). Of course, you can't offset before takeoff because the offset feature is never available on the ground, even using this technique above.

[Hardy Heinlin]

So we have three SID waypoints: AA, BB, CC.

I downselect AA and upselect it to 1L.

Offset is enabled, and I enter and execute an offset.

ND shows dashed offset line from aircraft to (abeam) AA.

Will the dashed line continue along BB, CC, and through the cruise segment till the first STAR?


|-|

[emerydc8]

Will the dashed line continue along BB, CC, and through the cruise segment till the first STAR?

It will continue to offset the entire SID for sure. Whether it continues to offset the route after the SID I'm not sure. I'll have to ask him.