Waypoints insertions

[bublegom]

Hi Hardy,

I found a little issue with waypoint insertion in the leg page of the fmc. If you delete a waypoint and try to suppress the route discontinuity created by entering the waypoint just before the route discontinuity it doesn't work. The waypoint is copied into the scratchpad but it is not inserted.
Workaround use the waypoint just after the route discontinuty.
PSX 10.43

Regards

François

[Hardy Heinlin]

Hi François,

this is a feature, not an issue. It has been tested on the real 744.

E.g. downselect waypoint #2 and upselect it into line #3. This will insert a disco in line #3. This is a real 744 feature and has been introduced in PSX 10.43. Doing the same step again will have no effect as the disco is already there. The real 744 FMC behaves the same.

Always close a disco by upselecting the next fix into the disco, not the previous fix.


Regards,

|-|ardy

[bublegom]

Hi Hardy,

Thank you for your answer. I don't really understand the logic of Boeing. The FMS doesn't allow you to insert the  waypoint just before the route discontinuity;  but it lets you use all the waypoints that precedes it (I know this action has no sense).

Regards

François

[Hardy Heinlin]

Look at it from the pilot's perspective: Your route is in front of you. You want to pass all the waypoints in front of you. You never want to make any leg longer by moving a certain waypoint further away from you. But -- vice versa -- you often want to make shortcuts by moving distant waypoints closer to you ("distant" in the sense of "listed legs"). So the more intuitive method is to bring distant waypoints to the disco, instead of bringing the aircraft and aircraft-side legs further away to the disco.

There are two pilot actions: Move a waypoint on the list further down, or further up.

There are two FMC features: When a waypoint is entered on the list, a disco appears, or disappears.

So there are 4 possible effects:

Waypoint up : Disco appears?
Waypoint down : Disco appears?
Waypoint up : Disco disappears?
Waypoint down : Disco disappears?

Now design a rule that turns these 4 possibilities in just 2 possibilities.
Not just Honeywell/Boeing, I think all FMC designers agreed to this 2-way rule:

Waypoint up : Disco appears
Waypoint down : Disco appears
Waypoint up : Disco disappears
Waypoint down : Disco disappears

This also has a logical reason: A disco is always attached behind a new entry, not before it. So when bringing up a new segment, it would be absurde to insert a disco somewhere inside that new segment.

Entering a new fix also inserts a disco. That trick is in the category "Waypoint down : Disco appears".

Of course, you can also create a disco by deleting a fix. But it's easier for the pilot if a modification inserts a disco automatically, especially when several legs are inserted. The disco helps to find the point where the new segment ends. It also requires a confirmation that the new segment has a reasonable connection; it will be confirmed by the crew by manually filling the disco.


Regards,

|-|ardy

[bublegom]

Thank you Hardy to have taken the time to answer me. I am going to read your explainations carefully and try to understand 

Regards

Francois

[Hardy Heinlin]

Here's a simpler picture:

When you enter route waypoints for your flight, the first waypoint you enter is typically waypoint 1, then 2, 3, 4 etc. You never enter waypoints in the reversed order 5, 4, 3, 2, 1.

As you want to enter route waypoints 1, 2, 3, etc., you need dashes or boxes always after the last entry. Not before the first entry. You add further waypoints at the end, where you enter 5, 6, 7, etc.

When you write a letter on a piece of paper, you start at the top. As long as the paper isn't full, there's always free space after your text, not before your text. You need the free space at the end because that's the place where you continue to write your text.

With this in mind, you can make an intuitiv rule: Always keep free space at the end of the entries, never before the entries.

So the keyword is: "After".

And so the sequence is: "1. Waypoint, 2. Disco". Not: "1. Disco, 2. Waypoint".

Because of this sequence, you can't fill a disco by adding a waypoint; the added waypoint will attach another disco after itself. You can only fill a disco by moving an existing waypoint (which lies beyond the disco) up the list into that disco (a reversed movement on the list).


|-|ardy

[bublegom]

In the creation of a route I easily understand, but what is not logic to me is when you suppress a waypoint in the middle of a existant route why are you allowed to insert one of the waypoints before the route discontinuity except the one just before the route discontinuity even it is a none sense but at least it can avoid the pilots to make errors.

François

[Hardy Heinlin]

... why are you allowed to insert one of the waypoints before the route discontinuity except the one just before the route discontinuity ...

Any waypoint before the disco won't close the disco. It's not only the one just before the disco.

It's a general, consistent rule.


|-|ardy

[bublegom]

You're perfectly right.

François