QUAD/RADIAL

[ASCTU744]

I wondered at which radial value the quadrants value changes. i.e. at 070 the quadrant is E and at 065 it's NE. And it seems that you can't enter radial only values (/XXX), is that right?

Thank you in advance!

-Nadir

[Dirk Schepmann]

On a typical compass, each of the 4 basic quadrants is divided at an angle of 45 degrees, which results in the definition of NE, SE, SW and NW. The 45 degrees angle is again split into two parts with an angle of 22.5 degrees (defining NNE, ENE, ESE, SSE and so on).

The FMC doesn't use this terminology, but I assume that 22.5 degrees to the left and right from N, S, E and W the FMC shifts to the next section (probably rounded up or down). So altogether you have 8 segments of 45 degrees. Technically, these are not quadrants anymore (because we have N, NE, E, SE, S, SW, W, and NW)  but that's nitpicking. :-)

And you can enter radial only values, just type in the number without slash (i.e. 210 instead of /210).

Cheers,
Dirk

[ASCTU744]

Thanks!
About the last part.... Boeing manuals say a slash is needed:

other Boeing and various airline FCOM's say the same.

[Hardy Heinlin]

Bulfer's 744 Guide (often refering to pilot reports), page 215, says: "It does not need a slash -- contrary to the slash rule."

[ASCTU744]

But with and without slash or without slash only?

[Hardy Heinlin]

I can't remember. I guess someone tested it on the real CDU and I programmed it according to that observation. The airlines that use PSX for FMC training have been happy with this behaviour.

[ASCTU744]

Oh, that's what counts👍

[Captain_al]

I can verify you do not need a slash when entering the radial. Nor do you need a slash if changing from right turns to left turns for the hold, just L works, or /L, but we always taught the least keystrokes method is better.

[Jeroen Hoppenbrouwers]

... uninformed guesswork below ...

Looking at it from a computer programmer perspective, you can take more syntax cues. Like, distance is always one or two numbers (0-99) and courses always three (000-359 or 000-360). "No slash required."

Safety wise though, you want to stay on the safe side and not assume that 20 is 20 and not 20x with a zero missing. So for numbers, the slash rule is required.

For turn direction though we are talking letters L, R which is much harder to accidentally enter instead of, say, course 3.

My guess is that the actual implementation of the slash rule was influenced by both the syntactical necessity from a programmer's perspective and safety considerations from an ops perspective. This may explain why in some cases the Slash Rule does not look consistent (consistency, of course, is by itself a good thing).


Hoppie