Knobs
 

Made you look....

The Embraer 195 MCDU has a rotary knob. No other CDU in my experience has had that, I've only ever seen a simple keyboard. What makes a knob a good idea?

Do the bawdy and then any opinion would be appreciated.

Is it for the brightness control?

Could you post a picture?

I once flew BAe 146s which had a sort of car radio sized navigation unit with just a knob on each end, a couple of push buttons and a one or two line green LED display. To enter a way-point, one knob selected the position of the letter you wanted to change, and the other knob turned to select a letter or a numeral. So to input 'NEDUL' for example, you would turn the first knob to move the cursor to the first letter position, then the second knob all the way through the alphabet until you got to 'N'. Then you rotated the first knob to select the second letter position, and rotated the second knob to select 'E' etc, etc. When you were done, you pressed one of the knobs to enter that way-point into your "flight plan". I say flight plan, but it could only store a few way-points, 12 maybe, and was very basic. No speeds or altitude restrictions. It just gave a steer command onto the HSI or the RMI, or something - can't remember now.

Anyway, the knobs saved on panel space - by not needing to have a dedicated key for each alphanumeric and all the functions. Is the Embraer 'knob' system similar perhaps?

B787 has a knob as an alternative cursor control...... strictly speaking not an MCDU maybe as keyboard is separate from the screen, but same function. Comes in handy as the touchpad is pretty poor.
Also a knob on older Airbus MCDU for screen brightness.

A350 & A380 have (track) balls...................

On the E Jets the radios are primarily tuned via the MCDU. Usually the numeric keys are used to input the frequency in a very convenient and direct manner, but it would also be possible to tune the radios in a more traditional way via the rotary knob.

Additionally the OAT and Assumed Temperature for the desired take off thrust setting must be entered/dialed in using the rotary knob. I always guessed this was a feature to avoid blunt mis-settings, as it would rule out finger troubles.