Morning,

 

I was just browsing around on Youtube and I came across this video taken from the flight deck of a Dash 8-Q400.

 

 

Its a brilliant video showing a first person view of a CATIIIa approach through the HUGS. As you can see the information regularly appears and then vanishes. Could anyone tell me anything about this as i cannot think of any situation when it would be useful to have this especially in a hand flown approach.

 

I was also wondering since the layout looks similar to that on the NG if this was something that is on the real NG but not in PMDG's FSX rendition.

 

Thanks

This isn't a feature. This occurs when you use a camera to film a projected picture, because the cameras recording frequency (pictures taken per second) and the displaying frequency of the projecting device (pictures projected per second) aren't synchronized.

I thought of that, however I don't think that is what this is. If you watch the video information selectively dissapears and reappears, even in the middle.

think it only cycling between different functions of the hud to show the different aspects of the hud is

I thought of that, however I don't think that is what this is. If you watch the video information selectively dissapears and reappears, even in the middle.

 

It is indeed caused by the camera shutter speed being faster (and out of sync) with the refresh rate of the display.

 

There are two ways to draw images on CRT-type of electronic display - raster graphics and vector graphics.

 

Old fashioned CRT computer monitors, (such as we all used before the advent of inexpensive flat screens), as well as old fashioned (pre HD) televisions use raster graphics. In a raster display, the image is drawn in a series of very narrow horizontal "strips", by a tightly focused beam of electrons. The beam starts at the upper left corner of the display, and scans across to the right side, drawing one "line" - then it snaps back to the left side, and drops down a small amount, and draws the next line. This process repeats until the entire screen has been scanned - producing one "frame". Then the beam moves back to the upper left, and starts drawing the next frame, line by line.

 

If you photograph a raster-scanned display using a camera with a fast shutter speed, you will see an effect where part of the screen is fully filled in, and the rest of the screen is blank. You can even see this effect if you look at a CRT display through the moving blades of a variable-speed fan.

 

Aircraft displays use "vector" graphics. In a vector system, the individual graphics elements are individualy "drawn" by the electron beam, exactly the way a person would draw an image on a piece of paper using a pen or pencil. If the display was set to display something simple - say an "x" in the center of a circle, the beam would first be moved in a circle in the center of the the screen. Then the beam would shut off for a moment, reposition, turn back on and draw one line of the "x", then shut off, reposition and draw the second line - then repeat by refreshing the circle etc...

 

That is why you see the effect in the video you posted - each individual component of the PFD image in the HUD is individually drawn - e.g. first the speed tape, then the altitude tape, then the command bars etc. This all happens much faster than human vision can detect, so when viewing a vector display with your eyes, you see all elements of the image as always being present - but a high shutter-speed camera can reveal what is really going on.

 

There is a third way of displaying images electronically - which is the way that flat screen LCD computer and HD TV set use - in which each individual pixel that makes up the complete image is mapped to an array of memory locations, and all pixels are turned off or on simultaneously.