KMD550 Video Performance

The KMD550 multifunction display (MFD) is normally used to display a moving map. Other display modes are for TCAS and GPWS data, and weather radar. The radar mode is implemented as a simple NTSC video input.

The purpose of this experiment was to see if the NTSC video performance is good enough for displaying text - specifically METAR/TAF data obtained via a satellite phone internet connection.

The simplest way to get the data is by using some kind of computer which interfaces to the satellite phone (details here) and which has a VGA output. This VGA output is then converted, using a low cost widely available converter e.g. this Startech one

to a video signal which connects directly to the KMD550's video input.

Unfortunately the MFD does not provide an interactive interface (there is no way to read the status of its buttons, for example) so the "computer" still needs to be pilot-accessible. At this point it was decided to keep things simple and support only textual METARs and TAFs. This also keeps the user interface simple; only the destination and alternate airports need to be pilot-configured and this can be done before departure.

Video Tests

The initial test was to see if the KMD550's video performance is any good at all. Since its official purpose is weather radar, it might well have been useless for text.

Using the LS800 tablet computer to drive the Startech video converter, the video worked straight away. Colours display quite well:

As expected, straight VGA performance was near-useless; one can just recognise the desktop of the 800x600 tablet computer

although frankly this is no worse than a normal television used in the same way. Only the very modern flat-screen HDTVs offer a monitor-like quality on this type of data.

Playing around with the font size and type, however, yields an entirely usable result with a 16pt bold font:

The above picture does not do it justice, due to poor contrast. The actual image is perfectly readable. I am not aware of any video quality adjustments on the KMD550. It is a straight tradeoff between font size, and how much data one wishes to display. One could fit the METARs for two airports on the screen.

A further quality improvement can be expected by running the computer at 640x480 or some other resolution which is close to NTSC's 525 lines.

Implementation

The set-up used for the above test is not viable for any airborne use - for example a mains power supply was required for the video converter, but it draws 9V and very little current.

One possibility might be the early-model PDAs which featured VGA output, for conference (overhead projector) presentations. Fitting this into a small case together with the video converter, and some software to interface to the satellite phone and grab the data say every 30 minutes, is completely feasible.

[to be continued]

Certification Issues

The KMD550 MFD tests described here were done on a bench. In reality, the only modification to the aircraft would be to bring out the KMD550's video input to a cockpit-accessible connector (50 ohm BNC, or perhaps SMA) and this would not present any approval problems. The rest of the equipment would be located within the cockpit in a "removable" manner. which sidesteps the need for an approval.

This page last edited 28th May 2009

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