Avionics News April 2012 - 21

One device’s picture indicated “clear flying here,” but the other two virtually screamed “run for cover.” Across the grounds, Mother Nature’s fury trashed a small number of planes and sent uprooted tents sailing downwind in the maelstrom, as we pondered the dramatic difference in the tablet’s computer-generated view and that of the other computer. “What gives?” was the question reflected on the faces of a dozen pilots – half of them active users of portable tablets and EFBs. Their expressions prefaced remarkably similar responses: “Really glad I’m not depending on that for my flying.” Three used similar combinations of datalink service, receiver and tablet. We saw slightly different images from two others packages with a different hardware device, a different brand-name EFB with datalink capabilities using a different datalink receiver than the tablet’s, but the same subscription service. Anyone flying toward Oshkosh using the EFBs or panel-mounted datalink images probably landed short at Fond du Lac about 20 miles south. Anyone using the tablet – well, they should have been able to see the maelstrom early enough to avoid it – wondered aloud why it was so far off. The original image displacement put the storm cell’s closest edge about 40 miles from its actual location, a massive error for even the strategic planning that datalink weather is best used. Let alone any tactical maneuvering inspired by the images. Latency is certainly a known issue for datalink. It varies with the systems, but generally, latency impacts the recency of an image with any location errors due solely to the time lag in image delivery. It is important to fathom. It’s also important as an avionics shop to understand when

recommending datalink weather systems to customers. Absent the knowledge of how and why these disparities occur and how to gauge the differences could spell disaster for your customers. There are reasons for the issue, ways to gauge whether a unit suffers from such issues and ways to augment datalink with the intent of gaining a more accurate, close-tocurrent image. First and Foremost, It’s a Processing Thing A survey of avionics makers, software engineers and computer-hardware folks produced an image of graphics reproduction in aviation devices limited by the same constraints we find occasionally slowing our progress with other computers: system memory, processing speed and the capabilities of the graphics-processing common to computers and avionics alike. Users value tablets, by and large, for their extensive flexibility and broad capabilities, such as the ability to run a writing or browsing program while maintaining and processing information via a wireless Internet connection and one or more pages online – and showing it all through the graphics processor as controlled by the programming for the touchscreen interface. It’s a lot of “ones” and “zeros” rushing about the computer. A tablet with eight gigabytes of memory has its hands full; ditto for one with 16 gigabytes, though it will be noticeably smoother and quicker. Load up a tablet and 32 or even 64 gigabytes may be needed to allow all the software to work without the machine swapping information back and forth – possibly even prioritizing some demands to run later or in background.

Shutting down everything but the weather is one solution. But, if you’re trying to use a tablet fed by a GPS module with the charts and plates georeferenced to your position, you are putting a lot of demands on the processor and its memory. Add on the weather data and its demands on the main and graphics processors, and things may slow down – par-

ticularly machines with limited memory. Trade the tablet for an EFB specifically designed for the job of serving up charts, plates and procedures with the GPS integral to the system – in reality a baseline function – and the system’s demands are more easily handled with memory and processing tailored to the role. Even EFBs that lack an integral datalink weather receiver tend to perform as quickly and as timely as EFBs with a built-in datalink receiver. But, the EFB won’t be connected, or trying to connect, to outside devices or services. The narrow focus of the EFB serves the user of the EFB’s functions well.
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Avionics News April 2012

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