Avionics News October 2012 - 24

LIGHTNING DETECTION & DATALINK
Continued from page 22

source and receiver are designed to work together – and require paying a subscription fee set by the datalink provider. Some aligned with a portable device’s electronic flight bag or flight-planning program may use the network of a mobile-phone service. One service is, however, free to those who buy a compatible receiver. Regardless, these systems generally update the data about 10 times an hour – reflective of the six one-minute sweeps of a Doppler weather radar antenna that produces the composite image we’re used to seeing. After completion of the six sweeps, the system needs a bit more time to compile the image, update other information and uplink or transfer the package to the broadcast system before broadcasting the package. So, while updates occur generally at six-minute intervals – slightly faster in some cases – images and data generally will be a few to several minutes older. An indicator on the display screen usually gives an age for the data. Some text data, METARs and TAFs only update when new ones are issued – generally, just before the top of the hour, unless a special update occurs – so those pages don’t change as often as the graphics. Most weather datalink systems include a page showing lightning strikes compiled from a ground-based lightning-detection network and included on the same basis as the Doppler weather radar – a compilation from the prior cycle. It’s these latency issues that prompt service providers and hardware makers alike to universally advise against using the Doppler radar or lightning-strike images tactically, or for real-time course changes and decision making as one might with onboard weather radar or spherics. Even the newest image is simply too old to be useful for real-time navigating. Conversely, watching a multifunction display run the animated replay of one, two or three hours of updates can help pilot decision-making based on a storm’s trends and track. Three hours would be 30 snapshots long and play like an animated film, one frame after another, during the span of about three to five seconds. While onboard radar may stay the real-time champ in storm avoidance, even this technology, spruced up with 21st century digital and color technologies, cannot deliver what datalink delivers: the ability to examine the entire country, see whether more storms lurk behind the one in front or deliver text weather, pilot reports and graphics depicting lightning, IMC conditions and more.
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avionics news

Weather-Avoidance: Electrical Avoidance Tools Spherics devices have come a long way since the introduction of Paul Ryan’s original Ryan Stormscope WX-7 at the 1976 Reading Air Show. The basics remain the same: an AM radio receiver – the detector part – listens for static characteristics of a lightning strike, calculates a bearing angle and distance, and puts a representative mark on a display screen showing relative bearing and estimated distance from the airplane. The originals used rudimentary, low-resolution, three-color liquid-crystal displays; later models used CRT displays or other technologies. Today’s systems employ several display types, as well as the ability to display the data on a multifunction display, primary flight display or dedicated hazard-display system screen. But, the basic science remains the same, while the sophistication of the processing and distance gauging has greatly improved. Today, three companies provide the bulk of lightning detection systems: Avidyne, which several years ago merged with Ryan and now produces an advanced version of the original Stormscope; L-3 Avionics, which produces the progeny of Ryan’s original; and Insight Avionics, which produces its own self-contained Strikefinder. Avidyne The company’s TWX670 Tactical Weather Detection System was the first tangible result of Avidyne’s absorption of Ryan, and the package advanced the state of the art considerably over what was already a well-developed technology. Working in the TWX670’s color-contoured TWxCell Mode, each cell grid is displayed as a hexagonal array of cell weights (colors). Color-filled hexagons highlight the most intense regions of thunderstorm activity, presenting a visually contoured color display with dynamic sectors. Operating in Cell Mode permits the pilot to quickly identify the most intense regions of thunderstorm activity. According to Avidyne, the TWX670 combines the data of all lightning activity occurring during a running threeminute period, regardless of the number of strikes. This provides a meaningful dynamic map of the lightning discharge rate and density for immediate TWX670’s TWxCell Mode visual acquisi-

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october

2012

Avionics News October 2012

Table of Contents for the Digital Edition of Avionics News October 2012