Time was, all you had for in-flight weather updates was flight watch and a good look out the windshield. Over time, more fortunate pilots added lightning detection equipment to their weather-update capabilities. Those even more fortunate sought out airborne weather radar units. But in the past few years a whole new world of in-flight weather advisories has come into its own. Today, METARs, TAFs, airmets, sigmets, pireps, and other textual weather information — plus ground-based Nexrad weather radar imagery and other graphic products — can be beamed directly into the cockpit via digital datalink. All you need is a subscription to an information service, a compatible on-board transceiver and software for calling up the data, and a display screen and its associated hardware.
Datalink technology uses one of three}transmission methods: satellite; terrestrial stations broadcasting the FAA's Flight Information Services (FIS) data; and AirCell's ground-based cellular telephone network.
Echo Flight uses Orbcomm LLC's low-Earth-orbit data communications satellites. Weather information is privately supplied via Meteorlogix (formerly DTN). Echo Flight's is a two-way monitoring, tracking, and messaging service that lets pilots call up text and graphical weather information on a request-and-reply basis. In other words, you have to enter your information request on a cockpit-mounted keypad, send it in, then wait for the system to fill your order and broadcast it back to your airplane. Echo Flight's request-reply functionality also makes e-mail possible.
The big advantage of Orbcomm's satellite system is its coverage. Because satellite transmissions originate from space and can reach almost anywhere on Earth, airplanes can access information no matter where they are — at low altitude or high, and even when on the ground. The disadvantage: Request-reply access can be pricey.
Other satellite providers use broadcast-only technology. As the name implies, information is broadcast as a constant feed, and users simply tap into it. No request calls are involved. One such satellite provider in the works is Satellink Technologies' Merlin service, which uses the MSV (Mobile Satellite Ventures) satellite system. Satellink will offer Jeppesen DataPlan as its content provider. Subscribers to the Merlin service would get a receiver processor (target price "not much more than $1,500," Satellink says) that would be compatible with a range of multifunction displays, personal computers, and personal digital assistants (PDAs). Visit the Web site ( www.satellinktech.com) for details.
Another company that's pursuing the satellite-broadcast option is Vigyan Inc. Its PWA (Pilot Weather Advisor) service will also provide constant feeds of privately supplied text and radar data using the MSV network. Vigyan says the cost of its datalink receivers will be "between $4,000 and $5,000" and its monthly service plan will be less than $50 per month. This is a single-rate plan that provides unlimited access to all text and graphic products. For the latest developments on PWA, visit the Web site ( www.wxstream.com).
The FIS option uses two VHF frequencies that continually broadcast weather data and imagery. There's no request and reply here; instead the pilot just types his or her request (a METAR station identifier, for example, or the name of a Nexrad site) and the information pops up on the display. Because FIS uses ground broadcast stations, its signals have line-of-sight restrictions. This means that in many parts of the nation it's necessary to climb to 5,000 feet or more in order to receive signals. Near mountainous areas, where terrain can more easily block transmissions, even higher altitudes are needed. On the other hand, signal reception on the ground is possible where stations are located near airports in relatively flat terrain.
The FIS tower network is incomplete. As of this writing, some 30 towers are operational. Most of them are in the central United States. Full U.S. coverage won't be available until all 200 stations are up and running, which the FAA says will happen later this year.
Line-of-sight restrictions also affect AirCell's datalink capabilities. AirCell uses the same cellular telephone towers that serve conventional cell phones, but its signals are configured such that they don't interfere with them.
So far several avionics manufacturers have also announced their intentions to offer datalinked weather services, hardware, and software. More are in the developmental stage. Most make use of FIS to one extent or another, but some use private suppliers to customize their graphic datasets and provide more features. Here is a brief rundown of each manufacturer's capabilities, requirements, and costs.
AirCell
This Louisville, Colorado, company made its debut as a provider of in-flight telephones and telephone services, but has expanded its services way beyond voice-only. Its Guardian 1000 ("less than $4,000, uninstalled," the company says) lets you access FIS data, including Nexrad images, and display it on a panel-mounted multifunction display, a laptop PC, or a PDA. The Guardian 1000 doubles as a telephone, and in case of an emergency, dialing 911 on the panel-mounted keyboard connects you to the nearest air route traffic control center. Conversations are conducted via pilot headsets, using a dedicated channel on the airplane's audio control panel.
AirCell offers what it calls its Flight Guardian services for obtaining text weather and Nexrad imagery on a Compaq iPAQ PDA. The software for this service costs $99.95, and if you don't have an iPAQ, AirCell will sell you the software and the PDA for $649.95.
AirCell's DataComm 500 ("less than $2,000, uninstalled") can also provide weather information and lets you listen to ATIS and AWOS voice channels as well — but it's not a true airborne telephone. However, it can connect you to the Internet while in flight and gives you e-mail capability.
Monthly subscription costs range from $9.95 plus $1.99 per minute for data services only, to $29.95 plus $1.99 per minute for both voice and data services. For more information visit AirCell's Web site ( www.aircell.com).
Arnav
Like Honeywell Bendix/King, Arnav Systems Inc. plans to offer FIS products through its WxLink service. There have been ground station and other delays in Arnav's implementation schedule. Visit the Web site ( www.sagemavionics.com) for news updates.
Avidyne
This company sells the FlightMax DX50 datalink system, which goes for $2,950 ($2,450 for those who buy before the end of this month) and is designed to interface with the company's FlightMax flight situation displays. Avidyne will use the Orbcomm service and initially charge $29 per month for access. Service is set to begin in "mid-2002," says Avidyne. Visit the Web site ( www.avidyne.com) for information.
ControlVision's Anywhere Wx
Aircell doesn't have the corner on the weather-by-inflight-phone market. ControlVision's Anywhere Wx service uses a GlobalStar satellite telephone to route datalink weather to a Compaq iPAQ PDA. The equipment package includes the iPAQ, its plug-in 12-channel GPS receiver, the Anywhere Wx software, GlobalStar's GSP 1600 Tri-Mode satellite phone, and a universal yoke mount — all for an introductory price of $2,899. Options include a backup battery pack ($79) and a $69 carrying bag.
Anywhere Wx boasts a 15-second download time for national radar imagery, Nexrad radar, and text products such as decoded METARs and TAFs along your route of flight. Service plans run from $30 to $110 per month, plus per-minute charges from $1.49 to $1.29. The higher service tiers offer 5, 20, and 60 minutes per month of free calls. For a handheld moving-map display, weather information and the convenience of a tri-mode satphone that lets you place calls anywhere in the world, Anywhere Wx is a bargain.
Honeywell Bendix/King
Bendix-King has shipped about 50 of its KDR 510 datalink receivers at a price of $5,495 each. Its "Wingman" roster of datalinked weather services uses FIS (broadcast over Honeywell's proprietary ground stations, which format the data for Bendix/King receivers), and displays information on the company's KMD 550 or KMD 850 multifunction displays. A joystick can be used to maneuver a cursor so as to select text weather data from an airport, or select and~zoom in on Nexrad imagery. Graphic METARs that give color-coded depictions of ceiling and visibility are also available. The monthly service fee is set at one level — $49 — and includes Nexrad access. Full coverage east of the Rockies is expected by the end of this month, Bendix/King says. Visit the Web site ( www.bendixking.com) for information.
Garmin
Garmin opted to partner with Echo Flight for Orbcomm service. Its $3,495 GDL 49 datalink transceiver is designed to convey Echo Flight weather text and imagery to Garmin's 430 and 530 GPS nav/com display units. Text data will be free under Garmin's service plans, but Nexrad imagery will cost extra. For $9.95 per month, you get one free request per hour; any more and you pay $1.25 per request. Other service tiers range as high as $55 per month, which gives you 10 free requests per hour and unlimited access to textual weather. Visit the Web site ( www.garmin.com) for further information.
Echo Flight
This company has been selling its Flight Cheetah FL 270 flight computer/display units since 1998. The $5,295 portable unit isn't a required item. You can display the information on a laptop PC if you buy Echo Flight's EchoMap software and Orbcomm comRunicator. Service plans run from $9.95 ($1 for each access) to $55 per month (10 free requests per hour) and include 56-day navaid updates.
The graphic displays are worth a special mention. In addition to Nexrad imagery, color-coded displays of airport temperature-dew point spread, wind speed and direction, and ceilings and visibility can be called up, and so can Landsat terrain imagery. Approach chart overlays are available, and so are flight planning and e-mail services. Visit Echo Flight's Web site ( www.echoflight.com).
UPS Aviation Technologies
UPS is taking a comprehensive approach to datalink services. It plans to use AirCell technology as well as satellite access. The AirCell component would give customers telephone as well as datalink capability. UPS also leans heavily toward the Universal Access Transceiver (UAT) that it has been pioneering in its ADS-B (automatic dependent surveillance-broadcast) and FIS trials in Alaska. Having a UAT (UPS says its target price is $2,500) would give pilots both FIS and ADS-B (automatic dependent surveillance-broadcast) traffic information. The company is taking a hard look at the satellite broadcast services to be offered by Satellink Technologies and Vigyan Inc. No firm decisions or prices for equipment or services have been released, but UPS expects its services to be in place by early 2003. Look for updates on UPS's Web site ( www.upsat.com).
Datalink weather is the wave of the future. It can be costly, with the need for a dedicated receiver, monthly fees, and hardware and software requirements, but it also provides unparalleled weather awareness. Like other technological advances, however, any safety benefits depend solely on pilot judgment. You can have all the weather data in the world and still make a bone-headed decision. Expect to hear more about datalink weather services in the very near future.
E-mail the author at [email protected].
Nexrad vs. Airborne Weather
Because of datalink's digital transmission protocols, uplinked Nexrad weather radar imagery is depicted in pixels. Pixellated imagery can appear blocky and distorted on cockpit display screens, especially when zooming in on trouble spots at close range. This makes datalinked radar imagery useful for gross weather avoidance at distances greater than, say, 50 nm from contouring thunderstorm cells — which is where you want to stay anyway!
The big advantage of uplinked radar imagery is the absence of precipitation attenuation. Ground-based Doppler Nexrad weather radars are so powerful that they can "see" right through heavy precipitation, and produce distortion-free representations of storm cell structure and extent — both vertically and horizontally. That's because these radars operate at such high power ratings and use such huge antennas.
General aviation airborne weather radars, on the other hand, are saddled with low-power, small-antenna problems. All but the most powerful weather radars — ones with 30-plus-inch-diameter antennas — can't detect distant storms. By the time radar signals make the trip from your antenna, bounce off a storm cell, and return to your antenna a lot of signal energy has been lost — enough to make a big storm cell look small, or not appear at all. Airborne weather radar also has big limitations when flying in or near areas of moderate to heavy precipitation. That's when radar returns reflecting off heavy rain can prevent you from seeing past immediate areas of precipitation and blind you to the most violent cells lurking just a few thousand feet ahead. Known collectively as attenuation, these shortcomings can kill. So airborne weather radar often is not the ultimate storm avoidance tool — even though there are many who swear by it.
Uplinked radar imagery is free of attenuation and therefore gives accurate depictions of precipitation. This is the datalink advantage. The down sides are the blocky pixellation and 5-minute update schedule (that's the national network's update rate; onboard datalink updates can be further apart.) If you're trying to pick your way through a line of thunderstorms — not a good idea in piston-powered airplanes flying at low altitude — those clunky-looking boxes of red, yellow, and green and that slow update cycle can give you dangerously misleading information. "Five minutes? Slow?" you might wonder. Oh, yes. A whole lot can happen in a big hurry in thunderstorm environments. Just ask anyone who's been there. Two minutes can be an eternity.
For in-close avoidance, airborne weather radar is preferable, but only if it comes with an antenna larger than can be accommodated in most airplanes with maximum gross weights less than 12,500 pounds. The ideal setup? Datalink plus airborne weather radar. The datalinked Nexrad can give you plenty of warning should storm cells form in the distance and let you steer well clear of the worst buildups. The airborne unit is useful for skirting air mass thunderstorms and storm clusters, when you need rapid updates and better image resolution of fast-changing storm contours.
The best advice of all: Maintain visual separation from all building cumulus clouds by at least 20 nm — more if you're flying above the freezing level. That's where most lightning strikes occur and where cloud movement can be the fastest. — TAH
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