Weather On the Go

Information available to pilots after takeoff keeps getting better.

Datalink Weather

Datalink Weather

** Datalink weather has been available for years, but
it's never been better thanks to improvements
(shown here on an Avidyne MFD).**

It's hard to overstate the benefits of having access to a wealth of weather-related information in flight. Armed with a full arsenal of datalink weather capability, onboard weather radar and lightning strike detection gear (not to mention what we can often see in front of us with our own eyes), pilots today are able to fly more trips with greater confidence than ever before.

For strategic decision-making, the datalink weather information that we can call up in flight is a true boon to safety. When conditions turn out to be worse than forecast, we can see the location of fronts and storm systems hundreds of miles away and plan accordingly. There’s no telling how many lives have been saved or bad situations avoided because of datalink weather gear. Without question, the technology has changed the way we fly for the better.

Still, as is the case with any advanced cockpit capability, there are caveats to consider. For example, studies have found that pilots who regularly fly with in-cockpit weather technology are more likely to take risks and fly closer to storms than those without access to such information. A 2003 study showed that the better the resolution of the Nexrad radar data, the more time pilots spent looking at their weather displays and the longer they waited until diverting around dangerous thunderstorms.

When it comes to tangling with storms, we pilots know the magic “safe” number by heart: 20 miles. That’s the minimum distance we’re told we should maintain when flying in the vicinity of convective weather. The figure was chosen because this is how far from a storm cell we can expect to encounter severe turbulence, strong outflowing updrafts and downdrafts and microbursts. And as we all know, in too many cases our airplanes might be unable to outclimb these strong localized air currents or, if we’re really unlucky, important pieces like a wing or the tail could be torn off.

Do pilots always maintain the 20-mile minimum safe distance from storms? Perhaps a better question is, which pilot is more likely to give storms a wide berth, the one whose cockpit is equipped with the latest and greatest Nexrad weather equipment or the guy who is flitting along with no weather-detection gear at all? Smart pilots know that Nexrad images downlinked from a satellite or ground station might not tell the whole story. What’s important to understand is that if you fly without onboard weather radar or a lightning strike finder, the information you see on your multifunction display might be incomplete or too old to be reliable.

Nexrad Considerations

The National Transportation Safety Board has become so concerned about the phenomenon that it recently issued a safety alert warning pilots about the inherent latency of in-cockpit Nexrad weather displays. The alert came just weeks after the crash of a Pilatus PC-12 over Central Florida after the turboprop single broke up in flight while maneuvering around powerful thunderstorms. The NTSB has yet to release its final accident report, but here's what we know so far:

At about noon on a hot day last June, the pilot of the PC-12 departed St. Lucie County International Airport (FPR) in Fort Pierce, Florida, bound for Freeman Field Airport (3JC) in Junction City, Kansas. Also on board were his wife and four children, all headed home after a vacation in the Bahamas. Fueled up and ready to go, the pilot departed on an IFR flight plan and was cleared to climb to FL 260. As the PC-12 headed northwest in the vicinity of Lakeland, Florida, the controller advised the pilot that his radar was painting a large area of precipitation with “extreme” echoes. The controller recommended a deviation to the right. The pilot agreed, asking for and receiving a heading of 320 degrees. This was the PC-12’s last communication with Miami Center.

According to preliminary radar data, the airplane turned to the northwest and climbed to 25,100 feet before entering a rapid descent. The pilot of a nearby airplane reported hearing a Mayday call about one minute before picking up the sound of an emergency locator transmitter signal. Eyewitnesses reported seeing the airplane emerge from the clouds in a spin and shedding pieces before descending into a field, killing all aboard.

Although the NTSB has yet to rule on a cause, less than two weeks after the crash the Board issued its safety alert warning pilots who use in--cockpit Nexrad weather display equipment that the “age indicator” denoting when the data was transmitted can be misleading. In fact, the actual Nexrad data you see on the screen can be as much as 20 minutes older than what is stamped on the cockpit display. The NTSB noted that this difference can present “potentially serious safety hazards to aircraft operating in the vicinity of fast-moving and quickly developing storm systems.”

Obviously we won’t know what role weather may have played in the Florida PC-12 crash until the NTSB releases its final report, but it’s clear investigators are becoming increasingly concerned about the role cockpit technology can play in weather-related accidents.

The details of two other recent crashes highlight the causes for concern, says the NTSB. In one such case last year, the pilot of a Piper Cherokee Six experienced an in-flight breakup and was killed near Bryan, Texas, after flying into severe storms. The NTSB determined the pilot’s Nexrad cockpit weather display would have shown he was clear of severe echoes when in reality his track put him directly into the teeth of a storm due to the data-transmittal latency issue.

In another fatal accident, this one in March 2010, the pilot of a Eurocopter AS350 was using his onboard satellite weather receiver to divert around a powerful storm cell near Brownsville, Tennessee. As he attempted to land, the Nexrad display would have indicated he was clear of precipitation based on a one-minute-old radar image. In fact, the image was at least five minutes older than that, and, unluckily, a severe storm was just passing over his home base as he arrived.

In these accidents, the pilots apparently failed to adhere to the 20-mile rule for operating near thunderstorms. Even if they had accurate data in the cockpit, they were still too close for comfort — and appeared to be using their datalink weather information for close-in tactical maneuvering. With the wrong information, they unwittingly set themselves up for disaster.

The fact is, the downlinked Nexrad weather data you see on the display in your cockpit is always older than what the time stamp indicates. The reasons make perfect sense: First, the radar station has to sweep past the storm that will eventually show up on your cockpit display. Then that data is transmitted to National Weather Service computers, which prepare the data for dissemination. Next, the data is transmitted to your service provider, such as the FAA in the case of FIS-B transmissions or to XM Satellite Weather or WSI InFlight in the cases of paid satellite services. Finally, the data is coded, rebroadcast and received in your airplane. All of this takes time — and maybe a lot more time than you would have guessed.

Makers of in-cockpit weather-data receivers have been warning about this phenomenon for years. Most pilots probably already understand the data they see on their display has some inherent latency, even if they don’t realize just how old those blobs of green, yellow and red can actually be. The bottom line is, pilots need to understand that weather avoidance is still their responsibility. Controllers can do only so much to help out since their primary responsibility is to ensure safe separation of IFR traffic. Just because you have that XM Nexrad display or the latest digital weather radar doesn’t mean you should take risks you wouldn’t in absence of such technology.

It’s important to understand that our weather equipment should be used for strategic planning and not tactical maneuvering. Once we accept this limitation of in-cockpit weather data, we can focus on the benefits — and there are a great many, obviously.

XM on Your iPad

By far the most popular choice for pilots is the XM Satellite Weather service, an extremely useful and popular tool for strategic weather decision-making that includes not just Nexrad imagery but also winds aloft, icing levels, turbulence reports, areas of IMC and VMC conditions and more. There’s really no need to dive too deeply into the XM WX service since it has been around for years, but what you might not know is you can now buy a portable data transmitter for $199 and display all of that great XM information on your iPad, Android or other mobile device.

WxWorx, the provider behind the XM service, last summer launched Mobile Link, essentially a Wi-Fi transmitter that takes the data from your already-installed XM weather receiver and broadcasts it to your handheld tablet. This fall, WxWorx improved the product by adding support for up to four devices simultaneously. The only downside is that you must already have an XM weather receiver in your airplane for the Mobile Link unit to function.

Another choice for in-cockpit weather is the WSI InFlight service transmitted over the Sirius satellite network. This is the choice of Avidyne for its MLB700 weather receiver, which also doubles as a Sirius audio programming receiver. Avidyne also offers the MLX770 weather data receiver, which is capable of transmitting data over the Iridium satellite network for coverage anywhere in the world where weather data is disseminated. The XM and Sirius products, as you probably know already, are limited to the United States.

Free ADS-B Weather

A prediction we’re hearing more and more is that the availability of free ADS-B weather data is going to put the XM and Sirius services out of business. So why aren’t pay services quaking in their shoes? The ADS-B mandate begins in 2020, and it’s a safe bet that a great many buyers will choose to add weather capability when it comes time to upgrade. Still, many pilots who often fly in marginal or worse weather say they’ll never give up their XM service because the data they receive is so much better.

Given the choice between XM or ADS-B weather, I'd pick XM every time since ADS-B coverage can be spotty and it has limitations in what you can do with it. But as the FAA builds out the ADS-B coverage network and improves the data it transmits, there's no question the free weather service will grow in popularity. It's happening already with the sudden interest in portable ADS-B weather receivers, including the Stratus unit from Sporty's and Appareo systems, which seamlessly links with an iPad running ForeFlight Mobile. Garmin has followed suit by introducing the GDL 39, a portable ADS-B weather receiver that can also receive limited ADS-B traffic data. And new to the market is the XGPS 170 portable ADS-B weather and traffic receiver from Dual that works with popular apps such as WingX Pro7 running on iPads or Android devices.

Still, these ADS-B-based weather choices are also hamstrung by the image-latency issues the NTSB is so concerned about. Bottom line, if weather information is being delivered to you via a datalink, it’s not real-time. For a more accurate picture of the weather ahead, pros say nothing beats onboard weather radar or, if you’re on a budget, a lightning strike detector.

If you're thinking "cha-ching!" when you read the words "onboard radar," you aren't alone. Weather radar is big bucks. But the good news is prices are coming down. Garmin, for example, which entered the radar business a few years back by buying an older Narco design and making it better, is now offering quite a lot of capability at an attractive price point.

By all accounts, Garmin’s first radar, the GWX 68, was a good one at a good price — about $18,000 uninstalled. But it was also merely a taste of what was to come. This summer Garmin took the wraps off the GWX 70, a brand-new solid-state weather radar completely of Garmin’s own design that catapults the Olathe, Kansas, maker into a league alongside the big boys at Honeywell and Rockwell Collins. Compared to earlier-generation magnetron-based weather radar systems, Garmin’s digital radar offers significant improvements in capability, reliability and cost of ownership — the GWX 70 hits the mark in all three of these areas by bringing advanced capabilities that were formerly available only on high-end business jets using radars that cost upward of $100,000.

What’s different about Garmin’s newest radar? Available in antenna sizes of 10, 12 and 18 inches, the GWX 70 includes a feature called Altitude Compensated Tilt that makes the pilot’s job much easier by eliminating the need to reset the antenna tilt after changing altitude. To use the feature, simply adjust the GWX 70 once to the desired tilt angle and the radar automatically maintains that level during any changes in altitude. Another cool feature is called WATCH (weather attenuated color highlight), which helps identify the shadowing effects of storm cell activity, highlighting areas where radar signals are weakened and may not fully reflect the “storm behind the storm.”

The GWX 70 also offers horizontal scan angles of up to 120 degrees, or pilots can focus radar scanning on a specific area of interest, from a small slice of the sky of 20 degrees all the way out to its maximum. Finally, a ground-mapping mode lets the pilot use the GWX 70 to scan terrain features for visual navigation, and the system also includes a vertical scanning function to help analyze storm tops, gradients and cell buildup activity at various altitudes.

Garmin also offers a couple of options for the GWX 70, the first being turbulence detection out to 40 nautical miles. Ground clutter suppression is also available as an option, which allows the GWX 70 to automatically separate radar ground returns and remove them from the display. The GWX 70 is compatible with the full line of Garmin multifunction displays, including the GTN series touchscreen avionics, the G1000, G2000, G3000 and G5000 integrated flight decks, the G500/G600, the MX 20 and the GMX 200. Uninstalled price for the GWX 70 starts at $20,995.

Not to be outdone, Honeywell and Rockwell Collins have introduced some amazing radars of their own, which are capable of scanning radar images into their memory and processing the data to create 3-D models of storms and dissect the weather hundreds of miles ahead.

Other Weather Options

If you aren’t quite ready to spring for onboard radar, another good option for real-time weather detection, as we’ve noted, is a lighting strike finder. L-3 Avionics Systems’ Stormscope line of lightning mapping systems has been one of the most popular for many years. This is the same basic technology that has been around for a long time, under the ownership of a number of companies, including Ryan, 3M and Goodrich Aerospace.

Another choice is Avidyne’s TWX670 lightning strike finder, which wins out over the Stormscope in one regard: It can detect strikes from 0 to 25 nm while the L-3 unit does not. Personally, I’d like to know about close-in strikes even though I realize I’m not supposed to be flying this near to storms. Neither the Stormscope nor the TWX670 can see precipitation, but by detecting the electrical activity present as storms build, this technology can provide an accurate and early view of areas to avoid. Having both Nexrad and real-time lightning detection offers an undeniable edge.

The latest Stormscope products can interface with a variety of cockpit displays and are capable of showing lightning strikes at ranges of 25, 50, 100 and 200 nm, 360 degrees around your current position. The units update lightning information every second and include a “strike rate indicator” that tells you whether a storm appears to be building or dissipating. Most popular among the GA crowd is the WX-500 model, which can integrate with just about any MFD sold as well as panel-mount avionics such as Garmin’s G1000, Avidyne’s Entegra and Rockwell Collins’ Pro Line 21 systems. L-3 also offers the WX-950 Stormscope, which uses a high-resolution, 3-inch display/processor, and at the top of the model range, the WX-1000, which is capable of supporting Arinc 429 EFIS inputs for higher-end installations in business aircraft.

Whatever technology you decide to include in your cockpit, understanding the benefits and limitations of your equipment can help you avoid making the kind of serious mistakes that can lead to problems in flight. And remember, no amount of in-flight weather technology can guarantee that you won’t inadvertently end up someplace you’ll wish you weren’t. Avoiding those kinds of situations goes back to proper preflight planning, a solid understanding of meteorology basics, knowing your airplane’s performance and always having a Plan B for when forecast conditions turn out worse than expected.