NEXRAD image on iPad
3 min read
NEXRAD image on iPad

Breaking news–this radar image could be 10 minutes old.

The NTSB recently made a startling (to it) discovery that there is latency involved with the Nexrad pictures that pilots are looking at as they try to avoid weather. To read the NTSB Safety Alert on the subject, you get the feeling that they just crawled out of a hole and discovered weather in the cockpit.

A quote from the NTSB Safety Alert in relation to the coverage of this: “…the NTSB has not found that such guidance contains details about the potential time difference between the age indicator and actual conditions.” They seem to think pilots have not been told that the age of the picture shown on the screen is just that and is not the age of the weather information used to generate the image. That is an insult to those of us who inform and educate pilots.

A quote from the April, 2003, issue of FLYING: I said when writing about the new Nexrad displays from Bendix/King and Garmin that, “Both systems have a way of identifying the age of the product that you see. The ages on metars and forecasts and pireps are an absolute. The Nexrad picture displayed by both systems does have an age in minutes shown on it but nobody has been able to come up with how the age relates to the time since the radar sweep actually examined a piece of weather. Maybe there is no specific answer to that question.  It could be something like from 10 to 20 minutes.”

Now, over nine years later, in discovering this, the NTSB, in the Safety Alert and in bright red bold type, says it could be from 15 to 20 minutes.

It was a while ago, but I remember that the people I talked to about this would not put a definite time on it because there are too many variables. It was the consensus that 10 to 20 minutes would be adequate to alert users to the fact that the information is far from brand new.

I have written many times since about Nexrad and I have always stressed that the age of the information is a factor in using Nexrad. I have explained that old-timers still prefer radar in the airplane for that very reason. Mac McClellan has written about this a lot, too.

I have also covered this in Air Facts videos for Sporty’s and have shown how the presentation of precipitation lags behind the development of a cumulus in real time.

But, alas, nobody has any sense but the NTSB. It took a lot of smarts for it to learn in only nine years what the rest of us learned at the beginning of the Nexrad program. In the Safety Alert, the NTSB cited two accidents where this was probably a factor. In truth there have been many such accidents and they will likely continue.

Sure, pilots will misuse Nexrad information. In truth, it is useful mainly in avoiding areas of weather. It does not work for the penetration of an area of weather and this has been repeatedly stressed.

For years I had Nexrad plus one of the latest airborne weather radar systems in my airplane. I had never enjoyed poking through a system, trying to avoid individual cells with radar. After I got Nexrad, I didn’t have to do that because I’d fly a lot of quality miles to stay the hell away from all the cells, as indicate d on Nexrad.

What has been your experience with this and do you think pilots look at Nexrad pictures through rose-colored glasses? Do you think he NTSB is out of touch?

Richard Collins
30 replies
  1. Linda berl
    Linda berl says:

    There is no place in this world I need to get to so badly that I would go anywhere near a cell!

  2. Aaron Daniels
    Aaron Daniels says:

    That seems to be the format of many messages that come our way. The numbers of acidents show we are not hearing/learning what you and the others are telling us.
    Since I’m a “light” IFR pilot my NEXRAD use is limited. It is an arrow in my quiver of flying those “quality miles” to have the smoothess ride and the most unplanned and most enjoyable stops that I can.

    • John Q Pilot
      John Q Pilot says:

      You make an excellent point, Aaron, one I think is at the root of the GA safety statistics. I work at a fair-sized FBO, besides being a pilot myself I also know and work with many pilots, ATP to Private, 1000’s of hours experience to less than 100, fly 500 hrs. year to 40 hrs. annually.

      While I strongly believe in continued learning/education and read Internet blogs such as this, articles, do AOPA & Wings courses, go to FAAST seminars when they’re local, read NTSB reports, watch training videos, etc. etc. all in the interest advancing my knowledge and safety as I realize none of us know it all.

      Few of the pilots I know do much of this, most do none. Doesn’t matter their experience level, same story… they “don’t have time for that stuff” or feel they know most everything, or some combination of the two.

      The we, as pilots, can further our knowledge in general the better and safer we are apt to be as a group in my opinion. It contributes to “more arrows in the quiver” as you said.

  3. Steve Phoenix
    Steve Phoenix says:

    My impression is that the NTSB is self-absorbed with their greatness and pushing various adgendas and not too interested in reality.

  4. Dave Wewers
    Dave Wewers says:

    It wasn’t news to me, but I think you’re over-estimating the exposure most pilots have had to this information in the past. Listening to the questions and comments at an IFR Refresher ground course some years back made me realize that many pilots do not spend the time to keep themselves educated and up-to-date on information that is extremely important to their continued survival!

    • Steve Severance
      Steve Severance says:

      You make a good point. Just because many of us are active in our continuing education doesn’t mean every pilot is. Last year at a seminar I watched a pilot argue with Tampa ATC when they explained why they wouldn’t clear him northbound through their central bravo airspace as it essentially made him a fish against the stream of incoming heavies. He wouldn’t listen to reason and eventually stormed out of the room. Kind of made me worry about how many there are up there just like him…

  5. James
    James says:

    I am a Weather Modification pilot in ND, although there is a delay in the information, proper realization of this makes NEXRAD a very powerful tool in what I do.

  6. Rich Gross
    Rich Gross says:

    I read into this a little differently. It seems to me that the NTSB knew all along about the delays. Like most government agencies, however, they are more reactive than proactive. I suggest that the timing of their bulletin is not caused by a lack of knowledge on their part, but an observation that there were enough pilots lacking that knowledge that action should be taken.

    • Scott Dennstaedt
      Scott Dennstaedt says:

      Here’s a statement in the alert…

      “The general issue of latency with in-cockpit NEXRAD is discussed in pilots’ guides, in industry literature, and on service providers’ websites. However, the NTSB has not found that such guidance contains details about the potential time difference between the age indicator and actual conditions.”

      Really? The NTSB isn’t close enough to general aviation to realize that this topic has been discussed ad nauseam and is as ubiquitous as the discussion of stabilized approaches vs dive and drive in the IFR world. I can recall how many articles are discussions I’ve read about satellite weather vs onboard radar. They are just out of touch with reality.

  7. Jeff Ingram
    Jeff Ingram says:

    Satellite weather in the cockpit is next to useless. Just another way for pilots to get ripped off. Big bucks, pilot mags promoting their sponsors, convincing the new pilots with $500,000 airplanes to get over confident and over their heads. If you do a proper weather brief before you start up, you will avoid the cells by doing an end run, arriving at your destination before they form, or staying on the ground if you can’t afford the time to go around them.

    • Dave Wewers
      Dave Wewers says:

      I couldn’t disagree with you more, Jeff. Sat weather in the cockpit ranks right up there with GPS as the best thing to enhance my flying in the 35 years I’ve been at it. I can’t tell you the number of times that in-cockpit NEXRAD allowed me to make a 5 or 10-degree course change hundreds of miles away from a line of storms to avoid them.

      • Scott Dennstaedt
        Scott Dennstaedt says:

        Agreed Dave. Having information is powerful. It can also be very dangerous if you don’t know how to use it properly. Satellite weather popped into existence and there was virtually nobody teaching pilots how to use it. The FAA is a decade or more behind the 8-ball and they have not even begun to incorporate this into their required curriculum. It’s a tool that has limitations. Understanding these limitations and integrating it into the plethora of other information available is the key.

  8. Larry Baum
    Larry Baum says:

    Like many government agencies, the NTSB seems to be wanting to justify their existence by making statements that is fairly obvious to anyone who has been paying attention. I suspect there is also certain amount CYA in them doing so. But it also appears that no one from the NTSB reads the aviation press. Like Dick mentioned, there were plenty of articles regarding NEXRAD latency when satellite weather was announced. So, in the end they are just restating “old” news!! Important – yes…new – no!

    We’ve had NEXRAD weather in our plane pretty much since it came out. For strategic purposes, it’s fantastic. We’ve been able to make and complete flights that would have been far more challenging without in-cockpit weather. And more than once, the NEXRAD display confirmed that our radar was wrong when it “claimed” that the precip would end in 20 miles. Having both works really well.

    And unlike the thoughts of some others, I think the overall cost is minuscule compared to the value. And today, the cost has gotten even smaller with the 1st generation ADS-B receivers coupling into iPads and other portable devices.

  9. Reid
    Reid says:

    I have used NEXRAD for five years and avoided many cells. I put the image in motion and fly at the trailing edge of the cell from 50 miles out or so making corrections. I have never had a cell be in my path using this method. The delay in the image insure the storm has moved more than indicated so the trailing edge is long- gone. Works for me.

  10. Andy
    Andy says:

    Dick I’ll bet it’s frustrating to see this urgent safety alert about something you’ve been preaching for ten years. I’ve been flying for four years, instrument rated for two, and flying in weather for one, so I’m probably the guy this is directed at.

    I’m not likely to get myself into trouble enroute. Using Nexrad at long range to divert around weather works great and is completely obvious. I’m making my decisions closer to the destination.

    I know about the latency of the radar data, but in hindsight I’ve been looking at the displayed age and not thinking enough about the additional time to collect, assemble, and distribute it. I should multiply by four or five!

    The NTSB is doing their job. So are you, because I would never have seen the bulletin had you not been willing to start this conversation one more time.


  11. Wayne
    Wayne says:

    I knew there was some delay, but never had to worry about it because we did not have the ability to get weather in the cockpit until now – iPad with the Stratus link. Maybe the NTSB was not that late in coming to the party, but alerting all of us that have recently started using the iPad that are not that familar with the issues.

  12. Charles Lloyd
    Charles Lloyd says:


    You hit the nail on the head about the NTSB. For them all I can say is DUH!

    I use NEXRAD and a Stormscope plus my eyeballs and briefings. NEXRAD lets you look so far ahead that you don’t need to get into a cell. I have made deviations of up to 200 miles laterally. When doing this type deviation early enough, you don’t add that many miles to a long trip.

    Radar would be nice but it doesn’t come on many GA singles. Besides NEXRAD is immune to masking that can be prevalent in a 10″ dish GA antenna. The 12″ dish in Citations does not do much good beyond 50 miles and it still had masking.

    NEXTRAD is just like any other aircraft system. You need to understand it before you can use it to your advantage. This is not the first time that the NTSB did the “Ready, Fire, Aim” trick.

  13. Doug Beck
    Doug Beck says:

    Knowledgeable, smart and careful pilots already know that NEXRAD weather data lags behind the real weather they are flying through. Unfortunately, there are a certain number of pilots that are none of those things. For a few of them, the NTSB alert might be a wake-up call.

    Regarding the idea that in-cockpit weather is a ripoff, I disagree. Weather is one of the key factors creating risk for airplanes, and any additional information pilots can get regarding weather is useful.

    I fly with ForeFlight on my iPad and the Stratus FIS-B receiver, which allowed me to safely and conveniently detour around a big area of thunderstorms recently on a flight between Chicago and Kansas City. My original clearance would have put me in the middle of the storms. While I was in flight and still more than an hour away from the leading edge of the weather, I was able to identify the problem, map out an alternate route, call ATC, obtain an amended clearance and get on my new course early enough that I avoided a hairpin turn right in front of the storm. How is that not a good thing?

  14. Michel Samson
    Michel Samson says:

    I agree with Dick- the NTSB report was somewhat confusing to me because I could not imagine that it was simply about the delay in the images, that we are told about repeatedly in every aviation publication, video and seminar on in cockpit weather . What’s next, NTSB learns that wings create lift making powered flight possible?! I think NEXRAD is superb and worth it for pilots, but like anything else you need to understand the equipment. Those pilots who don’t are not likely to be influenced by NTSB reports that are nine years out of sync with common pilot education. I enjoy reading everyone’s comments & the Airfacts Journal is fantastic.

  15. W S Webb
    W S Webb says:

    IFR is the way to fly. But it is not a license to fly “all weather.” I have been in hail in clear air.

  16. John Johnson
    John Johnson says:

    When I saw the NTSB report, I also thought to myself, “duh”, but Doug (above) is right:

    “Knowledgeable, smart and careful pilots already know that NEXRAD weather data lags behind the real weather they are flying through. Unfortunately, there are a certain number of pilots that are none of those things. For a few of them, the NTSB alert might be a wake-up call.”

    I can personally tell you that at our coffee drinking/lie swapping weekly meet at the airport, more than one pilot stated, “Did you hear that NEXRAD in the cockpit is actually delayed by up to 20 minutes?”

  17. David
    David says:

    I’m sure the NTSB is wondering “Are the pilots stupid or do they not just pay attention?”

    “Better put out a Safety Alert with Big Red Letters for those pilots seem unaware of the info in ‘pilots’ guides, in industry literature, and on service providers’ websites.'”

  18. Dan
    Dan says:

    The NEXRAD images are stale. Rather than warn pilots, why not decrease the latency? Processing the nationwide radar data to create a new image frame cannot take more than a fraction of a second with current computing technology. Just do it!

    For a couple years I used XM Weather with a Garmin 496 when commuting between Denver and Minneapolis. The main problem was the inability to receive an update from the satellite apparently due to heavy cloud cover or precipitation. It is annoying when a system works the worst when you need it the most.

  19. RG
    RG says:

    For years now we have been talking about the delays in radar information and still accepting 10 to 20 minute old pictures. Why?

    In this day and age of super fast computer processing and lightning fast data transmissions speeds (example of technological progress: this year I obtained fiber GB speed to my home), we should be focusing our attention on where the delays occur and how to speed the processing. There is no excuse that this data cannot be rendered and sent to our cockpits in a more timely manner.

    Let’s start putting pressure on the providers of this information chain to find the weak link(s) and improve an issue that we have “lived” with for far too long. Progress is overdue!

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