XM Satellite Weather, Interpretation

What factors do you consider when interpreting aviation weather?  If you’re using XM Satellite weather for enroute navigation then you should watch the Air Safety Institute Accident Case Study: Time Lapse click here.  This information alone is worth the price of an AOPA subscription.  It may extend your life and the lives of your family.

December 2011, a private pilot, in a Piper Cherokee Six (N3590T) was using NEXRAD weather to deviate enroute and avoid severe weather but the cross-country flight from Georgia ended in tragedy over Bryan, Texas when the wing-spar broke inflight and the left wing separated from the aircraft.  There were five souls onboard.  The pilot, his wife, his brother and two children died in the crash.

Aircraft destroying turbulence can and often does extend beyond heavy color coded areas of NEXRAD moisture reflectivity but it seems in this case “time lapse” might have allowed the weather to overtake the pilot’s navigational decisions.  You should pause and review the NEXRAD images and video commentary from about 8:58 minutes.  Notice the effects of XM Weather “time lapse” and the changes in NEXRAD moisture reflectivity.

Possible contributing factors

  • XM Weather Time Lapse
  • Not asking ATC for guidance and suggestions
  • Low visibility conditions (night IFR)
  • Stress and fatigue from a long flight
  • Hypoxia after 9 hours at high altitude (8,000 feet)

Interpretation considerations

  • Time Lapse
  • Storm cell bearing & speed greater than 15 knots
  • Tops over 30,000 feet
  • Destructive turbulence beyond NEXRAD reflectivity

Consider these other scenarios:

  1. Would you fly through an area of “yellow” NEXRAD reflectivity:
    1. With cell bearing and speed >15kts through your route of flight?
  2. Would you fly through an area of “yellow” NEXRAD reflectivity
    1. With cell bearing and speed >15kts through your route of flight;
    2. and echo tops >20K feet?
  3. Would you fly through an area of “yellow” NEXRAD reflectivity:
    1. With cell bearing and speed >15kts through your route of flight;
    2. With echo tops >20K feet;
    3. and a single XM lightning strike within 20nm of your route?

What additional “red flag” weather conditions would you look for in the above scenarios?  It’s helpful if you prepare in advance “red flag” criteria for XM Satellite Weather scenarios that you’ll not fly through.

The MFD time display of aging weather information does not indicate the lapse time from National Weather Service data.  It is a lapse time of an update from XM Satellite Radio.  And, published XM Satellite Radio refresh rates do not represent the rate at which actual weather is updated or new content is available.  Weather data is updated at intervals that are defined and controlled by XM Satellite Radio and its data vendors.

Although not thought to be typical, in extreme latency and mosaic creation scenarios, the actual age of the oldest mosaic in a NEXRAD image, can exceed the time indicated in the cockpit by 15-20 minutes (NTSB, Safety Alert, SA_017).  Even small time differences can have important safety of flight implications when considering fast moving weather, fast moving aircraft, changing intra-cloud intensity and extreme turbulence from strong storm cells that may extend out from the edges of NEXRAD images.

Recognize the common “5-minute latency” perception is not always correct.  Share with your fellow pilots the limitations of in-cockpit NEXRAD weather.

Warning: “XM Satellite Weather data provides information for avoiding hazardous weather.  Do not utilize XM Weather information to penetrate hazardous weather.”

The following poll is only for general aviation pilots flying piston-engine aircraft.



1) AOPA, Air Safety Institute, Accident Case Study: Time Lapse, Writer/Editor Brian Peterson, Project Manager Mike Pochettino

2) NTSB, Safety Alert, In-Cockpit NEXRAD Mosaic Imagery, SA_017

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