Making Safer Decisions with Onboard Weather
By Jason Blair, FAA Designated Pilot Examiner, ATP, CFII, MEII, AGI | April 2014
Not long ago, GA pilots had limited access to weather information in the cockpit
during flight. The last decade has seen a significant increase in the availability
of onboard weather information as portable devices have advanced to provide near
constant connectivity in the cockpit. Devices such as the new ADS-B receivers that
connect to electronic tablets or availability of XM weather on portable GPS devices
provide continuous access to radar, TAF, and METAR allowing pilots to make better
and earlier en route decisions.
Making Earlier Weather Related Decisions
Historically, when flying across country we got our weather information from a ground-based
radio station report such as ATIS, AWOS, ASOS or sometimes broader information from
HIWAS stations. Many times the range over which we could hear these reports was
limited, especially when flying at lower altitudes. Decisions related to the winds,
ceilings and visibilities at our destinations were left to the last few miles of
our flight, shortly before setting up for an approach. That late in a flight, it
is less likely pilots will break off an approach in marginal weather.
Imagine a flight during which we receive a METAR for our destination. The winds
are 15 gusting 25 from 300 degrees with a 400 foot overcast ceiling. The airport
has an ILS for runway 16 and a VOR approach for runway 30. The VOR approach brings
us down to 700 AGL and the ILS brings us down to the standard 200 AGL. What should
we do? The VOR approach is unlikely to break us out of the clouds and the ILS is
going to give us both significant tailwind and crosswind components. Neither of
these seems ideal.
Would your decision be different if you had already descended from your cruising
altitude 20 miles out than if you were 100 miles away at altitude? Perhaps finding
a nearby airport might be a better choice. I think we are more likely to make better
diversion decisions if we have the time to really think about the consequences of
the weather and can consider better options. Onboard weather gives us access to
this information earlier helping us make more informed decisions.
Avoiding Weather En Route
The same holds true when considering en route weather diversions. Most light GA
aircraft historically have not had onboard radar information. In a few cases, lightning
strike finders or, in rarer instances, onboard weather radar systems were available.
Now, Nexrad is available to virtually all pilots in any aircraft. The ability to
reference storm cells, lightning data or even just broad areas of rain allows you
to consider re-routing the flight path. Doing this farther out, you can create greater
distances between your aircraft and the weather you want to avoid. Over longer legs,
the ability to adjust course earlier requires a smaller percentage of total distance-change
on the overall flight than if we alter our route when close to weather.
Another benefit of an onboard Nexrad weather feed is that it lets you “see behind”
the weather. In some cases, traditional onboard weather radar displays didn’t always
let the pilot see beyond the front edges of weather, especially when it was heavy.
This didn’t allow him or her to strategically plan for what would come next. Instead,
it limited the pilot only to plan tactically for what was immediately in front of
Of course, combining traditional radar or lightning detection displays with Nexrad,
along with good ATC coordination, can result in an optimum weather-picture to make
decisions. Remember, you can always ask for help interpreting weather based on what
ATC sees on their displays. There is no excuse for being surprised by weather when
equipped with these tools.
When using radar feeds, be sure to know the limitations of the systems. There is
an inherent latency in the information that is presented due to upload and data
transmission times. This doesn’t mean the data isn’t valid, just that you have to
know how “old” it is. This type of in flight-weather avoidance should be used for
larger scale planning to help you avoid larger areas of weather, not to skirt specific
cells of storms at close proximity.
Having this information is not an excuse to skip getting a weather briefing. It
isn’t a way to “get closer to weather” to shorten your route. There are limitations
to the systems. It is important to know them and understand them, and to know how
to properly use the systems. If you have questions about systems in the aircraft
you fly, find a good instructor or fellow pilot who is familiar with the systems
and learn about them. This is best done on the ground, not in the air when you are
trying to penetrate a scattered line of thunderstorms on your first long cross-country
flight for a family vacation.
The upgrade to modern weather information in the cockpit offers a savvy pilot a
way to make weather-based decisions in their flights earlier than ever before. These
advances in instrumentation have the potential to impact the safety of their flight,
helping to ensure that pilot and passengers may enjoy many more years of GA travel.
Jason Blair is an active single and multi-engine instructor and FAA Designated Pilot
Examiner with 4,600 hours total time and 2,600 hours instruction given. He serves
on several FAA/Industry aviation committees and is the past Executive Director of
the National Association of Flight Instructors. He also consults on aviation training
and regulatory efforts for the general aviation industry.
does not provide technical or legal advice, and is not affiliated with companies
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contained herein. Content is for general information and discussion only, and is
not a full analysis of the matters presented. The information provided may not be
applicable in all situations, and readers should always seek specific advice from
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authors, and should also not be regarded as technical or legal advice.