Flight Planning: Aviation Weather

By Brandon Guillot, RPC, MAS

Weather is one of the most significant elements that can affect the safety, reliability, and even effectiveness of small UAS flight—but it may also be one of the most ignored topics when it comes to preflight planning. As such, the cautious small UAS pilot will ensure that proper attention is given to considering weather, and its effects on the mission, prior to beginning any flight operations.

First, one must consider the potential effects of weather from both a safety and mission effectiveness standpoint. Wind, visibility, separation from clouds, and density altitude all play a significant role in how a small UAS will perform. Of these, wind is probably easiest to detect, and also has the most immediate effect on your aircraft.

Effect of Wind on Drone Flights

For illustration purposes, a Cessna 172 has a maximum takeoff weight of around 2,300 lbs. compared to your sUAS that weighs less than 55 lbs. Yet that Cessna 172 (which weighs nearly 42 times your drone) is limited to a 17 knot crosswind for takeoff and landing, or else its directional stability is going to be severely compromised.

As a Flight Instructor in my youth put it: “Anything above 17 knots of crosswind, and you’re a Test Pilot.” Wind can produce severe turbulence for your sUAS, particularly on the leeward side of obstacles, as well as consuming precious battery time while trying to reach your objective or even return to your launch point. Visibility and separation from clouds play crucial roles by allowing your flight crew to observe manned aircraft and take evasive action as soon as possible to prevent a midair collision.

Density Altitude

Lastly, a change in Density Altitude such as an increase in temperature, humidity, or launch altitude, or a decrease in atmospheric pressure is going to make your aircraft work harder to reach its assigned altitude or destination. This means using elevated levels of caution during hot, humid days, particularly for those who are flying in areas of the country that are significantly higher than sea level. Remember the old rule of thumb on Density Altitude: “If you are sweating, the aircraft is sweating!”

Under Part 107, the FAA has listed weather minimums that certificated airmen operating sUAS must follow. You must have at least 3 miles visibility at the control station, as well as remain 500 feet below the cloud deck, and 2000 feet away from the clouds horizontally.

The intent of these minimums is to ensure that sUAS operations are taking place in clear airspace that would allow numerous opportunities for the flight crew to see and avoid any manned aircraft that enter the flying area. As a result, it is vital to ensure that your flying area meets the proper minimums for both safety and regulatory reasons.

Follow Drone Manufacturer’s Recommendations

At the same time, it should be noted that the FAA does not provide any minimums for wind conditions and density altitude. Instead, sUAS pilots are encouraged to read the documentation particular to their aircraft regarding these two items. The UAS Flight Manual or Pilots Operating Handbook produced by the drone manufacturer will list the specific limits that are recommended by the designer in order to prevent any dangerous conditions.

For that reason, it is also crucial for all sUAS pilots to thoroughly study the manuals provided for their aircraft in order to know the capabilities, and limits, provided by the companies that have conducted the Research and Development necessary to draw those conclusions. Anyone ignoring those limitations does so at their own risk, and opens themselves up to a host of potential problems.

Best Aviation Weather Apps & Websites

Since weather is an essential element for safe sUAS flight planning, it begs an important question. How do you determine the weather conditions, such as wind speed, visibility, and cloud height? Fortunately, technology has provided a number of potential options that pilots can use for their planning and Aeronautical Decision Making (ADM) purposes:

•  Websites such as www.1800wxbrief.com or www.aviationweather.gov use airport-based weather observation systems to create the METARs and TAFs we all had to decipher as part of our Part 107 test. Both are free to use, and even provide the service of decoding METARs and TAFs so you do not have to!
•  If you are in the field, there are mobile apps that can provide similar information derived from the same airport-based detection systems. AeroWeather Lite is a free app that provides METARs and TAFs in real time, but be warned—you will have to decode them yourself, unless you want to register for the paid version. At the same time, apps such as NOAA Aviation Live will provide decoded airport information for free. There are also some excellent drone-specific weather apps, such as Aura, that will provide weather, airspace, satellite, and No Fly Zone information in a single location. However, be prepared to pay for a subscription service to fully use their functionality.
•  Lastly, there is one app that I get a lot of questions on, and I both recommend it and discourage it. The Weather Channel app does not provide a lot of the information we need in the field to maintain safety and separation, namely visibility and cloud height, so I tend to encourage other sources for those critical elements. However, the Weather Channel app does provide a very important service by using the GPS in your smartphone to warn you when lightning strikes within a certain distance of your location. As such, the app may not be the most useful for flight planning—but it could save the lives of your crew or yourself if a sudden thunderstorm develops.

Above all, remember the potential effects that weather can have on your flight, your crew, and those around you. Weather deserves to be considered as a part of your flight planning, and should be high on the list of items you examine when deciding if you will fly or not. Technology can do a lot to help us make those decisions, and ensure that our flights are conducted in a way that benefits our crews, our customers, and the public in general. But it is always up to safe and responsible sUAS pilots to gather the information and make their decisions from there.