No place like home

Whether you are a new drone pilot or an experienced professional, you always need to review the basics and know exactly how the return-to-home (RTH) feature works with the drone you are operating. I have learned from experience, RTH can be your best friend in an emergency.

Before you just blindly trust the RTH function on your aircraft, take some time to become familiar with how to configure it and how it works; before every flight, ensure that it is properly programmed in case you need to use it. The default or typical settings may not be appropriate for your flight conditions.

As a public safety unmanned aircraft pilot, I am constantly flying under challenging situations. Sometimes flights do not go as planned, so RTH is my "break glass" emergency exit when things start to get out of tolerance. Sometimes, I engage RTH on the return leg from an extended mission when I am the most tired.

For the return trips, RTH is like autopilot in an airplane. I use it to reduce my workload when I can. However, as the FAA says, "While the autopilot relieves you from manually manipulating the flight controls, you must maintain vigilance over the system to ensure that it performs the intended functions and the aircraft remains within acceptable parameters of altitudes, airspeeds, and airspace limits."

RTH is your friend

Before you have to rely on the RTH function, you should understand what the settings are and how to configure RTH for safe use at the particular location where you are flying.

You want to make sure the automatic return altitude is set for a height above any obstacles in your operational area. I typically make sure the RTH altitude (to which the drone will climb or descend after the function is engaged) is 100 feet above the highest obstacle in my flight area. I do not account for towers because I never fly with a tower between myself and the aircraft. However, if I am flying in a hilly or mountainous area, I have to remember to adjust my RTH altitude based on the elevation of the highest hill, and account for the changes in terrain height across the entire flight operation area.

Remember that RTH altitude is always relative to the altitude of the home point (and that is not always where the flight begins). If the surrounding terrain rises 300 feet or more above the home point and your RTH altitude was set at 200 feet, the aircraft could fly directly into the ground.

To confirm terrain elevations around you, you can download a topographic map smartphone app—the one I use the most is Topo Maps US.

Also, know exactly where your home point is set, and that can vary. You do not want to make the same mistake I made in my early drone flying days. The actual location the drone might return to might not be the launch point. The home point may be set at the location where you powered on the aircraft, but if you move the aircraft between power-up and launch, bad things can happen. A tall tree taught me that lesson the hard way. The drone I fly now sets the home point at propeller start. This means if I am flying and land, turn off the propellers, and later launch while the aircraft remains powered up, as I sometimes do, the RTH function will send the aircraft back to where it last took off and not where it started the overall mission. Many systems also allow the pilot to adjust the home point during flight.

To determine how your particular aircraft establishes the home point, be sure to read your user manual.

Also remember that you have the option to take over. Engaging the RTH feature does not mean you become a spectator. During the return flight, you should be able to adjust altitude and airspeed while the RTH function is active. You can almost always stop the automated return function, usually by pressing the RTH button a second time.

Don’t be surprised

RTH can be engaged manually, but it can also be engaged by the software if your batteries are depleted, of if the aircraft loses contact with the controller. The threshold for triggering this automatic RTH event is typically configured through settings in your flight software. 

When your controller is unable to communicate with the aircraft in flight for more than a few seconds, the failsafe RTH function should engage and return the aircraft to the home point. I strongly recommend practice, so you become comfortable with how RTH works before you need to rely on it in an actual flight emergency. Again, the exact specifications of your failsafe RTH behavior should be reviewed in the user manual for your aircraft.

To get comfortable with failsafe RTH, I suggest you take your drone out into an open area, take off, fly to a point that is about 75 to 100 feet away and 10 feet above the ground, and hover. As you observe your aircraft, turn the controller off to simulate a lost signal event.

Watching your aircraft fly the automated RTH action a few times will help you to gain confidence and understand how the lost communications procedure works. You can always turn your controller back on after it begins the RTH operation, and you should regain control once the connection is reestablished. Having confidence in this feature is essential.

Recently I was flying a public safety demonstration flight with 125 law enforcement officers and firefighters watching. We had two aircraft in the air performing a search-and-rescue demonstration. For some reason, both aircraft lost radio communications and disconnected from the controllers in the same search area. Rather than panic, I had practical experience and confidence in the RTH process, and knew I had confirmed a safe RTH altitude for the operational area before flight. The aircraft returned as expected and made a pinpoint landing.

RTH is not perfect

There are some quirky elements of RTH. For example, if your GPS signal is weak and your system can only “see” a few satellites, the RTH function may not work at all.

If you trigger RTH when the aircraft is within about 65 feet from your home point, it may just land where it is. That could end badly.

Some aircraft have obstacle avoidance, which can adjust the RTH altitude based on things in the way. However, obstacle avoidance is not perfect, and the best way to avoid collision is to set the default RTH altitude to one that is safe for your operating area.