Drone Safety & Risk · Lv1 Beginner · about 20 min
Pre-flight checks and emergency response
Work through the pre-flight check in the order "visual check before power-on → checks after power-on → final check before takeoff → low hover". You may touch moving parts only before power-on, and if anything is wrong you choose to fix it, replace it or not fly.
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What you will learn
- Work through the pre-flight check in the order "visual check before power-on → checks after power-on → final check before takeoff → low hover", and explain why it goes in that order
- Look at a fault found during the check or a calibration warning and make the "don't fly" call yourself
- Explain the types of failsafe (auto return, auto land, hover) and how to think about return altitude and the battery turnaround point
- When the link is lost, the battery runs low or GNSS is lost, choose your first action by following the priorities (drone → where to go → communicate)
Checks and the go/no-go call
Stop it before you fly
The pre-flight check is your last chance to keep "not flying" on the table. Any hazard (a source of danger) you find can be removed safely while you are still on the ground.
The order has a reason. You may touch propellers and other moving parts only before you power on. Once the power is on, keep your hands off and check using the screen and your surroundings.
On many drones you power on the transmitter first and the drone second, and power off in the reverse order. This varies by model, though, so the drone's manual always comes first.
If you find a problem, put safety first, even if it keeps the client waiting. You can only choose to "fix it, replace it or not fly today" while you are on the ground. Each stage catches different problems: a loose part shows up in the visual check before power-on, a wobble shows up in the low hover. You cannot skip any stage.
What the check covers, and the no-go call
What you are looking for in the check is anything that could make the drone lose thrust or position in flight. When you find something, you have three options: fix it, replace it, or don't fly today. If you put your reason into words, you can explain it to the client too.
- Before power-on: look at the propellers, motors, screws and battery for chips, looseness, swelling and damage
- After power-on: look at the warnings, satellites, charge, settings and home point on the screen for warnings, shortfalls and wrong settings
- Before takeoff: look at the people, obstacles and wind around you for approaching people, unexpected obstacles and strong wind
- Low hover: watch the response, sound and stability for lag in control response, unusual noises and tilt
You don't do a sensor calibration every time. Do it when the drone asks for one, when you fly far from where you last flew, and after transport or a hard knock. Follow your model's manual for the procedure and how often to do it.
- Compass calibration: in an open outdoor spot, away from steel frames, rebar, cars, magnets and smartphones, rotate the drone as the screen instructs
- IMU (inertial measurement unit) calibration: place the drone on a level, stable surface and wait while it stays completely still
- If the calibration fails or the warning won't clear, move somewhere else and try again; if it still won't clear, don't fly
A swollen battery, a chipped or cracked propeller, a calibration warning that won't clear: none of these is a reason to "fly and see how it goes". A calibration warning that won't clear is telling you the sensor readings can't be trusted. Don't use a swollen battery; set it aside, away from other things, and handle it as described in "Getting to know drone parts" and the manufacturer's instructions.
Failsafes and GNSS loss
A failsafe lets you decide in advance what the drone does when something goes wrong. The typical options are auto return, auto land and hovering in place. The names and the behaviors you can choose differ from drone to drone.
GNSS loss means the satellite position information is no longer available. With nothing left to hold position by, a drone that relies on GNSS alone to hold position doesn't stop when you let go of the sticks; it drifts in the same direction as the wind. Because it no longer knows where it is, some drones can't use auto return or hold position at all, and the behavior depends on the model and its settings. Check your model's manual beforehand.
In a 2 m/s wind, wind speed × time (20 m in 10 seconds) is a rough guide to how far a drone that was standing still will drift. It may drift less, but if you lose GNSS while moving, the drone carries on further with its momentum, and gusts or the stronger wind higher up push it further still. A separate position sensor, if the drone has one, can sometimes help.
Auto return assumes the drone knows its own position and the home point. If there is a tower about 35 m tall but the return altitude is 30 m, for example, the return path runs straight into the tower. But higher is not always better either. Set it too high and the climb and descent eat battery, and the drone spends longer in the air. Too low means obstacles, too high means battery, so decide the return altitude and how the return ends (return or land) on site, looking at obstacle heights, people under the route, whether you are over water, and your battery margin.
Exercises in this part (solved inside the lesson)
- Put the check in order
- A small chip in a propeller
When something goes wrong
Priorities when something goes wrong
When something goes wrong, act by the emergency priorities: (1) keep the drone safe, (2) decide where to go, (3) communicate, in that order. In aviation this is known as Aviate-Navigate-Communicate. If you settle the order in advance, you won't hesitate even when you are rattled.
- link loss (loss of signal): first watch what the drone does (the behavior you set, e.g. auto return), then move people away from the area
- Low battery: first bring the drone down without starting anything new, then decide where to land
- GNSS loss: first hold the drone so it doesn't drift, then land it somewhere safe
Decision flow on link loss
- Keep your eyes on the drone and confirm that the behavior you set has started (here we use an auto return setting as the example; with an auto land or hover setting, watch for that behavior instead. Controls vary by model)
- Tell the observer, and move people away from the return point and from under the route
- Move to a spot with a clear line of sight, adjust the antenna orientation, and try to reconnect
- Even if you reconnect, don't make big stick movements right away. The drone may still be in the middle of its auto return, so check the flight mode on the screen before deciding whether to take over
- After landing, recover the drone, record what happened, and contact the people involved. The record feeds into your next flight
Exercises in this part (solved inside the lesson)
- Lose GNSS, hold it and bring it down
- Check items and what they prevent
- Set the return altitude and behavior
- What to do on link loss
Turning back and wrapping up
The battery turnaround point
Coming back takes as much battery as going out. To get home with your reserve intact, set a turnaround point before you fly. If you only think about it once you are out there, there may not be enough left to come back.
Example: take off at 100% and keep a 20% reserve: (100 − 20) ÷ 2 = 40%The simplest estimate, assuming the outbound and return legs use the same amount.
The 20% reserve is a guideline often used in training, not a legal requirement. It is set by the operator's or the drone's policy. On a day with a tailwind on the way out, you will have a headwind on the way back, and cold days or flights with a lot of climbing also use more, so keep a bigger reserve. The battery indicator is only an estimate too, so don't rely on it down to the last percent.
Setting up battery warning levels helps you make the call to come back. As the charge drops, the warning escalates from "low" to "critical" to "emergency", and the drone shifts step by step toward returning or landing. The levels and behaviors vary by drone.
Three checks before you fly
- Check: Go through the four stages in order. If something is wrong, choose to fix it, replace it or not fly; never "wait and see".
- Settings: Check the return altitude and the behavior on link loss and low voltage against the obstacles, people and water at the site. What the drone does on GNSS loss varies by model, so check the manual.
- Turnaround point: Keep a reserve, and fix the battery you may use outbound as a number before you fly. On a headwind day, keep a bigger reserve.
Checks done as a team, such as read-backs, challenge and response, and the authority to stop work, are covered in "The basics of an operations team". Here we stop at the patterns you can apply on your own.
Next comes the final exercise. You will make a series of decisions across one day, from the check to the landing. Remember: the drone before communication, "fix it or don't use it" rather than "wait and see", and no new maneuvers after a warning.
Checks, settings and turnaround points all exist to reduce risk. Close calls, when reported and shared, become material for future safety. Reporting is not about blaming anyone; it is about not repeating the same thing. Reporting systems are covered in "The basics of an operations team".
Exercises in this part (solved inside the lesson)
- Battery you may use outbound
- From the check to the landing
Summary
- Work through the pre-flight check in the order "visual check before power-on → checks after power-on → final check before takeoff → low hover". You may touch moving parts only before power-on, and if anything is wrong you choose to fix it, replace it or not fly.
- A failsafe switches the drone to a safe behavior set in advance (auto return, auto land, hover) when something goes wrong. Decide the return altitude for each site, looking at obstacles, people, water and battery.
- When something goes wrong, act in the order "drone → where to go → communicate". A drone that holds position by GNSS alone won't stop when you let go of the sticks after GNSS is lost; it drifts with the wind, so hold it and bring it down.
- The battery you may use outbound, starting fully charged, is (100 − reserve) ÷ 2. The reserve percentage is set by the operator's policy; on days when wind or cold will make the return leg cost more, keep more in reserve.
In Lv2 you identify the causes of danger, assess risk by likelihood and severity, and prioritize countermeasures.
Terms in this lesson
- pre-flight check
- The procedure of checking the drone, battery, transmitter and surroundings in a fixed order before flying, and deciding not to fly if anything is wrong.
- failsafe
- A mechanism that switches the drone to a safe behavior set in advance (return, land or hover) when something goes wrong, such as link loss or a low battery.
- auto return
- A maneuver in which the drone, typically after a fault, climbs to a preset altitude, flies back over the home point (usually the takeoff spot) and lands. Commonly called RTL (Return to Launch), or RTH (Return to Home).
- link loss
- The state in which the radio connection between the transmitter and the drone is lost. Also called loss of signal; the drone then acts according to its failsafe setting.
- sensor calibration
- Measuring and correcting the offsets in the outputs of the compass, accelerometer and other sensors using a set procedure. Follow your model's manual for the procedure and how often to do it.
- emergency priorities
- The principle that when something goes wrong, you think in this order: (1) keep the drone safe, (2) decide where to go, (3) communicate.
- battery warning levels
- A setting that escalates the warning from "low" to "critical" to "emergency" as the charge drops, changing the drone's behavior step by step toward returning or landing.
- GNSS loss
- Losing the position information from the satellites. The drone can no longer hold its position and may be carried away by the wind.
- turnaround point
- The point, set as a battery level, beyond which you must not go if you want to return with your reserve intact. You set it by estimating consumption on the way out and on the way back.
Try it yourself
This page is the text of the lesson. The exercises and simulators run inside the lesson.
Go to the exercises of “Pre-flight checks and emergency response”
Read this lesson in another language: 日本語 · Español · Français
Updated · The simulators are simplified models for education