# Elios 2 When to use the ATTI flight mode Elios 2 has several flight modes which can be selected by the pilot. Each have their own properties and uses. **ASSIST** is the default control mode, and must be engaged at the beginning of a flight. In this mode, several optical sensors around the drone will measure its distance and motion with respect to nearby objects. It uses this information to automatically remain perfectly stationary. However, optical sensors have limited range, and the quality of their measurements can be reduced by dust, direct sunlight, or featureless surfaces. In the **ATTI** flight mode, the pilot's inputs directly control the attitude of the drone and the optical sensors are not used. This control mode must be selected if the pilot notices erratic flight behavior due to the limitations of the optical sensors. {% embed url="" %} Some flight environments are more demanding on the stability system (and pilot) than others. You can use the [difficulty assessment sheet](https://drive.google.com/file/d/1__j-gm0QieSgylzL-eMcBuo21qZvw4nq/view?usp=drive_link) to estimate the difficulty level in function of several environmental factors. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://knowledge.flyability.com/aircraft/elios-2/elios-2-feature-details/elios-2-when-to-use-the-atti-flight-mode.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.