diff --git a/gitbook/tools/flightaware/README.md b/gitbook/tools/flightaware/README.md
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@@ -156,6 +156,23 @@ The call sign is usually located primarily in two places. If looking at the flig
 
 <figure><img src=".gitbook/assets/Screenshot 2024-08-23 135843 - MARKEDmerge.png" alt=""><figcaption><p>Two places where users can find the call sign within the tool. One is through the live map on the landing page (left), and the other is through the specific flight page of the aircraft of interest (right).</p></figcaption></figure>
 
+
+
+<details>
+
+<summary>REGISTRATION NUMBER/ TAIL NUMBER/ / N-NUMBER </summary>
+
+**Definition:** This number appears near [the tail of every aircraft. ](https://elearning.aljazeera.net/en/journalism-magazine/osint-tracking-ships-planes-and-weapons)This is sometimes called a [“Tail Number” or, in the United States, an “N-Number”. ](https://www.bellingcat.com/resources/how-tos/2019/10/15/a-beginners-guide-to-flight-tracking/)[It is a unique number that tells you which country the aircraft was registered. ](https://www.occrp.org/en/project/russian-asset-tracker/faq-what-is-plane-tracking)This [guide specifies that an aircraft's registration is similar to a car's license plate, assigned when registered in a specific country.](https://www.bellingcat.com/resources/how-tos/2019/10/15/a-beginners-guide-to-flight-tracking/) This registration reflects the jurisdiction of the aircraft according to this [list](https://en.wikipedia.org/wiki/List\_of\_aircraft\_registration\_prefixes).&#x20;
+
+**When to use call signs for open-source investigations:** If available, registration information can be helpful in finding clues about ownership of the aircraft. However, there are a few caveats:&#x20;
+
+&#x20;_**1:**_  [_**The registered owner is rarely the actual UBO**_ ](https://www.occrp.org/en/project/russian-asset-tracker/faq-what-is-plane-tracking)_**(Ultimate Beneficial Owner - the person who profits or benefits from a corporate entity). It is rarely an individual but a company, trust, or charter/leasing company. In these cases, use additional sources to make the link.**_&#x20;
+
+&#x20;_**2: Aircraft registration can change,**_ [_**especially when sold to a new owner.**_](https://www.bellingcat.com/resources/how-tos/2019/10/15/a-beginners-guide-to-flight-tracking/)\
+
+
+</details>
+
 ## Cost
 
 * [ ] Free