# Identification Aircraft identification is a fundamental task in air traffic control, ensuring accurate tracking, communication, and coordination between controllers and pilots. Before issuing any ATC clearance in a **Surveillance Services** environment, an aircraft **must be positively identified**. ### Methods of Identification Aircraft can be identified using various methods: - **Unique Call Signs** – Each aircraft has a unique identifier associated with its flight plan. - **Transponder Codes (SSR)** – Squawk codes assigned by ATC for tracking and separation. - **Aircraft Type & Registration** – Helps verify aircraft identity, especially in mixed traffic environments. - **ADS-B Data** – Automatic Dependent Surveillance–Broadcast, providing real-time aircraft information. If a pilot selects an incorrect **SSR code or transponder mode**, ATC must instruct them to correct it. ### Radar Identification Surveillance radar systems provide **position, altitude, and speed data**, allowing controllers to track and correlate aircraft targets accurately. Radar identification is required **before providing ATC services**. When an aircraft leaves **radar coverage or enters uncontrolled airspace**, controllers must **terminate radar service** and inform the pilot accordingly. #### Level Verification - Controllers must **verify the displayed level information** at least once on initial contact. - The tolerance for verifying accuracy: - **±200 FT in RVSM airspace** - **±300 FT in non-RVSM airspace** If the displayed altitude **exceeds tolerance values**: ✔ **Ask the pilot to confirm the correct altimeter setting (QNH)** ✔ **If necessary, instruct the pilot to disable Mode C altitude reporting** Unlike **tower controllers**, who can visually observe aircraft, **radar controllers rely entirely on surveillance data** from various systems. ### Primary Surveillance Radar (PSR) #### How PSR Works - PSR transmits **electromagnetic waves** and displays reflections on the radar screen. - Each reflection represents an aircraft, but PSR does **not transmit aircraft identity information**. - Identification must be performed manually using **position correlation or maneuver-based methods**. #### Methods of Identifying Aircraft Using PSR 1. **Position Reports** – Correlating a radar target with a pilot's position report (distance & bearing from a known point). 2. **Departing Aircraft** – Assigning a radar target to an aircraft departing within **1 NM of the runway end**. 3. **Turn Method** – Instructing an aircraft to **turn by 30° or more** and observing the corresponding radar movement. 4. **Transfer of Identification** – Another controller transfers a positively identified aircraft to your control. ### Secondary Surveillance Radar (SSR) #### How SSR Works - Unlike PSR, **SSR actively interrogates aircraft transponders**, which reply with encoded data. - **Provides enhanced aircraft identification**, reducing workload and increasing accuracy. #### SSR Interrogation Modes
**Mode****Transmitted Data**
**A**4-digit squawk code
**C**Pressure altitude
**S**Callsign, 24-bit aircraft address, selected altitude, speed, etc.
Modes **A** and **C** are often combined as **Mode 3A/C**. #### Methods of Identifying Aircraft Using SSR ✔ **Recognition of aircraft callsign in an SSR label** ✔ **Recognition of an assigned discrete squawk code** ✔ **Observation of a pilot-acknowledged squawk IDENT activation** ✔ **Transfer of identification from another controller** The most **common method of identification on VATSIM** is **recognizing the aircraft ID (callsign) in an SSR label**. If a pilot is unable to activate their transponder, they can be identified using **PSR methods**. ### Reading and Deviations of Transponder Values While transponder deviations are **less relevant in a simulated environment** than in real life, controllers should still monitor transponder readouts for accuracy. - A flight level is considered **"reached," "maintained," or "left"** based on the transponder reading. - A **200-foot tolerance** is generally applied on VATSIM. - Any deviation beyond tolerance should be addressed with the pilot. Pilots should be reminded to **check their QNH settings** if an altitude discrepancy is detected. ### SSR & ADS-B in ATC Operations #### SSR (Secondary Surveillance Radar) vs. ADS-B SSR and **ADS-B (Automatic Dependent Surveillance–Broadcast)** are **complementary technologies** enhancing ATC surveillance:
**Technology****Function**
**SSR**Interrogates aircraft transponders to receive replies
**ADS-B**Aircraft broadcasts its own position and data automatically
#### Transponder Use in Ground Operations - **Before takeoff:** The transponder should be turned on before departure. - **At airports with ground movement radar (SMGCS):** The **correct squawk code** should be set before taxiing. For more details on **Surface Movement Guidance and Control Systems (SMGCS)**, refer to [Skybrary](https://skybrary.aero/articles/advanced-surface-movement-guidance-and-control-system-smgcs). ### Controller Responsibilities in Identification #### Before Providing ATC Services ✔ Aircraft **must be positively identified**. ✔ Identification must be confirmed **before issuing clearances**. ✔ Inform the pilot of radar identification **unless the previous sector already identified them**. #### If Transponder Issues Occur ✔ **Instruct the pilot to check transponder settings.** ✔ **If Mode C data is unreliable, request them to disable altitude reporting.** #### Loss of Radar Contact ✔ **If an aircraft leaves radar coverage**, radar service must be **terminated** and the pilot **must be informed**. ✔ **Procedural separation** may be required if radar service is lost.