In the context of aviation and aerospace, an "Air Data Tester" (ADT) is a ground-based instrument used to test and calibrate the air data systems of aircraft, including pitot-static systems, air data computers (ADCs), and other related instruments.

An Air Data Tester is designed to simulate various flight conditions, such as altitude, airspeed, and temperature, to verify the accuracy and functionality of an aircraft's air data system. The tester generates precise and controlled air data signals, which are then fed into the aircraft's air data system to test its performance and calibration.

The primary functions of an Air Data Tester include:

1. Simulation of flight conditions: The ADT generates air data signals that simulate various flight conditions, such as takeoff, cruise, and landing.
2. Calibration of air data systems: The tester helps to calibrate the aircraft's air data system by generating known air data signals, which are then compared to the system's output.
3. Verification of system accuracy: The ADT verifies the accuracy of the air data system by comparing the system's output to the known air data signals generated by the tester.
4. Troubleshooting and fault detection: The tester helps to identify faults or errors in the air data system, which can be used to troubleshoot and repair issues.

Air Data Testers are typically used by aircraft manufacturers, maintenance, repair, and overhaul (MRO) organizations, and regulatory agencies to ensure the airworthiness and safety of aircraft. They are an essential tool in the aviation industry, as accurate air data is critical for safe and efficient flight operations.