Air Data Test Sets: What Are They?

Flight instruments are crucial elements of aircraft, allowing pilots to maintain readings on various flight parameters such as altitude, attitude, airspeed, and more. Having measurements on such characteristics is paramount as it ensures that optimal flight paths are followed and hazards avoided. For this to be upheld, all instruments must function correctly and with ample accuracy. When one wishes to test their instruments for their performance, apparatuses known as air data test systems (ADTS) are used.

Also known as pitot-static test sets (PSTS), such apparatuses are pressure generators and measurement instruments capable of simulating the altitude and speed of onboard equipment for the means of determining airspeed, Mach, altitude, and altitude trend accuracy. As their alternate name suggests, air data test sets utilize the pitot-static system to conduct operations, the set connecting to the pitot tube and static port.

The pitot-static system is what allows many instruments to garner their readings, with pitot tubes and static ports collecting stagnation and static pressure respectively. These pressures are then used by various instruments to determine values like airspeed and altitude through the use of pressure sensitive instruments, gauges, and other such parts. With its role in flight safety, it is extremely important that pressure readings are accurate, lest one face the risk of various hazards. As such, one should use air data test systems when issues with accuracy are suspected, as it is always better to be safe prior to conducting a flight if anything is amiss.

In order to determine accuracy, air data test systems are able to simulate the pressure and vacuum conditions found in various settings so that measurements made by instruments can be verified or compared to expected results. This is very useful as it allows for testing to be conducted without having to remove any instruments or assemblies, reducing overall calibration times and maintenance costs. Air data test systems also make it very easy to calibrate a number of instruments such as the airspeed indicator, altimeter, vertical speed indicator, engine pressure ratio indicator, and manifold pressure indicator. Furthermore, they can also allow maintenance personnel to determine if there is a leak in the pitot system.

When using air data test systems, it is important that indicators are exercised and calibrated prior to use. With exercising, the indicators will be subjected to pressure levels that are close to the full-scale value of indicators before setting them back to zero-reference three times. After this, one can move onto calibration. For this step, each indicator will need to be calibrated within a range of ten equidistant points of the indicator, and any error in readings will need to be within manufacturer stated tolerances. Utilizing a correction chart, one can ensure that the indicators are performing properly before conducting tests.

While various conditions may affect readings during flight, we can utilize past data, mathematics, and other resources to have an idea of what instruments should read based on the simulated pressure and vacuum conditions created by air data test systems. As such, it is generally a matter of comparing expected results to what the instruments read during testing, and if there is deviation, further work can be done to ensure that everything is correctly calibrated and ready for flight.

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