Air Data Test Sets, also known as Pitot-Static Testers, simulate aircraft pressure and vacuum conditions to perform a number of measurement functions to test and verify an aircraft’s pitot-static system instruments without the need to remove them from the aircraft. This can reduce the calibration time and overall maintenance costs.
They can perform a leak test an aircraft’s Pitot-Static system and are capable of calibrating the airspeed indicator, altimeter, vertical speed indicator, manifold pressure, and engine pressure ratio (EPR) indicator.
Newer Air Data Test Sets have software-controlled user interfaces that provide protection to both the test set and the aircraft instruments and make it easy to operate for all experience levels of personnel. Most also have RVSM approval that indicates they meet the required accuracy standards to ensure compliance with those specific regulations.
Air Data Test Sets are useful tools and provide critical support to aircraft operators and maintenance personnel.
The Pitot-Static system is a collection of instruments used on the aircraft to measure the static pressure (Ps) and total pressure (Pt). The altitude and airspeed of the aircraft are calculated from the various relationships between those pressures and the temperature at the flight altitude.
The major components of the traditional Pitot-Static systems with mechanical instruments, are the Altimeter which determines the aircraft’s altitude due to changes in air pressure, the Airspeed Indicator that shows the aircraft’s speed relative to the surrounding air and the Vertical Speed Indicator (VSI) which shows the rate of climb or the rate of descent. Most modern aircraft make use of an Air Data Computer (ADC) that calculates the airspeed, rate of climb and altitude from the total and static pressures obtained from the pitot tubes and static ports on the aircraft.
It is critical that the Pitot-Static system meets the reliability and accuracy standards to ensure the safety of the aircraft. Failures or inaccuracies in those systems can develop into life-threatening situations. The use of the Air Data Test Sets in the calibration of those systems can verify that those systems are functioning correctly.
Air Data Test Set Calibration Process
The calibration of Air Data Test Sets requires a stable pressure and vacuum source and a highly accurate pressure Dead Weight Tester to simulate the required pressures needed for the instrumentation.
A visual inspection is first performed on the Air Data Test Set to look for obvious signs of damage to the pressure ports, hoses, power cables display and other components of the test set.
A Leak test is performed on both the Static and Pitot sections of the test set. Readings are typically taken one minute apart at pressures between 75% and 90% of the full-scale value of the system instruments to determine the leak rate.
Exercising of Indicators
Each of the indicators will need to be exercised before the calibration of the specific indicator can begin. This is accomplished by subjecting the indicators to a pressure near the full-scale value of the indicators and then back to its zero-reference three times. Once this is accomplished then the calibration of the indicators can occur.
Calibration of Indicators
The indicators should be calibrated at approximately ten equidistant points within the range of the indicator. The error in the readings must be within the manufacturer’s stated tolerances for the unit being tested. The mechanical indicators typically have a correction chart made of the test points and associated errors to assist the aircraft technician when using the test set in the field.