Air Data Test Sets / Pitot Static Test Sets

Air data test sets (ADTS) or Pitot-Static test sets (PSTS) are pressure generators and measurement instruments that simulate the altitude and speed of onboard aircraft equipment. They are commonly used in aviation to monitor the accuracy of an aircraft’s airspeed, Mach number, altitude, and altitude trend readings. The name ‘Pitot-Static’ is derived from ‘Pitot & Static’ tubes on the aircraft which are connected to the testing instrument.

 

A pitot-static system typically consists of a pitot tube, a static port, and pitot-static instruments. Other components include air data computers, flight data recorders, altitude encoders, cabin pressurization controllers, and various airspeed switches. Errors in pitot-static system readings can be extremely dangerous as the information obtained from the pitot-static system, such as altitude, is potentially safety-critical. Several commercial airline disasters have been traced to a failure of the pitot-static system. Pitot Static Test sets are therefore used to ensure the accuracy of aircraft instruments.

 

Pitot-Static System – Operation Principle:

As mentioned above, a pitot-static system comprises two critical components: the impact pressure chamber and lines and the static pressure chamber and lines. These systems act as the source of ambient air pressure to operate the altimeter, vertical speed indicator, and airspeed indicator.

 

Impact Pressure Chamber and Lines: In this system, the impact air pressure (air striking the airplane due to its forward motion) is derived from pitot tubes mounted in locations with the slightest disturbance caused due to the airplane’s motion through the air.

 

Static Pressure Chamber and Lines: The static pressure (still/ambient air pressure) is derived from the static line attached to a vent mounted flush with the fuselage side to compensate for variations in static pressure due to the airplane’s attitude. The static chamber is vented through tiny holes to the free, undisturbed air, and as the atmospheric pressure increases or decreases, the pressure in the static chamber changes accordingly. This pressure change is again transmitted through lines to the aircraft instruments (altimeter, vertical speed indicators, etc.), utilizing static pressure.

 

With the movement of the airplane, impact pressure on the open pitot tube affects the pressure within the pitot chamber. Pressure changes inside the pitot chamber are then transmitted through pressure lines connected to the airspeed indicator, which functions with the impact pressure.

 

Aircraft Indicators Configured with Pitot-Static System:

By studying and interpreting the Pitot-static instruments, various indicators are derived as follows. However, sophisticated modern systems use an air data computer (ADC) to calculate the following indicators:

 

 

Pitot-Static System – Errors and Maintenance:

 

Pitot-static errors: Several parameters and situations affect the accuracy of the pitot-static pressure readings, leading to incorrect reading in the instruments. These also involve failures of the pitot-static system, termed “system malfunction,” and others are operational errors due to faulty instrument placement or environmental conditions, termed “inherent errors.” Examples of system malfunction errors are Blocked pitot tubes, leading to erroneous airspeed indicators, and Blocked static ports affecting all pitot-static instruments. Examples of Inherent errors include Position and Lag errors.

 

Maintenance of Pitot-static system: During the pre-flight inspections, vents and openings of the pitot tube and the static must be checked for any obstructions. Blocked or partially blocked vents should be cleaned appropriately by an authorized mechanic. Blowing operations to clean the vents can damage the instruments.

 

Pitot Static Test Sets or Air Data Test Sets:

 

A Pitot static test set consists of the same components or indicators as the Aircraft, such as the Altimeter, Airspeed indicator, Vertical speed indicators, etc. Although test set indicators also use the standard aircraft instruments, modern systems have digital and analog indicators to depict and log the readings. Compared to Pitot-static test sets, digital instruments called Air data test sets (ADTS) are accurate and can be used for testing air data computers and Reduced vertical separation minima (RVSM) equipment. However, the initial cost for ADTS and the maintenance and calibration costs are higher than the Pitot static test sets.

 

Pitot Static Test Sets Calibration – Why is it Essential?

The industry standard for Calibration of Pitot-static test sets and the aircraft indicators is 12 months (annual). However, based on the operational frequency and the mode of operation, test sets need to be calibrated bi-annually to ensure no errors while testing the aircraft indicators. Test sets OEM to provide calibration certificates for the following components:

 

 

Experience informs us that the test set indicators are no more accurate than the existing aircraft systems due to repeated operation and several simulated test conditions. Hence, calibration is necessary for both the test sets and the actual aircraft indicators, and the results are calibrated regularly. The calibration chart can represent the condition of the test set.

 

Air Data Test Sets provide aircraft operators and maintenance organizations with dependable and crucial support.  They are designed to simulate the pressure conditions observed by aircraft during their flights which is required to calibrate the indicators for altimeter, airspeed, manifold pressure, and vertical speed.  It also offers ways of leak monitoring the Pitot-Static mechanism of an aircraft. The accuracy of these parameters is critical for any safe flight.

 

Test readings errors can often result in adjusting the settings of actual aircraft indicators and systems, leading to catastrophic failures, downtime, and maintenance losses. Following a scheduled preventive maintenance and calibration activity, avoid these errors, ensure the fuel quantity system and its components’ accuracy for sustained and repeated use.

 

e2b calibration offers industry-leading ISO-certified pitot-static test set maintenance and calibration services. Calibration of a pitot-static test set is done by comparison to our laboratory standard pressure gauges. Our labs are ISO/IEC 17025 accredited and operated by a team of qualified calibration experts to calibrate your test sets. Our verifiable services are unmatched in the industry. We are registered with ANAB. We are also ANSI/NCSL Z540-1-1994 certified. We have the NIST Traceable Wide scope of ISO/IEC 17025 accreditation. Contact e2b calibration for all your equipment calibration needs.

 

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