DAS

Measurement of indicated airspeed by the DAS sensor

The DAS sensor measures indicated airspeed through the aircraft pitot-static system. It receives total pressure from the pitot tube and static pressure from the static pressure line. The pressure difference acts on the internal measuring mechanism, and the sensor converts this movement into an electrical output signal. This signal corresponds to the current indicated airspeed and is sent further into the recording system. In the SARPP-12DM configuration used on Mi-8 helicopters, the typical calibrated measuring range is 60–400 km/h.

DAS sensor as part of continuous flight-parameter recording

In the SARPP-12DM system, the DAS sensor belongs to the continuous analog-parameter channel. Its output is transmitted to the signal distributor and then recorded by the information storage unit together with other flight parameters. These may include altitude, main rotor speed, engine or control-position parameters and other values depending on aircraft configuration. The airspeed record is important because it allows maintenance personnel and investigators to review the aircraft’s speed profile during flight, approach, landing and abnormal events.

Connection of the DAS sensor to the pitot-static system

The DAS sensor has two pneumatic connections. One port receives total pressure from the pitot tube through a flexible hose line, and the second port receives static pressure into the sealed body cavity. Correct connection of these two lines is essential. If the total and static pressure lines are crossed, leaking, blocked or contaminated, the output signal will not reflect the real indicated airspeed. During maintenance, technicians check hose condition, fitting tightness, cleanliness of pressure lines and the absence of moisture or foreign particles in the pneumatic path.

Electrical output and potentiometric circuit of the DAS sensor

The DAS sensor uses an internal potentiometric element to generate an electrical signal proportional to the measured airspeed. The sensor is powered by a low-voltage supply from the flight recorder system, matching device or power supply unit such as BP-7, depending on the aircraft installation. The output is then read by the SARPP-12DM signal chain. Since this is an analog sensor, the accuracy depends on both the mechanical pressure element and the electrical condition of the potentiometer, connector, wiring and supply voltage.

DAS, DAS-48 and DAS-V modifications

In aircraft maintenance documentation, the sensor may appear under designations such as DAS, DAS-48 or DAS-V. These names refer to airspeed sensor versions used in flight data recording systems such as SARPP-12DM and MSRP-12-96. The exact version must be checked before replacement, because measuring range, calibration, connector wiring or aircraft applicability may differ by modification. For Mi-8 applications with SARPP-12DM, the airspeed range and calibration must match the helicopter recording system and approved aircraft documentation.

Construction and installation of the DAS sensor

The DAS sensor is built in a sealed metal cylindrical housing with pneumatic fittings, an electrical connector and a shock-mounted base. The sealed body protects the internal measuring mechanism and allows static pressure to be applied correctly inside the housing. The sensor is installed in the aircraft equipment area and connected to both the pitot-static lines and electrical recording circuit. During inspection, attention should be paid to the housing, shock mount, connector, pneumatic fittings, sealing condition and calibration status.

Supply and checking of the DAS airspeed sensor

For supply or replacement, the full designation and aircraft recorder system should be specified: DAS sensor for SARPP-12DM, or the required modification such as DAS-V if applicable. The unit should be checked by documentation, electrical parameters, pneumatic tightness and calibration points. For aircraft use, the sensor must correspond to the aircraft’s pitot-static and recording system configuration. A visually clean sensor is not enough for installation; correct output across the calibrated speed range must be confirmed during bench or aircraft-level testing.