DSL-40T

DSL-40T sensor in the SO-121VM icing system

The DSL-40T is an aircraft ice detection sensor used as the external sensing element of the SO-121VM icing detection system. It is mounted outside the aircraft fuselage, where it is exposed to the same airflow and icing conditions that affect the aircraft during flight or ground operation. The sensor does not work as a standalone warning device. Its task is to detect ice formation on its sensitive membrane and send the resulting signal to the electronic converter, where the signal is processed and used by the aircraft warning or anti-icing logic.

How the DSL-40T detects ice formation

The DSL-40T operates by monitoring the resonant vibration of its membrane element. In clean conditions, the membrane vibrates at its normal resonant frequency. When ice begins to form on the membrane surface, the added mass changes the vibration behavior. This change is detected and converted into an electrical signal for further processing. The principle is practical for aircraft use because it reacts directly to actual ice accretion on the sensor, rather than only estimating icing from temperature or humidity conditions.

DSL-40T as the external sensor of SO-121VM

In the SO-121VM system, the DSL-40T works together with the PE-11M electronic converter and the RM-5 mounting frame. The sensor is the part exposed to the outside airflow, while the converter is installed inside the aircraft and handles signal processing. This separation is important: the sensitive element must be placed where icing can occur, but the electronics need a protected installation area. Depending on the aircraft type, the DSL-40T may be installed on the left or right side of the cockpit area or another approved external fuselage location.

Heating and stable operation of the DSL-40T sensor

The DSL-40T includes an integrated heating element. Heating is needed so that the sensor can operate correctly and restore its sensitive surface after detecting icing. Without proper heating, the membrane could remain covered with ice and the system would not return to a ready state in the expected way. For this reason, the serviceability of the heating circuit is checked together with the sensor signal circuit. A visually intact sensor may still be unsuitable if the heating element, wiring, connector, or insulation condition is not within the required limits.

Aircraft application of the DSL-40T detector

The DSL-40T is used on aircraft and helicopters equipped with SO-121VM icing detection systems. It supports crew warning, anti-icing control, and flight data recording functions, depending on the aircraft configuration. The sensor is relevant for helicopters such as Mi-8, Ka-32 and Mi-26, as well as fixed-wing aircraft including An-38, An-74 and Il-96-300 when fitted with the corresponding system. Before replacement, the sensor location, wiring, connector arrangement and compatibility with the installed converter must be verified against aircraft documentation.

Inspection and replacement of DSL-40T

During maintenance, the DSL-40T should be inspected as an external sensor working in a harsh environment. The membrane area, body, connector, mounting condition, sealing and wiring approach all matter. Contamination, mechanical damage, incorrect clearance, poor heating, or unstable contact can affect detection accuracy. When ordering the sensor, the full designation should be stated in both common forms if needed: DSL-40T and ДСЛ-40Т. It should also be clarified whether the requirement is for the sensor only or for a complete SO-121VM set including PE-11M and RM-5.

Product Type: Aircraft icing detection sensor
Designation: DSL-40T / ДСЛ-40Т
Function: Detection of ice accretion and generation of a signal for further processing
Application / Where Used: SO-121VM aircraft icing detection systems
System / Installation Area: External fuselage mounting, typically in the cockpit area depending on aircraft type
Role in System: Primary external sensing element of the SO-121VM system
Associated System Components: PE-11M electronic converter, RM-5 mounting frame
Working Principle: Change in resonant vibration of the membrane sensor when ice forms
Resonant Frequency: 5950 Hz +35 / −70 Hz
Excitation Current: 20 mA AC
Output Voltage at Resonance: Not less than 150 mV
Output Voltage in Non-Resonant Mode: Not more than ±50 mV
Membrane Heating: Integrated heating element
Mechanical Clearance: 0.2 +0.1 / −0.15 mm
Compatible Aircraft / Equipment: Aircraft and helicopters fitted with SO-121VM, including Mi-8, Ka-32, An-38, An-74, Il-96-300 and Mi-26 depending on configuration
Weight: Not more than 0.55 kg
Technical Documentation: DSL-40T technical documentation, SO-121VM documentation, aircraft maintenance documentation as applicable

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