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Troubleshooting A Thales Sextant Triple Tachometer Indicator

March 2013

The Thales Sextant Triple Tachometer Indicator is installed on Eurocopter Dauphin helicopters. This tachometer measures turbine and rotor speeds (RPMs) with three pointers powered by three internal motors and associated gear trains. To keep this unit running at peak performance, periodic cleaning is recommended. This is a cost effective alternative to exchanging the indicator. As with most avionics units, proper handling and maintenance are necessary to maintain a working unit. Below are some common squawks associated with the triple tachometer indicator.

Sticky Pointers

With the triple tachometer, the pointers can begin to stick and not come up to speed. Cleaning, using an ultrasonic cleaner, and re-lubrication of the gear trains will usually correct these problems.

Broken Glass

Sometimes normal life in the cockpit can cause some common squawks such as broken glass or damaged pointers. Glass can become cracked when a pilot, co-pilot or other maintenance technician leans against or steps on the glass while working in the cockpit area. Of course, when a unit is mishandled or dropped, a pointer can be easily damaged.


Unfortunately light bulbs won’t last forever. When the backlighting goes out, it may be time to replace a bulb.

Because the tachometer operates at such high speeds, when the unit is opened for maintenance or overhaul, it requires a test set capable of simulating those high speeds. Duncan Aviation has an Ideal Aerosmith, model 1921 Tachometer Tester capable of testing all three pointers at the same time at speeds as high as 10,000 RPMs.

If you have any questions about this or other avionics troubleshooting issues, contact a Duncan Aviation’s Avionics Tech Reps; or to schedule maintenance or overhaul on your Thales Sextant Triple Tachometer Indicator, contact Duncan Aviation’s Avionics/Instruments Customer Account Reps.

Duncan Aviation provides comprehensive avionics and instrument overhaul and repair services, and we are an avionics and instrument authorized service center for many of the top equipment manufacturers. Our capabilities listings are available online in our inventory and capabilities search.