I do have a maintenance manual that I found on Internet, but it doesn't have anything about the wheel speed transducer.

Any pics along with the information would be helpful.


1 Answer 1


From this Aviation Studies project report of group 2A2I at the University of applied Sciences in Amsterdam, for a Boeing 777-200:

Every wheel is equipped with an anti-skid transducer (appendix VII), which is installed in the axle. The transducer consists of a rotor and stator. According to the speed of rotation, an electrical signal is send to the BSCU.

This computer compares the rotation speed of all the wheels and detects when a wheel is rotating slower than the other wheels on the MLG. The BSCU will send a signal to reduce braking power when the rotation speed of one wheel reduces more in comparison to other wheels.

The principle is the wheel axle drives a permanent magnet within a 3-phase winding. The frequency of the signal generated is proportional to the wheel angular speed.

From B777 General Familiarization Manual:

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Antiskid and Autobrake Diagram, source

Note: I initially believed the tacho-generator was a Socitec ST80, the same than on A320 (part number is C20105000). However when I wanted to provide a supporting document, I couldn't. So please take this as an assumption only until someone provides the part number from a Boeing document (I don't think there would be a big difference between B777 and A320 tacho-generator anyway).

enter image description here
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Tacho-generator, part C20105000, source

More information: Bodet Aero. According to Bodet Aero, their tachometer equips A300, A310, A319, A320, A321, A330 and A340.

More about tachometers: TheAirlinePilots (section "Three Phase AC Electrical Tachometer").

This is a typical installation of the transducer (not a particular aircraft):

enter image description here

  • $\begingroup$ I know how a tachogeneartor operates and thought B777 uses one too but my supervisor said Tachogenerators aren't used in any latest aircraft, they use an auto transformer to do the same. $\endgroup$
    – Pritam
    Nov 10, 2017 at 0:01
  • $\begingroup$ An additional search shows that these transducers are made by Crane/Hydro-Aire, and have part nr 140-025-1, 140-025-2, 140-025100 and 140-025101. But no details on the technology used. $\endgroup$
    – mins
    Nov 10, 2017 at 0:30

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