Allied Telesis AT-SBx81CFC960 - Manual (Page 256)

Chapter 12: Replacing Modules
256 Section II: Installing the Chassis
Figure 169. Installing a New AT-SBxFAN12 Fan Module
2. When you feel the fan module make contact with the connector on the
backplane, gently push on the top and bottom of the faceplate to seat
the module on the connector. Refer to Figure 170 on page 257.