©2019. American Geophysical Union. All Rights Reserved. Drastic variations of radiation-belt/ring current electrons are the result of competing processes of acceleration, transport, and loss. For subrelativistic energetic electrons (10–100 keV), one of the promising loss mechanisms is precipitation into the atmosphere due to pitch angle scattering by whistler mode chorus waves. The efficiency of the scattering has yet to be quantified by direct observations, however. Using in situ measurements by the ERG (Arase) spacecraft in the midnight-to-dawn sector at and around the magnetic equator, we demonstrate that the full filling of energetic electron loss cones occurs commonly, associated with typical-amplitude (greater than 50 pT) chorus waves. The spatial distribution of the loss cone filling indicates that the efficient scattering is limited to |MLAT|< 10°.