The Advanced Particle-astrophysics Telescope (APT) is a proposed space-based gamma- and cosmic-ray instrument. The design incorporates a novel dispersed imaging calorimeter constructed from CsI:Na scintillator crystals read out by wavelength shifting (WLS) fibers with scintillating optical fiber tracking layers. A prototype of the CsI:Na calorimeter layer — APTlite — was flown with SuperTIGER during the 2019 austral balloon season in McMurdo, Antarctica. Using SuperTIGER’s trigger system, APTlite captured coincident cosmic-ray events in order to characterize the calorimeter’s performance as a cosmic-ray instrument. Results from this balloon flight will be will be reported including instrument charge and energy resolution.