The MODIS airborne simulator (MAS), a scanning spectrometer built by Daedalus Enterprises for NASA Goddard Space Flight Center and Ames Research Center, is used for measuring reflected solar and emitted thermal radiation in 50 narrowband channels between 0.55 and 14.3 micrometers . The instrument provides multispectral images of outgoing radiation for purposes of developing and validating algorithms for the remote sensing of cloud, aerosol, water vapor, and surface properties from space. Nineteen of the channels on MAS have corresponding spectral channels on the moderate resolution imaging spectroradiometer (MODIS), an instrument being developed for the Earth Observing system (EOS) to be launched in the late 1990s. Flown aboard NASA's ER-2 aircraft, the MAS has a 2.5 mrad instantaneous field of view and scans perpendicular to the aircraft flight track with an angle of +/- 43 degree(s) about nadir. From a nominal ER-2 altitude of 20 km, images have a spatial resolution of 50 m at nadir and a 37 km swath width. We report on the status of the instrument, discuss recent design changes, and provide comparisons with MODIS. We also summarize MAS calibration work, especially efforts to calibrate those channels with strong water vapor absorption.