Original measurements were obtained in stratocumulus, contrails and cirrus clouds by using a new optical airborne probe, the 'Polar Nephelometer,' which is the first airborne instrument to make direct in situ measurements of the scattering phase function of cloud particles over a broad range of sizes (from a few micrometers to about 500 &mgr;m diameter). Preliminary measurements show that in stratocumulus water droplet cloud, the measured phase function fits very well with the phase function derived from direct PMS probes measurements. This definitively confirms the reliability of the Polar Nephelometer for airborne measurements. In contrails and natural cirrus, measured scattering phase function indicates major differences with those used in cloud models which assume ice spheres or simple geometric shape of ice particles. These results highlight new potential insights on both modelling of climate processes and methodologies for cloud remote sensing from satellite measurements. ¿ 1998 American Geophysical Union