Thirteen commerical wing panels were fabricated and flown on a commercial aircraft to investigate the mechanisms of water migration through various honeycomb cores. A 12.2 J impact damage was not observed to cause damage propagation in aluminum and Korex(R) honeycomb materials. This was attributed to the ability of the cores to localize the impact damage. In Nomex(R) and glass fiber cores a different damage propagation mechanism was observed. In these cores, the damage was not confined to the localized area around the impact. Instead, core damage was seen as far as 2.0 cm from the point of impact. This increased core damage allowed the core to retain water. The retained water helped propagate the impact damage through a freeze thaw mechanism. Speed-tape repairs were only found to be statistically significant when water migrated through the core. Filling the honeycomb core with foam was shown to be an effective method for minimizing the damaging effects of water ingression. Slotting and draining the core also offered some relief from water accumulation in the core, but foaming damaged core was established as the most effective technique. (C) 2003 Kluwer Academic Publishers.