The FAA warned aircraft operators to reconsider their assumptions, such as the typical 15-percent safety margin, used to calculate turbojet-stopping distances on wet runways, according to a new Safety Alert for Operators (SAFO)—SAFO 15009—that was published late last week. Its analysis of stopping data in a number of landing overrun accidents indicates that the braking coefficients of friction were significantly lower than expected for a wet runway as defined by FAR 25.109 and Advisory Circular 25-7C.

Wet runway landing overruns typically involve multiple contributing factors such as a long touchdown, improper use of deceleration devices, tailwind and less available friction than expected. Measurable incidents have occurred on grooved, non-grooved and non-porous friction course overlay surfaces. The root cause for this wet-runway performance shortfall is not fully understood, although contributors appear to be tied to runway texture, drainage, puddling in wheel tracks and active precipitation.

Agency analysis indicates a more conservative 30- to 40-percent additional stopping distance may be required in cases where the runway is very wet but not flooded. Braking even on grooved or porous friction course runways should be considered as degraded when the runway is very wet.