Well, we are looking not at a passenger jet basically designed to operate in clean air, but a fire-fighting aircraft thatīs very probably designed for the smoky environment itīs beeing operated in. I am thinking of special design considerations for the engines that might keep many particles away from the hot section, maybe air filters for cooling systems, for the pilotsī air... Smoke from forest fires must certainly contain a portion of dust... So, Iīd say that the aircraft is just doing itīs job, should be ok - until the evening inspection. Iīd guess that the engines of these aircraft donīt stay on the wing for 10.000 hr or more even with normal use. A whiff of volcanic cloud ? Well, maybe an engine change is needed earlier than expected, but thatīs for the experts...