Apparently, you can tell a lot about a race by the way they fly. ''Airplane!'' taught us that much 24 years ago, when Barbara Billingsley helpfully translated a black passenger's ''jive'' into English. Now THERE was a race joke -- so transgressively silly, it ascended into the comic absurd-o-sphere. The makers of Soul Plane figured they'd simply reverse the racial polarity and pack a whole movie full of similar material -- just not as funny. Basic, brazen, and scatologically obsessed, ''Plane'' forgoes any analysis of its essentialist japery, marveling instead at its own familiar naughtiness. The best gags -- and the cheapest -- involve the aircraft itself, a pimped-out microcosm of black stereotypes, from its Escalade-sleek First Class cabin to ''Low Class,'' a flying tenement lined with liquor ads. If you're looking for comic insights beyond the well-documented ass differential between whites and blacks, well, golly, you ought to try another carrier.