Why would a shark eat a plane?

"Thriller in Manilla!" I can't remember how we worked this out but, the shark would be around 100 metres long and its teeth about 12 ft. In the film they say its cruising speed is 500 knots and when attacking "pray indiscriminately" (which is code for army bases and submarines on purpose) it can speed to 800 knots. Fair enough really, I can believe that, it is called a mega shark after all.

Then, just when i finally had my right eye brow lowered from the astonishment of seeing Bruce Willis aim a car into a helicopter in Die Hard 4, it also turns out a shark can time a jump (yep, sharks can jump) traveling at lets say, 700 knots to take a bite out of an airplane that is at least 10,000-20,000 feet above sea level.

Oh, the film is obviously rubbish.