Аннотация:The theory of flute instability is reexamined, and it is shown that the variability of plasma pressure on the surfaces U=const may give rise to new types of flute instabilities. Expressions are obtained which make it possible to determine instability increments for any magnetic field configuration. The increments of flute instabilities for the case of a dipole magnetic field, relevant to the physics of the magnetosphere, are calculated as an example. Numerical estimates of instability increments are also presented for the magnetic field of the earth.