1. Method of estimation of the speed of an aircraft relative to the surrounding air, of the angle of attack of the aircraft, and of the angle of sideslip of the aircraft, in a reference frame tied to the aircraft, comprising: estimating an estimated static pressure (PSe) on the basis of measurements of the geographical vertical speed (Vzgeo) of the aircraft, of measurements of the temperature (Tair) of the surrounding air, of reinitializations of the estimated static pressure (PSe), and of a feedback of the said estimated static pressure (PSe), by integration over a vertical path of a hydrostatic equation; estimating a linear combination of a first intermediate variation (δTASa) of the speed of the aircraft relative to the surrounding air, of a first intermediate variation (δAOAa) of the angle of attack of the aircraft and of a first intermediate variation (δSSAa) of the angle of sideslip of the aircraft on the basis of a deviation between a variation (δPSe) of an estimated static pressure (PSe) and a variation (δPSm) of a measured static pressure (PSm), the said linear combination using coefficients calculated on the basis of the laws of local aerodynamic correction (SSEC) dependent on the aircraft, the speed (TAS) of the aircraft relative to the surrounding air, the angle of attack of the aircraft (AOA), and the angle of sideslip of the aircraft (SSA), and further comprising estimating a first indicator of quality (IndQa) of the said linear combination estimated by the estimating the linear combination; estimating a second intermediate variation (δTASb) of the speed of the aircraft relative to the surrounding air, a second intermediate variation (δAOAb) of the angle of attack of the aircraft and a second intermediate variation (δSSAb) of the angle of sideslip of the aircraft, on the basis of inertial measurements, and of a feedback of the estimated speed (TASe) of the aircraft relative to the surrounding air at output, of a feedback of the estimated angle of attack (AOAe) of the aircraft at output, and of a feedback of the estimated angle of sideslip (SSAe) of the aircraft at output, by likening the speed vector of the aircraft relative to the surrounding air to a speed vector of the aircraft relative to an inertial reference frame obtained by integration of the components of a measured acceleration vector (Inertial measurements), corrected for the kinematic effect of the reference frame tied to the aircraft and increased by the gravity projected into the reference frame tied to the aircraft; and consisting in estimating a second indicator of quality (IndQb) of the said second intermediate variations (δTASb, δAOAb, δSSAb); fusing the said second intermediate variation (δTASb) of the speed of the aircraft relative to the surrounding air, second intermediate variation (δAOAb) of the angle of attack of the aircraft, and second intermediate variation (δSSAb) of the angle of sideslip of the aircraft respectively with the said first intermediate variation (δTASa) of the speed of the aircraft relative to the surrounding air, first intermediate variation (δAOAb) of the angle of attack of the aircraft, and first intermediate variation (δSSAb) of the angle of sideslip of the aircraft, by filtering of least squares type weighted by the said first and second indicators of quality (IndQa, IndQb) or by a filtering of Kalman type; and of fusing the said first and second indicators of quality (IndQa, IndQb) into a fused indicator of quality (IndQ) on the basis of the error variance estimated by the said filtering; and performing a temporal integration of the said fusion carried out in the fourth step (4), using reinitializations of the estimated speed of the aircraft relative to the surrounding air, of the estimated angle of attack of the aircraft, and of the estimated angle of sideslip of the aircraft so as to deliver at output an estimated speed (TASe) of the aircraft relative to the surrounding air, an estimated angle of attack (AOAe) of the aircraft, and an estimated angle of sideslip (SSAe) of the aircraft.