Patent ID: 6216064
Filing Date: 2001-04-10
Classification: G01C,G01S

Abstract:
A method for determining a modified aircraft altitude signal, said method comprising:a. receiving an air temperature signal, a pressure altitude signal, a first validity signal associated with the pressure altitude signal, aircraft altitude and position signals, and an error signal and a second validity signal associated with the aircraft altitude and position signals;b. if the aircraft is below a predefined altitude, receiving a radio altimeter generated altitude signal and a third validity signal associated with the radio altimeter altitude signal;c. generating a hydrostatic altitude signal based on the received pressure altitude signal and the air temperature signal;d. correcting the received barometric altimeter signal based on the received air temperature signal and a flight crew setting;e. initializing the hydrostatic altitude signal;f. calculating an error signal for the corrected barometric altimeter signal based on a predefined basic error factor, a predefined atmosphere instability factor and a predefined airport database;g. calculating an error signal for the received hydrostatic altitude signal based the initialization of the hydrostatic altitude signal;h. calibrating the hydrostatic altitude signal based on the received aircraft altitude signal, the at least one error signal associated with the aircraft altitude signal and the calculated error signal for the hydrostatic altitude signal;i. if the aircraft is below a predefined altitude, calibrating the hydrostatic altitude signal based on the received radio altimeter generated altitude signal and a predefined terrain elevation database;j. calculating an error signal for the aircraft altitude calibrated hydrostatic altitude signal based on the most recent calibration of the hydrostatic altitude signal and calculating an error signal for the radio altimeter calibrated hydrostatic altitude signal based on the most recent radio altimeter calibration of the hydrostatic altitude signal;k. determining a fourth validity of the aircraft altitude calibrated hydrostatic altitude signal based on said first received validity signal of the received pressure altitude signal and said second validity signal associated with the received aircraft altitude signal and determining a fifth validity of the radio altimeter calibrated hydrostatic altitude signal based on said first validity signal of the received pressure altitude signal;l. determining reasonableness of the generated hydrostatic altitude signal, the aircraft altitude calibrated hydrostatic altitude signal, the radio altimeter calibrated hydrostatic altitude signal and the corrected barometric altimeter signal; andm. generating a modified aircraft altitude signal based on the reasonableness determinations, the fourth and fifth validity determinations, the first, second, and third received validity signals, the aircraft altitude signal, the calculated and received error signals, the generated hydrostatic altitude signal, the aircraft altitude calibrated hydrostatic altitude signal, the radio altimeter calibrated hydrostatic altitude signal and the corrected barometric altimeter signal.