A method and device for monitoring the validity of a parameter calculated by an anemometric unit of an aircraft may employ a first section for taking into account n first data, each dependent on the parameter being monitored and n being greater than or equal to 1. A second section takes into account p second data that each depends on a value obtained from a data source external to the anemometric unit, where P is greater than or equal to 2. A calculator calculates, for each of the second data, a difference between this second datum and a first datum of the same type. A comparator compares the absolute value of each of the calculated differences with a threshold value. A deducing section deduces from the comparisons that the monitored parameter is invalid if the absolute values of two of the various differences are greater than the corresponding threshold values.

A device for measuring air turbulence in the surroundings of an aircraft includes a measurement system having lidars which are mounted on the aircraft and which are intended to carry out, during a flight of the aircraft, twelve measurements of aerodynamic velocity in the environment surrounding the aircraft. The measurement system carries out the twelve measurements at four different measurement points, each time according to three predetermined axes. A central unit which, with the aid of the aerodynamic velocity measurements and of a first order predetermined mathematical model describing an aerodynamic velocity field as a function of twelve variables, determines an aerodynamic velocity field which exists in the environment of the aircraft and which is representative of the air turbulence.

A measurement system for an aircraft having the three-axis components of the airspeed of the aircraft, the three-axis components of the wind speed currently encountered by the aircraft, and the wind speed distribution ahead of the aircraft simultaneously in real time. It comprises a Doppler anemometer measuring the airflow speeds at a plurality of points separated by a prescribed distance in the beam irradiation direction that changes in a time series, and an inertial data measurement device measuring the movement information and positional information of the aircraft. Moreover, the display system of the aircraft includes the horizontal two-axis airspeed of the aircraft, the three-axis components of the wind speed currently encountered by the aircraft, and information on the wind speed distribution ahead of the aircraft are displayed simultaneously in real time.

An apparatus for use in an aircraft for determining and displaying a reading which is indicative of pressure density at any instant in time, comprises sensing means for determining both ambient air pressure and ambient air temperature at any instant in time, and outputting an electrical signal having a value which varies in accordance therewith. Calculating means are provided for combining those electrical signals and outputting a weighted signal for pressure density having a value based on an index value of zero for a pressure density at sea level when the ambient temperature is 59.degree. F. and the ambient pressure is 29.92 inches of mercury. A microprocessor computer means has random access memory and read only memory, and an output signal driver for outputting a signal indicative of pressure density at any instant in time to a display. The microprocessor includes a lookup and comparator means, and the read only memory contains a plurality of calculated values of pressure density over a range of barometric pressure values. The weighted signal from the calculating means is read by the lookup and comparator means, and compared with values of pressure density stored in the read only memory, so as to determine the value of pressure density at that instant in time, and to display that value. The apparatus will also provide a real time indication of chosen aircraft flying characteristics, depending on the parameters selected, from further lookup tables included in the read only memory.