The present invention relates generally to the detection of hazardous windshear phenomena and more specifically to the detection and alerting of the flight crew of aircraft of windshear conditions.
Windshear is a weather condition which results in rapidly changing wind velocity and direction. In terms of aircraft flight performance, windshear is, of course, most dangerous during takeoffs and landing approaches. Of the numerous causes of windshear, the microburst has been identified as the most hazardous to aircraft flight. Aircraft accidents have been attributed to microburst.
Microburst consists of a rapidly descending column of air that, when striking the ground, spreads out in a fan-like fashion As the air spreads out from the center of the ground impact area, serious changes in wind occur which can adversely affect an aircraft's ability to remain aloft. Hence, an aircraft may experience a descent toward the ground due to the down-flowing air mass and also a loss in airspeed as it encounters a rapidly changing tailwind due to the outflow.
In the prior art, windshear detection systems have been constructed to detect the presence of windshear by using combinations of ground speed, vertical and horizontal accelerations, airspeed, and other measurements. Such a windshear system is illustrated in U.S. Pat. No. 4,593,285, entitled "Windshear Detection and warning System with Evasion Command", issued June 3, 1986 to H. Miller, et al. This patent is incorporated herein by reference. A deficiency of the disclosed system is that the windshear must be encountered before a warning is given to the flight crew. That is, the systems are reactive in nature. In addition, such systems are unaware of the general atmospheric conditions surrounding the aircraft.
Recent studies have indicated a high correlation between certain atmosphere conditions and the presence of a microburst. Most notable of these has been the correlation between temperature lapse rate and microbursts as described in "The Crash of Delta Flight 191 at Dallas-Fort Worth International Airport on 2 Aug. 1985: Multiscale Analysis of Weather Conditions", NOAA Technical Report ERL-430-ESG 2, F. Caracena et al, Dec. 1986. This last mentioned publication is incorporated herein by reference. Temperature lapse rate is the measurement of the change in ambient temperature with altitude. The just referred to publication describes an aircraft accident attributed to microburst.
By measuring the temperature lapse rate with suitable filtering to eliminate unwanted noise and comparing the computed temperature lapse rate to a value commensurate with unstable air, known as the dry adiabatic temperature lapse rate, it is possible to warn the flight crew of the high probability of microbursts considerably before prior art systems. Hence, it is possible for the flight crew to be warned and thus avoid a microburst condition without the necessity of penetration into the microburst required by prior art warning systems.