Microwave landing system

In an MLS landing system having ground located transmitting means and having MLS airborne receiving and processing means and having a repeating sequence of time intervals for accommodating plural diverse guidance functions which are transmitted in association with data identifying the type of function being transmitted, the possible guidance functions including scanning beam guidance functions comprising scanning beams scanned in first and second directions across a region which an aircraft is approaching for landing and including fixed beam guidance functions paired to overlap within the approach region along a prescribed approach path where their mutual intensities are equal, the method of providing instrument landing guidance within aircraft including the steps of:

• (a) receiving guidance function beams in the aircraft and providing output signals based thereon;
• (b) processing the data associated with the output signals to determine the type of guidance function, as between scanning beam guidance function only, fixed beam guidance function only, and both scanning beam and fixed beam guidance functions;
• and
• (c) processing the output signals appropriately as determined by the data associated therewith, and providing in the aircraft guidance signals which are based upon a single type of guidance function when only one type of guidance function is being transmitted, and which are based upon a comparison of both types of guidance functions when both types of guidance functions are being transmitted.

Apparatus for providing MLS aircraft landing guidance and independently monitoring the accuracy of that guidance for an aircraft approaching along a prescribed path in an approach region, the apparatus transmitting from ground station means to airborne receiver means during repeating sequences of allocated MLS time intervals plural diverse guidance functions respectively including scanning beam guidance functions interspersed with fixed-beam guidance functions, the apparatus comprising:

• (a) at said ground station means, transmitter means selectively connected by radiation control logic means to ground based antenna means and operative for transmitting a scanning beam guidance function in its own time intervals which is radiated into said approach region and including a scanning beam scanning in first and second directions across said approach region, and for transmitting during non-interfering time intervals fixed-beam guidance functions including paired beams directed along opposite sides of the aircraft approach path such that the paired beams overlap said prescribed approach path by the same amount, whereby their beam intensities as measured along the path are mutually equal;
• and
• (b) in said aircraft, receiver means coupled to programmed data processor means connected to landing guidance means, the receiver means being operative to receive signals based on guidance beam functions, and the processor means being operative to process the received signals based on the scanning beam function to provide a first output signal which varies in proportion to the time between the reception of the scanning beam passing in the first and second directions at the present location of the aircraft, and the processor means being operative to process received signals based on the fixed-beam guidance function by comparing their relative amplitudes to provide a second output signal which varies in proportion to the relative strengths of paired fixed-beam signals at the present location of the aircraft, and the processor means being operative to compare the first and second output signals and to deliver to the landing guidance means a guidance signal based on the first output signal when said first and second output signals substantially agree.

In an MLS landing system having multiple differently functioning ground stations for providing landing guidance for an aircraft approaching a station along a prescribed path in an approach region and wherein the ground station transmits diverse aircraft guidance functions to airborne receiver means in a repeating sequence of allocated MLS time intervals and transmits with said guidance functions associated data functions defining the types of guidance functions transmitted at that MLS ground station, improved MLS apparatus wherein:

• (a) the various MLS ground stations comprise transmitter means selectively connected by radiation control logic means to ground based antenna means which are selectively operable for transmitting at least one of diverse precision guidance functions in allocated time intervals in said sequence, which functions include a scanning beam guidance function radiated into said approach region and including a scanning beam scanned in first and second directions across said approach region, and which functions include fixed-beam guidance functions having paired beams directed along opposite sides of the aircraft approach path such that the paired beams overlap said prescribed approach path by the same amount, whereby their beam amplitudes as measured along the path are mutually equal;
• and
• (b) the airborn MLS receiver means include means operative to receive transmitted functions and include programmed data processor means connected to the receiver means and operative in response to received data signals to process received guidance signals in the manner determined by associated data signals;
• the processor means being operative to process precision scanning beam signals to provide output signals which vary in proportion to the time between the passing of the scanning beams in said first and second directions at the present location of the aircraft;
• and the processor means being operative to process paired fixed-beam guidance signals by comparing their relative amplitudes to provide output signals which vary in proportion to the relative strengths of the fixed-beam received signals at the present location of the aircraft, and landing guidance means connected to the processor means and operative to receive a guidance signal based on one of said output signals;
• (c) said processor means delivering to the landing guidance means guidance signals which are based upon a single type of guidance function when only one type of guidance function is being transmitted, and which are based upon a selected one of the guidance signals after a comparison of both types of signals when both types of guidance functions are being transmitted.