An Air Vehicle Navigation System comprising: at least one microcontroller unit and at least one radio receiver unit both located onboard an air vehicle (102, 504, 604), wherein the at least one microcontroller unit is configured for receiving, via the at least one radio receiver unit, instructions for flying the air vehicle (102, 504, 604) towards points in a flying field where atmospheric thermal activity is located; at least one control station at a predetermined distance from the air vehicle, the at least one control station being configured to: generate a grid pattern on a terrain map (128, 400, 500, 600, 700), the grid pattern comprising grid locations (402, 502, 602) representing points in the flying field where the air vehicle (102, 504, 604) flies; associate a determined score to each grid location (402, 502, 602) according to thermals located in the points in the flying field represented by the grid locations (402, 502, 602), wherein the score is allocated based at least on a probability of finding thermals in the point of the flying field represented by each grid location (402, 502, 602), wherein the probability is assigned considering terrain elements on the terrain map (128, 400, 500, 600, 700); send to the at least one microcontroller unit, via the at least one radio receiver unit, instructions to fly the air vehicle (102, 504, 604) towards points in the flying field where atmospheric thermal activity is located according to the score assigned to the grid locations (402, 502, 602) of the terrain map (128, 400, 500, 600, 700). at least one microcontroller unit and at least one radio receiver unit both located onboard an air vehicle (102, 504, 604), wherein the at least one microcontroller unit is configured for receiving, via the at least one radio receiver unit, instructions for flying the air vehicle (102, 504, 604) towards points in a flying field where atmospheric thermal activity is located; at least one control station at a predetermined distance from the air vehicle, the at least one control station being configured to: generate a grid pattern on a terrain map (128, 400, 500, 600, 700), the grid pattern comprising grid locations (402, 502, 602) representing points in the flying field where the air vehicle (102, 504, 604) flies; associate a determined score to each grid location (402, 502, 602) according to thermals located in the points in the flying field represented by the grid locations (402, 502, 602), wherein the score is allocated based at least on a probability of finding thermals in the point of the flying field represented by each grid location (402, 502, 602), wherein the probability is assigned considering terrain elements on the terrain map (128, 400, 500, 600, 700); send to the at least one microcontroller unit, via the at least one radio receiver unit, instructions to fly the air vehicle (102, 504, 604) towards points in the flying field where atmospheric thermal activity is located according to the score assigned to the grid locations (402, 502, 602) of the terrain map (128, 400, 500, 600, 700). generate a grid pattern on a terrain map (128, 400, 500, 600, 700), the grid pattern comprising grid locations (402, 502, 602) representing points in the flying field where the air vehicle (102, 504, 604) flies; associate a determined score to each grid location (402, 502, 602) according to thermals located in the points in the flying field represented by the grid locations (402, 502, 602), wherein the score is allocated based at least on a probability of finding thermals in the point of the flying field represented by each grid location (402, 502, 602), wherein the probability is assigned considering terrain elements on the terrain map (128, 400, 500, 600, 700); send to the at least one microcontroller unit, via the at least one radio receiver unit, instructions to fly the air vehicle (102, 504, 604) towards points in the flying field where atmospheric thermal activity is located according to the score assigned to the grid locations (402, 502, 602) of the terrain map (128, 400, 500, 600, 700).