Abstract <p>This paper is devoted to problems of intellectual support for the aircraft crew in the situation when, in the process of performing a flight assignment by the crew, there arises a conflict “The stage of the flight task being performed is an immediate threat to its fulfillment.” Onboard intelligent tactical-level systems provide the crew with intelligent support in this situation. They identify an immediate threat among the observed potential threats (fix a collision), recommend to the crew a way to counter this threat (solve the task of operational goal setting that occurs to the crew when a collision occurs), and recommend to the crew the details of this method. One of these systems is presented, implemented in the form of an onboard real-time advisory expert system for the final phases of aircraft landing. Its demonstration sample, adapted to the onboard information environment of the MS-21 aircraft, successfully passed research tests with a professional pilot at the semirealistic simulation test bench “MS-21 Onboard Equipment Set” at the GosNIIAS.</p>