A method of processing a plurality of replies of target aircraft provided in response to interrogation signals from the surveillance aircraft during surveillance periods to determine whether an altitude track may be initialized for use in a traffic alert and collision avoidance system includes the step of selecting three replies, one from each of three consecutive surveillance periods. The replies have binary or coded altitude data of high or low confidence. The binary or coded altitude data of non-adjacent and adjacent replies of the selected replies are compared and an altitude difference value for each of the comparisons is generated. Further efforts to initialize a track are discarded if any of the altitude difference values are greater than first predetermined separated altitudes if and only if such compared non-adjacent and adjacent replies have binary or coded altitude data of high confidence. The binary or coded altitude data of the non-adjacent and adjacent replies are further compared whether or not the replies have binary data of low or high confidence to determine whether an altitude track may be initialized. The process applies if the altitude data is Gilham code, binary, or other encoded data with single bit errors.

In a method of communicating data between a transmission/reception center and a target, a transaction is constituted by one or more interrogation pulses sent out by the center followed by one or more associated reception windows designed to receive the response from the target that has been sent the associated interrogation pulse. The length of a transaction is the delay between its interrogation pulse and its reception window, the transactions are classified and positioned according to their distances from the radar in decreasing order. The reception window of each transaction is transmitted immediately before the window of the immediately lower-ranking transaction so long as its associated pulse does not overlap an interrogation pulse of a transaction. If the contrary is the case, the transaction is shifted within the previously-transmitted transactions until it no longer overlaps an interrogation pulse or a reception window of these previously-transmitted transactions, the transaction being transmitted after all the previously-transmitted windows if a place without overlapping is not found in this way.

A method for inhibiting responses by transponders to interrogation signals originating in the side lobes of an interrogating radar of a secondary radar system. The interrogating radar first transmits a reference signal with the highest power level of the reference signal being directed into a zone of interest to the interrogating radar. The interrogating radar then transmits a control signal having a higher power level than the reference signal in all regions of space except within the zone of interest. The control signal is of substantially longer duration than the reference signal. A transponder receives, detects and measures the peak amplitude of the reference signal and establishes a minimum trigger level (MTL) at a predetermined level below the reference signal peak. The control signal is received, detected and integrated. The peak amplitude of the integrated control signal is compared with the MTL. A transponder response is inhibited if the peak amplitude of the integrated control signal is greater than the MTL. The peak amplitude of the integrated control signal may be amplified before comparison with the MTL to increase the amount of synthetic beam sharpening provided by the method and the amount of synthetic beam sharpening provided may be controlled by the interrogating radar by delaying the start of transmission of the control signal.

An integrity monitor for TCAS mutual suppression checks the interface circuits and cabling of the suppression system that lies between the TCAS processor and the transponder. The monitor starts by interrogating the transponder while disabling suppression. If no reply is received, the transponder is not functional. If a reply is received, interrogation of the transponder occurs again, however, this time suppression is enabled. If a reply is received, the suppression system has failed and TCAS alarms will be inhibited. If a reply is not received, the suppression system is working.

An aircraft system and method for determining when to attempt acquisition of an intruder for active tracking. A link reliability score associated with the intruder is adjusted based upon the signal strength of transmissions, the frequency of the transmissions, and the number of previous attempts to acquire the intruder for active tracking.