• Mode A, Code 7500, to indicate specifically that it is being subjected to… — Page 484, Lesson 648

Let's pick this up right where the emergency codes leave off. We're now looking at the specific case of unlawful interference — that's the formal term for hijacking or any forcible interference with an aircraft in flight. First, the key code: Mode A, Code 7500. This is the specific SSR transponder code that a pilot selects to indicate, and I want you to remember this exact phrasing, that the aircraft "is being subjected to unlawful interference." So 7500 is the hijack code. It's distinct from 7700, which is the general emergency code. We'll come back to that distinction in a moment. Now, the priority rule. An aircraft that is known or believed to be in a state of emergency — and this explicitly includes being subjected to unlawful interference — shall be given priority over other aircraft. That's a mandatory requirement, not a suggestion. When you're controlling, that aircraft moves to the front of the queue, period. Next, the responsibility of air traffic services personnel. The regulation says ATS personnel shall be prepared to recognize any indication of the occurrence of unlawful interference with an aircraft. So you're not just passively watching a screen — you're actively looking for the signs that something is wrong. Now here's a critical procedural point — the verification of special SSR codes. This is what the radar controller does when they suspect unlawful interference but aren't sure. The situation: you suspect interference, and your radar display does not automatically show a distinct display of Mode A Code 7500 or Code 7700. In that case, the radar controller shall attempt to verify the suspicion by setting the SSR decoder first to Mode A Code 7500, and thereafter to Code 7700. Note the sequence — 7500 first, then 7700. That's the order of verification. Now, why those two codes? Let me be precise about the expected behavior of the aircraft. An aircraft equipped with an SSR transponder is expected to operate the transponder on Mode A Code 7500 to indicate specifically that it is the subject of unlawful interference. That's the primary hijack indication. However — and this is the important contrast — the aircraft may operate the transponder on Mode A Code 7700 to indicate that it is "threatened by grave and imminent danger, and requires immediate assistance." So 7700 is the general distress code — grave and imminent danger, needing immediate help. 7500 is the specific unlawful-interference code. The pilot uses 7500 when the threat is hijacking; 7700 when the danger is grave and imminent and they need immediate assistance. Then we have the ATC response — what the ATS units must actually do once unlawful interference is known or suspected. First, they shall promptly attend to requests by, or to anticipated needs of, the aircraft. Notice the phrase "anticipated needs" — you don't wait for the pilot to ask; you think ahead. This includes requests for relevant information relating to air navigation facilities, procedures, and services along the route of flight, and at any aerodrome of intended landing. And they shall take such action as is necessary to expedite the conduct of all phases of the flight — meaning you smooth the path for that aircraft through every phase, from departure to landing. Then there are two specific additional duties. First: transmit, and continue to transmit, information pertinent to the safe conduct of the flight, without expecting a reply from the aircraft. That's a key point — you keep broadcasting the safety-critical information, but you do not expect an answer. The crew may be unable to respond, perhaps because a hijacker is in the cockpit. So you transmit one-way, continuously. Second: monitor and plot the progress of the flight with the means available. You track that aircraft on your radar, you plot its position, using whatever equipment you have. You keep eyes on it. So let me tie the whole picture together. You have three distinct codes in play: 7500 for unlawful interference specifically, 7700 for grave and imminent danger requiring immediate assistance, and the verification procedure where the controller checks 7500 first, then 7700. And once interference is known or suspected, the ATS unit gives priority, anticipates the aircraft's needs, transmits safety information without expecting a reply, and monitors and plots the flight's progress. That's the complete unlawful-interference response package.