Flight Data Recorder — Page 501, Lesson 596

Let’s pick up with the Flight Data Recorder’s regulatory requirements — the “other requirements” that govern how the FDR must behave and how it may be dispatched. First, the automatic start and stop. The FDR must start recording automatically before the aeroplane is capable of moving under its own power, and it must stop automatically after the aeroplane is no longer capable of moving under its own power. In practice, this is achieved by starting the recorder when the first engine is started, and switching it off automatically 5 minutes after the last engine is shut down. So the trigger is engine state, not the aeroplane actually rolling. Next, the FDR must carry a device to assist in locating the recorder in water — that’s the underwater locator beacon, the acoustic pinger. Now the mass-based rules. Aeroplanes of 5700 kg or less may have the FDR combined with the cockpit voice recorder into a single unit. Aircraft above 5700 kg must have two recorders — either separate FDR and CVR, or two combined recorders. So above that threshold you always end up with two recording devices on board. Then there’s the dispatch rule for an inoperative FDR. An aeroplane may be dispatched with an FDR that is not working, provided four conditions are all met. First, it is not reasonably practicable to repair or replace the FDR before flight. Second, the aeroplane does not exceed 8 further consecutive flights with the fault. Third, not more than 72 hours have elapsed since the unserviceability was identified. And fourth, any cockpit voice recorder required to be carried is operative — unless that CVR is combined with the FDR, in which case the combined unit being inoperative means the CVR is also inoperative, so that condition doesn’t apply. So the key numbers to hold onto: 5700 kg for the combined-unit threshold, 5 minutes after last engine shutdown for the automatic stop, 8 consecutive flights, and 72 hours for the dispatch relief. Now, the next chapter moves to the Cockpit Voice Recorder — the CVR. The chapter opens with an introduction, then covers the recording itself, the voice recorder unit, the control unit, and European regulations. Let’s start with the introduction and the recording. The CVR records cockpit audio — the conversation and sounds in the flight deck. The recording is continuous, and it operates on a loop, so it constantly overwrites the oldest audio with the newest. That’s the key principle: it’s a rolling recording, not a permanent one. The voice recorder itself is the physical unit that captures and stores that audio. And the control unit is the interface on the flight deck — the panel the crew uses to operate the recorder, typically with a test function and an erase function. Now, European regulations govern how the CVR must be installed and used — those are the EASA rules that specify things like recording duration, which channels are recorded, and when the recorder must be running. Let’s go into the recording in more detail. The CVR records multiple audio channels — typically the pilots’ microphones, the cockpit area microphone, and sometimes the public address system. The recording is time-stamped, so investigators can correlate the audio with the flight data recorder parameters. The control unit is the crew interface. It has a test switch to verify the recorder is functioning, and an erase switch to wipe the recording — though in practice, erasure is often inhibited during flight to protect the evidence. European regulations — under EASA, the CVR must record for a minimum duration, typically the last 2 hours of operation, and it must start recording automatically before the aeroplane is capable of moving under its own power, just like the FDR. The regulations also specify that the CVR must be crash-protected — housed in a container that can survive impact, fire, and deep-water immersion. So the CVR and FDR work together: the FDR captures the aircraft’s performance data, and the CVR captures the crew’s conversation and cockpit sounds. Together they give investigators the full picture of what happened on a flight. Let me know if you want to go deeper into any of these — the control unit’s functions, the European regulations in detail, or how the CVR’s crash protection works.