Flight Data Recorder — Page 501, Lesson 596

Let’s pick up with the regulatory side of the Flight Data Recorder — the "other requirements" that go beyond the basic recording function. 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 incapable of moving under its own power. In practice, that means it starts when the first engine is started, and it switches off automatically 5 minutes after the last engine is shut down. So the recorder is live for the entire period the aircraft could possibly move — from the moment the first engine fires until five minutes after the last one stops. Next, underwater location. The FDR must have a device to assist in locating it in water. That’s the underwater locator beacon — the acoustic pinger — so the recorder can be found if it ends up in the sea. Now the weight-based rules. Aeroplanes of 5700 kg or less may have the FDR combined with the cockpit voice recorder — a single combined unit. Aircraft above 5700 kg must have 2 recorders — either separate FDR and CVR, or 2 combined recorders. So above that weight, you need two independent recording units. Then there’s the dispatch rule — when you’re allowed to fly with an inoperative FDR. Four conditions must all be met. First, it must not be reasonably practicable to repair or replace the FDR before flight. Second, the aeroplane must not exceed 8 further consecutive flights. Third, not more than 72 hours may have elapsed since the unserviceability. And fourth, any cockpit voice recorder required to be carried must be operative — unless it is combined with the FDR. So if the FDR is unserviceable, you can still dispatch, but only within those tight limits: 8 flights, 72 hours, and a working CVR unless it’s a combined unit. That’s the full set of "other requirements" for the FDR. Now, the next chapter moves on to the Cockpit Voice Recorder — the CVR — which is the companion system. Let’s start there.