Cockpit Voice Recorder — Page 512, Lesson 600

Let’s start with the Cockpit Voice Recorder, or CVR. This is the unit that captures the flight deck’s audio environment — the conversations, the sounds, the radio calls — so that after an event, investigators can reconstruct what was said and heard in the cockpit. First, the Control Unit. This is the physical panel you interact with on the flight deck. It’s mounted in the roof panel, typically overhead. Inside it, you have the monitoring and testing circuitry, and it also houses the area microphone. That microphone is what picks up the general flight deck conversations and ambient sounds — not just the radio, but the actual voices and noises in the cockpit. Now, the controls on that unit. There’s the AUTO / ON switch. In the AUTO position, the CVR starts recording when the first engine is started, and it stops recording 5 minutes after the last engine is shut down. So it’s tied to engine operation. If you select ON, the CVR starts recording immediately, and the switch latches in the ON position — meaning it stays there — until the first engine start, at which point it clicks back to AUTO. So ON forces immediate recording, but once the engines are running, it reverts to the automatic mode. Next, the CVR TEST button. Pressing it activates an extensive set of functional tests. These tests determine the integrity of the system using the BITE facility — that’s built-in test equipment. So the unit runs a self-check. If the self-test is successful, you get a visual ‘good’ indication — either a status deflection needle or a status LED. That’s your confirmation the system is healthy. Then there’s the ERASE control. Erasure of the tapes is only possible under very specific conditions: the aircraft must be on the ground, all engines stopped, and the parking brake set. There are safety interlocks installed to prevent inadvertent or airborne erasure — so you can’t accidentally wipe the tape, and you can’t do it while flying. Additionally, the erase button must be held depressed for at least 2 seconds before the circuit activates. So it’s a deliberate, guarded action. Some CVR control units incorporate the area microphone directly into the control unit itself, as shown in Figure 37.2. Now, the European Regulations. These rules apply to commercial air transport aircraft registered in the EU. They’re similar to, but not identical to, the requirements for Flight Data Recorders — the FDRs. Let me walk you through the three cases. Case 1: All aeroplanes registered after 1 April 1998 which are greater than 5700 kg MTOM — that’s Maximum Take-Off Mass — or turbine powered, less than 5700 kg but with more than 9 passenger seats. Case 2: Turbine powered aeroplanes registered between 1 January 1990 and 31 March 1998, less than 5700 kg MTOM but with more than 9 passenger seats. Case 3: All aeroplanes with MTOM greater than 5700 kg. So those are the categories of aircraft that must carry a CVR. Now, the minimum recording time. It’s 30 minutes, except for aircraft greater than 5700 kg MTOM registered after 1 April 1998, where the minimum recording time is 2 hours. So the newer, heavier aircraft need a longer recording duration. Finally, the rules for despatch with an unserviceable CVR are the same as for an unserviceable FDR. That means if the CVR is not working, you follow the same dispatch rules as you would for a faulty Flight Data Recorder. And one more point: aircraft less than 5700 kg MTOM may carry a combined CVR/FDR — a single unit that does both jobs. But if the recorders fitted to aircraft greater than 5700 kg MTOM are combined, they must be fitted with two. So for the heavier aircraft, you can’t rely on just one combined unit; you need two of them. That covers the CVR control unit, its controls, and the European regulatory requirements. Let me know if you want to dig into any part of that further.