Cockpit Voice Recorder — Page 512, Lesson 600

Let's start with the cockpit voice recorder itself — the CVR. This is the unit that records flight deck conversations and sounds, and it's your witness in the cockpit. I want to walk you through its control unit first, because that's where you, as the pilot, actually interact with it. The control unit is mounted on the flight deck, usually in the roof panel. It contains the monitoring and testing circuitry, and it also houses the area microphone. That microphone picks up general flight deck conversations and sounds — not just the radio, but everything spoken in the cockpit and the ambient noises around you. Now, the controls. The first is the AUTO/ON switch. When it's 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. That 5-minute delay is deliberate — it captures the final moments after shutdown, which can be critical in an incident. When you select the ON position, the CVR starts recording immediately, and the switch latches in the ON position. It stays latched until the first engine start, at which point it clicks back to AUTO. So ON forces immediate recording, but AUTO is the normal operating mode. Next is the CVR TEST button. Pressing it activates an extensive set of functional tests that determine the integrity of the system. This uses the BITE facility — that's built-in test equipment. A successful self-test results in a visual 'good' indication, which could be a status deflection needle or a status LED. So you get a clear, visual confirmation that the system is healthy. Then there's the ERASE control. Erasure of the tapes is only possible with the aircraft on the ground, all engines stopped, and the parking brake set. Suitable safety interlocks are installed to prevent inadvertent or airborne tape erasure. Additionally, the erase button must be held depressed for at least 2 seconds before the circuit activates. So even on the ground with the parking brake set, you have to hold it for two full seconds — that's a deliberate safeguard against accidental wiping of the recording. Some CVR control units will incorporate the area microphone as shown in Figure 37.2. So the microphone isn't always separate — it can be built right into the control unit itself. Now, let's look at the European Regulations. These rules apply to commercial air transport aircraft registered in the EU, and they're similar to, but not identical to, the requirements for FDRs — flight data recorders. There are 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 the key thresholds are the registration date, the MTOM of 5700 kg, and the passenger seat count of more than 9. 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. And there's a note about combined units: aircraft less than 5700 kg MTOM may carry a combined CVR/FDR, but if the recorders fitted to aircraft greater than 5700 kg MTOM are combined, they must be fitted with two. So a heavy aircraft can't rely on a single combined unit — it needs two separate recorders. That's the core of the CVR — the control unit, its controls, and the regulatory framework. Let me know if you want to dig into any part of that further.