AMC 29.1457 Cockpit Voice Recorders

This AMC provides further guidance and acceptable means of compliance to supplement FAA AC 29-2C § AC 29.1457. § 29.1457, to meet EASA's interpretation of CS 29.1457. As such, it should be used in conjunction with the FAA AC.

1. General

The installation of a recorder with an ETSO authorisation against ETSO-C123c (or equivalent standard accepted by EASA) satisfies the approval requirement in CS 29.1457(a).

In showing compliance with CS 29.1457, the applicant should take into account EUROCAE Document ED 112A ‘MOPS for Crash-Protected Airborne Recorder Systems’ or a later revision.

‘CVR system’ designates the cockpit voice recorder (CVR) and its dedicated equipment (e.g. dedicated sensors or transducers, amplifiers, dedicated data buses, dedicated power source).

2. Automatic means to stop the recording after a crash impact

The automatic means to stop the recording within 10 minutes after a crash impact may rely on:

a. Dedicated crash impact detection sensors. In this case, negative acceleration sensors (also called ‘g-switches’) should not be used as the sole means of detecting a crash impact; or

b. The recording start-and-stop logic, provided that this start-and-stop logic stops the recording 10 ± 1 minutes after the loss of power on all engines.

3. Means for the flight crew to stop the cockpit voice recorder

The means for the flight crew to stop the cockpit voice recorder function after the completion of the flight is needed in order to preserve the recording for the purpose of investigating accidents and serious incidents. In fulfilling this requirement, it is acceptable to use circuit breakers to remove the power to the equipment. Such a means to stop the cockpit voice recorder function is not in contradiction with FAA AC 29-2C, § AC 29.1357, § 29.1357, point b.(6), because it would not be used under normal operating conditions, but only after an accident or a serious incident has occurred.

4. Power sources

The alternate power source is a power source that is different from the source(s) that normally provides (provide) power to the cockpit voice recorder. In CS 29.1457(d)(6), a ‘normal shutdown’ of power to the recorder means a commanded interruption of the power supply from the normal cockpit voice recorder power bus; for example, after the termination of a normal flight. The following applies to the installation of an alternate power source:

a. A tolerance of 1 minute on the 10 minutes minimum power requirement of CS 29.1457(d)(6) is acceptable;

b. The use of helicopter batteries or other power sources is acceptable, provided that electrical power to the essential and critical loads is not compromised;

c. If the alternate power source relies on dedicated stand-alone batteries (such as a recorder independent power supply), then these batteries should be located as close as practicable to the recorder;

d. If the cockpit voice recorder function is combined with other recording functions within the same unit, the alternate power source may also power the other recording functions; and

e. The means for performing a pre-flight check of the recorder for proper operation should include a check of the availability of the alternate power source.

5. Combination recorder

In cases where the recorder performs several recording functions, the means for pre-flight checking of the recorder for proper operation should indicate which recording functions (e.g. FDR, CVR, data-link recording, etc.) have failed.

6. Evaluation of the CVR recording

The following acceptable means of compliance with CS 29.1457(b) is provided to demonstrate that the performance of a new or modified CVR system is acceptable and that the quality of the CVR recording is acceptable. Inspections of the CVR recording that are part of the instructions for continued airworthiness (ICAs) are not within the scope of this paragraph.

a. The CVR system should be installed in accordance with the recommendations made in EUROCAE Document ED-112A, in particular:

— Chapter 2-5 ‘Equipment installation and installed performance’, and

— Part I ‘Cockpit Voice Recorder System’, Chapter I-6.1.1 ‘Interface design’, I-6.1.2 ‘Recorder Operation’ and I-6.1.3 ‘Bulk Erasure Interlocks’.

Particular attention should be given to the location of the cockpit area microphone (CAM).

ED-112A, Chapter I-6.2. ‘Equipment location’, provides guidance on this topic.

It should be noted that the CVR may record on more than four channels, and that this may help to avoid superimposition between signal sources recorded on the same CVR channel.

b. To ensure that the CVR system is properly installed, and to verify that the audio signals recorded on all channels achieve the acceptable level of quality, the applicant should conduct a flight test. The recording obtained should be evaluated to confirm an acceptable level of quality during all normal phases of flight (including taxi-out, hover, take-off, climb, cruise, descent, approach, landing, taxi-in) and autorotation. ED-112A provides guidance for testing a new CVR installation (refer to Chapter I-6.3).

c. The evaluation of the CVR recording should include:

i. the tasks described in ED-112A, Annex I-A, Chapter I-A.3;

ii. checking that the vocal signal sources are intelligible and that non-vocal alerts on headsets or speakers can be identified;

iii. checking that the levels of side tone signals (e.g. radio) and public address (PA) are adjusted so that these signals are audible and do not mask the signals from the flight crew microphones (refer to ED-112A, Part I, Chapter I-6.1.1);

iv. checking the start-and-stop function of the CVR system. The CVR should begin to operate no later than when power from sources other than from the alternate power source is available and the pre-flight checklist is started. The CVR should continue to operate either until the completion of the final post-flight checklist or until 10 minutes after power is lost on all engines; and

v. checking for the presence of any fault in the memory of the built-in test feature of the CVR, if applicable.

d. The evaluation of the CVR recording should fulfil all of the conditions below:

i. The equipment used for the CVR recording replay should meet the specifications of Chapter I-A.2 of Annex I-A of ED-112A, or a higher standard;

ii. The replay and evaluation of CVR recordings should be performed by personnel with adequate knowledge of CVR systems and aircraft operations, and who have the appropriate experience with the techniques used to evaluate recordings;

iii. The observations from the evaluation should be documented in an evaluation report. An example of an evaluation report is provided in ED-112A, Annex I-A; and

iv. The evaluation report should indicate the quality of each audio signal that is required to be recorded by CS 29.1457(c) according to defined criteria. For example, the following audio quality rating scale may be used:

GOOD:

1. When considering a vocal signal source (crew voice, radio reception, radio side tone, interphone, public address, synthetic voice in call-outs, warnings and alerts) recorded on a channel other than the CAM channel, the signal is intelligible without using any signal post-processing techniques, and no significant issue (e.g. saturation, noise, interference, or inadequate signal level of a source) affects the quality of this signal;

2. When considering non-vocal alerts recorded on a channel other than the CAM channel, the sounds are accurately identifiable in the recording without using any signal post-processing techniques, and no significant issue affects the quality of the sound recording;

3. When considering the CAM, the recording is representative of the actual ambient sound, conversations and alerts as if an observer were listening in the cockpit, and no significant issue affects the quality of the signal; and

4. No ‘medium’ or ‘major’ issue is identified on any channel (see Table 1 below for examples).

FAIR: A significant issue affects the signal source being considered. However, the related signal can still be analysed without signal post-processing, or by using signal post-processing techniques provided by standard audio analysis tools (e.g. audio level adjustment, notch filter, etc.). The severity of the identified issues is not rated higher than ‘medium’ (see Table 1 below for examples).

POOR: The signal source being considered is not intelligible or not identifiable, and this cannot be corrected even with the use of signal post-processing techniques. The severity of the identified issues is not necessarily rated as ‘major’; it may also be rated as ‘medium’ depending on the consequence for the required signal sources (see Table 1 below for examples); and

v. the audio quality rating of a CVR channel required by CS 29.1457(c) should be the same as the worst audio quality rating among the signal sources to be recorded on this channel.

e. The performance of the CVR system should be considered acceptable by the applicant only if, for none of the signal sources required by CS 29.1457(c) or by the applicable operating rules, the audio quality of the recording was rated as ‘POOR’. In addition, if the CVR system is part of a new aircraft type, the performance of the CVR system should be considered acceptable by the applicant only if for all of the signal sources required by CS 25.1457(c) and by the applicable operating rules, the quality of the audio recording was rated as ‘GOOD’.

Table 1: Examples of issues affecting a signal source and of the associated severity

*CAM line: microphone+control or preamplifier unit+wiring to the CVR

7. Instructions for continued airworthiness (ICAs)

When developing the ICAs for the CVR system, required by CS 29.1529 and its Appendix A, the applicant should address all failures that may affect the correct functioning of the CVR system or the quality of the recorded audio signals.

Examples of failures (indicative and non-exhaustive list):

— The loss of the recording function or of the acquisition function of the CVR.

— Any communication or audio signal (required by CS 29.1457(c) or by the applicable air operations regulations) is missing, or is recorded with an audio quality that is rated ‘POOR’ (refer to the example of audio quality rating provided in Section 6 of this AMC).

— The failure of a sensor, transducer or amplifier dedicated to the CVR system (e.g. failure of the cockpit area microphone).

— The failure of a means to facilitate the finding of the CVR recording medium after an accident (e.g. an underwater locating device or an emergency locator transmitter attached to the recorder).

— The failure of any power source dedicated to the CVR (e.g. dedicated battery).

— The failure of the start-and-stop function.

— The failure of a means to detect a crash impact (for the purpose of stopping the recording after a crash impact, or for the purpose of deploying the recorder if it is deployable).

[Amdt 29/7]

[Amdt 29/9]