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Method to assess speech intelligibility of Full Face Quick Donning (FFQDM) Mask

IP.com Disclosure Number: IPCOM000244366D
Publication Date: 2015-Dec-07
Document File: 8 page(s) / 257K

Publishing Venue

The IP.com Prior Art Database

Abstract

The method to assess speech intelligibility of FFQDM is applied to cockpit communication between crew members and with ATC. FFQDM are part of the crew oxygen system and are installed at flight deck.

The idea describes an objective method to determine speech intelligibility of FFQDM. First a theoretical background of an applied standard is given and the adaption to the specific problem of FFQDM intelligibility is described. Perceptions from a test campaign are listed. Eventually a conclusion about the applicability of the methodology is given.

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Method to assess speech intelligibility of Full Face Quick Donning (FFQDM) Mask

The method to assess speech intelligibility of FFQDM is applied to cockpit communication between crew members and with ATC. FFQDM are part of the crew oxygen system and are installed at flight deck.

Following CS25.1447(2)(ii) FFQDM "allows, while in place, the performance of normal communication functions". There is neither advice nor a threshold for "normal communication function" available. When assessing communication performance usually speech quality is focused. Speech quality is subjective and depending on several parameters as clarity, sound, loudness, effort and concentration to hear as well as wearing comfort. Speech quality assessment is perception based.

In addition, testing communication is performed differently. FFQDM suppliers conduct tests inside their production facility. Tests in laboratories are different from tests in aircraft environment - the actual field of operation for FFQDM, where different ambient noise is present. Oxygen flow from the mask's regulator and human breathing creates noise which overlays speech. Depending on the selected mode oxygen flow noise can be present permanently (EMER mode). In demand modes (100% and NORM) breathing noise is created by inhaling.

So far communication testing with FFQDM is performed with only one mask. One person wears the masks and communicates with another person without mask. As speaking and inhalation (what creates breathing noise) is anatomically not possible at the same time the current way of testing shows either breathing noise or speech. But in emergency situation at the flight deck at least two persons wear masks while one person is breathing and the other one speaks simultaneously. Then speech and breathing noise is present simultaneously.

In contrast to speech quality the assessment of speech intelligibility is measurable with objective criteria. Speech intelligibility is defined as degree with which a normal person can understand speech and therefore how well speech is transmitted through a system. The physical parameters of the transmission channel are used to characterize intelligibility of transferred speech signals, such as bandwidth, signal-noise-ratio (SNR), reverberation, echo, clipping, distortion.

The mentioned method to assess FFQDM intelligibility reflects the normal situation of FFQDM use: while wearing the FFQDM one crew member speaks to other crew members or to ATC while the other crew member(s) do not talk but breath and create breathing noise. Thus speech is overlaid by noise permanently, but needs to be intelligible despite of. In addition background noise as flight noise is present. The mentioned method considers the speech signal separated from the noise signal. Thus input data are fully flexible. This means that the described method enables the simulation of different signals and is deployable to all kinds of disturbing noise from FFQDM's design and ambient...