GM1 SPA.NVIS.110(e) Equipment
requirements for NVIS operations
ED Decision 2023/007/R
DEMONSTRATION OF
EQUIVALENT VISUAL ACUITY — SET OF SPECIFICATIONS AND GENERATIONS
(a) When assessing whether different NVG meet the same set of
specifications for the purpose of demonstrating equivalent visual acuity, as
described in point (a)(2)(ii) of AMC1 SPA.NVIS.110(e), generations may be defined as per US military
specifications or using the following criteria:
(1) Generation 0 typically uses an S-1 photocathode with peak
response in the blue-green region (with a photosensitivity of 60 micro A /lm),
electrostatic inversion, and electron acceleration to achieve gain.
Consequently generation 0 tubes are characterised by the presence of geometric
distortion and the need for active infrared illumination.
(2) Generation 1 typically uses an S-20 photocathode (with a
photosensitivity of 180-200 micro A /lm), electrostatic
inversion, and electron acceleration to achieve gain. Because of higher
photo-sensitivity, generation 1 was the first truly passive image intensifier.
Generation 1 is characterised by the presence of geometric distortion, low
performance at low light level and blooming.
(3) Generation 2 typically uses an S-25 photocathode (extended red,
with a photosensitivity of 240 micro A /lm or more), and a
microchannel to achieve gain. Generation 2 tubes provide satisfactory
performance at low light levels and low distortion.
(4) Generation 3 uses gallium-arsenide for the photocathode
(photosensitivity of 800+ micro A /lm in the near infrared) and
a micro-channel plate for gain. The microchannel is coated with an ion barrier
film to increase tube life. Generation 3 has very good to excellent
performance at low light level. Recent models have no perceptible distortion.
(b) NVG of ‘generation 3 autogated’ or ‘generation 3+’ as defined
by the US military are sometimes called ‘generation 4’ commercially. The
differences with generation 3 are limited to the following and are therefore
considered not to be significant. Generations 3 to 4 as mentioned above may be
considered to be the same generation.
(1) they are autogated, therefore more robust to high illumination
and abrupt changes of the illumination level
(2) they are unfilmed, which gives less image noise
(c) A non-civilian set of specifications — other than generations —
that ensures sufficient equivalent visual acuity may also be used. For
example, OMNI specifications from the US military may be used.
(d) The figure of merit is resolution * signal to noise ratio.
[applicable from 25 May 2024
— ED Decision 2023/007/R]
EASA aviation regulations define Night Vision Imaging System (NVIS) equipment requirements, specifically visual acuity. Different NVG generations (0-3) are classified based on photocathode technology and performance. Advanced "autogated" or "3+" NVGs are similar to generation 3. Alternative specifications ensuring equivalent visual acuity, like US military OMNI, are also acceptable.
* Summary by Aviation.Bot - Always consult the original document for the most accurate information.
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