SPA.NVIS.110 Equipment requirements for NVIS operations

RADIO ALTIMETER

(a)The radio altimeter should:

(1)be of an analogue type display presentation that requires minimal interpretation for both an instantaneous impression of absolute height and rate of change of height;

(2)be positioned to be instantly visible and discernable from each cockpit crew station;

(3)have an integral audio and visual low height warning that operates at a height selectable by the pilot; and

(4)provide unambiguous warning to the crew of radio altimeter failure.

(b)The visual warning should provide:

(1)clear visual warning at each cockpit crew station of height below the pilot-selectable height; and

(2)adequate attention-getting-capability for typical NVIS operations.

(c)The audio warning should:

(1)be unambiguous and readily cancellable;

(2)not extinguish any visual low height warnings when cancelled; and

(3)operate at the same pilot-selectable height as the visual warning.

RADIO ALTIMETER An analogue type display presentation may be, for example, a representation of a dial, ribbon or bar, but not a display that provides numbers only. An analogue type display may be embedded into an electronic flight instrumentation system (EFIS).

DEMONSTRATION OF EQUIVALENT VISUAL ACUITY

(a)When demonstrating the equivalent visual acuity of the required NVG, the operator should ensure that one of the following conditions are met:

(1)all required NVG should be of the same make and model;

(2)the operator ensures that both:

(i)the different NVG meet the same set of specifications (e.g. generation); and

(ii)the lowest figure of merit of the different models is no less than 85 % of the higher figure of merit;

(3)the operator:

(i)analyses the available specifications of the NVG that are considered for compatibility. If, based on the specifications that are available, the different models of NVG appear to be of different generations, they should only be used together on the same flight on a temporary basis, as part of an operator’s upgrade to a better generation of NVG;

(ii)conducts an operational demonstration to assess the differences in visual acuity of the different models of NVG that are considered for compatibility, in accordance with (b) below;

(iii)conducts a risk assessment to determine whether the different models can be used by different crew members on the same flight and under which conditions, in accordance with (c) below.

(b)The operational demonstration referred to in (a)(3)(ii) above should include the following:

(1)Environmental conditions. The operational demonstration should take place in all of the following environmental conditions:

(i)Full moon and moisture < 70 % relative humidity

(ii)At least one lighting condition that is in-between

(iii)No moon (e.g. 5 mlux).

(2)Relevant terrain and lights. The operational demonstration should compare the visual acuity offered by the different NVG for a representative set of terrain and lights under all environmental conditions specified above.

(3)Operational environment.

(i)The operational demonstration may take place on dedicated non-commercial flights, or during commercial operations if the following conditions are met:

(A)On any given flight, all crew members use NVG of the same make and model.

(B)Different models of NVG are used on different flights within the same mission.

(C)The lighting conditions remain the same within the same mission.

(ii)An FSTD should not be used for the operational demonstration.

(4)The operator should define the operational demonstration methodology in the operations manual, and should provide to crew members in charge of the assessment an ‘operational demonstration sheet’, which includes all defined elements to be assessed under all defined light conditions.

(5)Crew members in charge of the assessment should have logged at least 100 NVIS flights or 30 hours’ flight time under NVIS as a pilot-in-command/commander.

(c)The risk assessment referred to in (a)(3)(iii) above should consider the following:

(1)The operator should consider the results of the analysis of the available specifications and the results of the operational demonstration in its risk assessment. The conclusion may be one of the following:

(i)The different models of NVG should not be used together on the same flight;

(ii)The different models of NVG may be used on the same flight with no restrictions;

(iii)The different models of NVG may be used on the same flight with one or more of the following restrictions:

(A)The pilot flying uses the best NVG available;

(B)On dark nights, a briefing is made on the differences. Dark nights could be defined either as less than 1mLux or be defined by the operator based on the assessment results;

(C)Any additional restrictions as defined by the operator.

(2)The risk assessment should consider the interchangeability of the NVG available on board, including any NVG of different makes and models, as well as spare NVG.

(3)The risk assessment may consider the benefits of upgrading the NVG to a better standard.

(i)The duration of the transition to new NVG should be taken into account at operator level.

(ii)If the operator has more than one operating base, it may be possible to equip a given operating base with NVG of the same model, whereas another operating base will have different NVG. In such case the operator should determine the conditions under which the crew changes from one operating base to another.

(iii)If the operator defines that a crew member usually uses the same upgraded model of NVG except when one of these is in maintenance, in which case a previous model is used, the operator may need to define additional restrictions and conditions for the use of the previous model. Such conditions may include a familiarisation on ground during the night or training flight before the spare model is planned to be used in flight.

(d)SOPs. The operator should develop SOPs to comply with any restrictions established in its risk assessment. DEMONSTRATION THAT DIFFERENT NVG ARE OF THE SAME FILTER CLASS

(e)The operator should demonstrate that NVG of different models have the same filter class, in order to ensure that they will not filter out different external lights. This might be possible despite both NVG models being compatible with the helicopter as determined in the flight manual.

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.

MODIFICATION OR MAINTENANCE TO THE HELICOPTER It is important that the operator reviews and considers all modifications or maintenance to the helicopter with regard to the NVIS airworthiness approval. Special emphasis needs to be paid to modification and maintenance of equipment such as light emitting or reflecting devices, transparencies and avionics equipment, as the function of this equipment may interfere with the NVGs.