Tuesday, November 29, 2011
Identifying Reds in NVG Cockpits
Question:How are reds identified in full NVG cockpits? What are the different reds and how do they differ?
Answer:Red indications and annunciations are, and will always be, an important issue in the world of NVG modifications. The reason being the color Red inherently has a large amount of near infra-red (NIR) radiation within its spectral composition, and as we know, NVGs are extremely sensitive to radiation in the NIR band. Therefore, special consideration must be paid to the presence of and the modification of Reds in the cockpit to ensure that NVG acuity is not degraded to unacceptable levels when the Reds are illuminating during NVG operations.
To better understand the current state of Reds and their variations, lets briefly discuss the history of Reds in the NVG cockpit. The first use of NVGs in the cockpit was by the military and their use became widespread during the 80s. During the 80s, the technology of the NVGs themselves was not up to today's standards and these older NVGs were particularly sensitive to Reds. To address this issue, the military simply wrote a standard (MIL-L-85762) that said Reds did not have to be used in a "Class A" cockpit environment, even for warning annunciations. Instead, NVIS yellow would be used in place of Reds for Warnings and Master Cautions and NVIS Green would be used for everything else. The standard was later updated to allow the limited use of NVIS Red (an orange variation of Red) in "Class B" cockpits for Warnings, however, military NVG cockpits generally avoided the use of Reds so there would not be any NVG in-compatibility issues. Although this design concept was acceptable to the military, there were obvious issues with civilian certification based on the fact that the regulations REQUIRE the use of Reds for warning annunciations and Amber for caution annunciations.
As NVG technology advanced and the demand for civilian NVG operations increased throughout the 90s, the FAA had to address NVG operations and the use of Reds in civilian certified NVG cockpits. The result of the FAA and industry's efforts was a minimum operational performance standards document RTCA/DO-275. This document set the standards for civilian NVG modifications and required that cockpits be modified for "Class B" compatibility and required the use of Class B NVGs that met prescribed performance standards. The idea was that if the higher performance Class B NVGs were used in conjunction with NVIS Red (an orange variation of Red) for warnings and NVIS Yellow in place of Amber for cautions, then the safety requirements for civil certification would be satisfied.
In concept this idea is sound, however, it application there can be issues. The regulations require that Red be used for warnings and that Amber be used for cautions and therefore non-modified civilian aircraft generally follow this requirement. However, variations in what constitutes Red and Amber is present between manufacturers and as a result some discrepancies may be present in baseline aircraft prior to modification. As a modifier, we typically try to retain the OEM color scheme as must as possible during modification while still meeting the RTCA/DO-275 standards, however, there are inevitably situations in which colors must be tweaked in order to provide uniformity in colors throughout the cockpit and to ensure compatibility with a operator's NVGs. In addition, as filtering technology advanced through the 2000s, it has become possible to have NVG compatible Reds that meet the standard aviation definition for Reds, however, some manufacturers still produce NVIS Red components and so modifiers will continue to have issues addressing Red uniformity in the cockpit.
So in the end, from a certification stand point, the following key points must be addressed in order to achieve a civilian approval of Reds in a NVG cockpit:
- The color used for Red must be distinguishable as "Red" compared to all other colors in the cockpits so that there is no confusion between warnings and cautions. For example, if NVIS Red is used, then Amber would not be an acceptable color for cautions due to the similarity between NVIS Red and Amber, instead, NVIS Yellow would need to be used.
- The color used for Red must be uniform throughout the cockpit so that there is no question whether an annunciation is a warning or not. For example, if Red is used, then there should not be other warnings using other shades of Red (orange, pink, NVIS Red, etc.) that could lead to confusion.
- The NVIS radiance output of the Reds must be low enough that the acuity of the NVGs is not degraded to unacceptable levels when the Reds are illuminating during NVG operations.
Jessie K. Kearby is a Certification Engineer for Aircraft Night Vision System Integration, Modification and Repair Center at Aero Dynamix, Inc.
In addition to his established working relationship with the FAA, Jessie K. Kearby was recently recognized by Transport Canada Civil Aviation (TCCA) as a Subject Matter Expert on Aircraft Night Vision System Modification.