Appendix 7 – Weather Displays

ED Decision 2015/019/R

1.      Introduction

1.1     Purpose

This Appendix provides additional guidance for displaying weather information in the flight deck. Weather displays provide flight crew with additional tools to help make decisions based on weather information.

1.2     Examples

Sources of weather information may include but are not limited to on-board weather sensors, data-linked weather information, and pilot/air traffic reports. The information from these sources can be displayed in a variety of graphical or text formats. Because many sources of weather information exist, it is important that the applicant identify the source of the information, assess its intended function, and apply the guidance contained within this AMC.

2.0     Key characteristics

In addition to the general guidelines provided in the body of this AMC, the following guidelines should be considered when establishing the intended functions of weather displays.

2.1     Unambiguous meanings

The meaning of the presentations (e.g. display format, colours, labels, data formats, and interaction with other display parameters) should be clear and unambiguous. The flight crew should not misunderstand or misinterpret the weather information.

2.2     Colour

2.2.1  The use of colour should be appropriate to its task and use.

2.2.2  The use of colour must not adversely affect or degrade the attention-getting qualities of the information as required by CS 25.1322(f).

2.2.3  Colour conventions should be followed (such as the conventions established in ARINC 708A-3, Airborne Weather Radar with Forward Looking Windshield Detection Capability, and the FAA AC 20-149A, Installation Guidance for Domestic Flight Information Services-Broadcast).

2.2.4  The use of red and yellow must be in compliance with CS 25.1322(e) for flight crew alerts, or with CS 25.1322(f) for information other than flight crew alerts. Compliance can be demonstrated by using the guidance in AMC 25.1322, Flight Crew Alerting, and this AMC.

Note 1: The FAA AC 20-149A indicates an exclusion to the acceptability of RTCA/DO-267A, Minimum Aviation System Performance Standards (MASPS) for Flight Information Services-Broadcast (FIS-B) Data Link, Sections 2.0 and 3.0, for Part 25/CS-25 aeroplanes.

Note 2: Refer to paragraph 31.c(5) in Chapter 5 of this AMC for information on guidelines on colour progression.

2.3     Multiple sources of weather information

2.3.1  The weather display should enable the flight crew to quickly, accurately, and consistently differentiate among sources of the displayed weather information. Time-critical information should be immediately distinguishable from dated, non-time-critical information.

2.3.2  If more than one source of weather information is available, the source of the weather information should be indicated on the selector and the resulting display.

2.3.3  When simultaneously displaying information from multiple weather sources (e.g. weather radar and data link weather), the display should clearly and unambiguously indicate the source of that information. In other words, the flight crew should know the source of the symbol and whether it is coming from data-linked weather or real-time weather sources. These guidelines also apply to symbols (e.g. winds aloft and lightning) that have the same meaning but originate from different weather information sources.

2.3.4  If weather information is overlaid on an existing display, it should be easily distinguished from the existing display. It also should be consistent with the information it overlays in terms of position, orientation, range, and altitude.

2.3.5  When fusing or overlaying multiple weather sources, the resulting combined image should convey its intended meaning and meet its intended function, regardless of any differences in the sources in terms of image quality, projection, data update rates, data latency, or sensor alignment algorithms, for example.

2.3.6  If weather information is displayed on an HUD, the guidance of this AMC including its Appendix 6 should be followed.

2.3.7  When the source of the weather information source is not the on-board sensors, some means to identify its relevance (e.g. a time stamp or the age of the product) should be provided. Presenting the product age is particularly important when combining information from multiple weather products. In addition, the effective time of forecast weather should also be provided.

2.3.8  If a weather-looping (animation) display feature is provided, the system should provide the means to readily identify the total elapsed time of the image compilation so that the flight crew does not misinterpret the movement of the weather cells. 

2.3.9  For products that have the ability to present weather for varying altitudes (e.g. potential or reported icing, radar, and lightning strikes), information should be presented that allows the flight crew to distinguish or identify which altitude range applies to each feature.

2.3.10 Weather information may include a number of graphical and text information  features or sets of information (e.g. text and graphical Aviation Routine Weather Reports (METARs) and winds aloft). The display should provide a means to identify the meaning of each feature to ensure that the information is correctly used.

2.3.11 If the flight crew or system has the ability to turn a weather information source on or off, the flight crew should be able to easily determine if the source is on or off.

2.3.12 When weather information is presented on a vertical situation display, the lateral width of the weather swath (like that of the terrain swath) should be carefully considered to ensure that weather information that is relevant to the current phase of flight or flight path is displayed. An unsuitable lateral swath width could either mislead the flight crew to abort an operation for weather that poses no hazard, or fail to abort an operation when the weather does pose a hazard. If swath dimensions are automatically controlled, then careful consideration should be given to include only the area that would be relevant to the operation. Means may be provided for the flight crew to select the swath widths that they consider suitable for the phase of flight and prevailing weather conditions. The lateral width of the weather swath (like that of the terrain swath) should be made readily apparent to the flight crew (e.g. use the same swath as is used for the terrain, or display its boundaries on the plan view weather display). Generally, if the vertical situation displays terrain and weather at the same time, the choice of flight-path-centred or track/heading-centred swath should be consistent. If the weather overlay is designed to show a smaller vertical swath than is represented by the altitude scale, then the boundaries of this swath should be clearly depicted on the display.

2.3.12.1 Weather information displayed on a vertical situation display should be accurately depicted with respect to the scale factors of the display (i.e. vertical and horizontal).

2.3.12.2 Consideration should be given to making the width of the information on the weather display consistent with the width used by other systems, including the Terrain Awareness and Warning System (TAWS), if displayed. This should not be interpreted as a restriction precluding other means of presentation that can be demonstrated to be superior.

3.0     On-board weather radar information

3.1     Background

On-board weather radar provides forward-looking weather detection, including in some cases windshear and turbulence detection.

3.2     Minimum performance standards 

The display of on-board weather radar information should be in accordance with the applicable portions of RTCA/DO-220, Minimum Operational Performance Standards for Airborne Weather Radar with Forward-Looking Windshear Capability. TSO-C63d allows exceptions to the minimum performance standards of RTCA/DO-220 for Class A and B radar equipment.

3.3     Hazard detection 

The weather display echoes from precipitation and ground returns should be clear, automatic, timely, concise, and distinct so that the flight crew can easily interpret, analyse, and avoid hazards. The radar range, elevation, and azimuth indications should provide sufficient information for flight crews to safely avoid the hazard.

4.0     Predictive windshear information

4.1     General 

If provided, windshear information should be clear, automatic, timely, concise, and distinct so that the flight crew can easily interpret, detect, and minimise the threat of windshear activity.

4.2     Presentation methods 

When a windshear threat is detected, the corresponding display may be automatically presented or selected by the flight crew at an appropriate range to identify the windshear activity and minimise the windshear threat to the aeroplane.

4.3     Pilot workload

Pilot workload necessary for the presentation of windshear information should be minimised. When the flight deck is configured for normal operating procedures, it should not take more than one action to display the windshear information.

4.4     Windshear threat symbol

The size and location of the windshear threat symbol should allow the flight crew to recognise the dimension of the windshear and its position. The symbol should be presented in accordance with RTCA/DO-220.

4.5     Relative position to the aeroplane

The relative position and azimuth of the windshear threat with respect to the nose of the aeroplane should be displayed in an unambiguous manner.

4.6     Range

The range selected by the flight crew for the windshear display should allow the flight crew to distinguish the windshear event from other information. Amber radial lines may be used to extend from the left and right radial boundaries of the icon extending to the upper edge of the display.

5.0     Safety aspects

5.1     Functional Hazard Assessment (FHA)

Both the loss of weather information and the display of misleading weather information should be addressed in the FHA. In particular, the FHA should address failures of the display system that could result in the loss of the display and failures that could result in the presentation of misleading weather information.

5.2     Misleading information

The FHA should address the effects of displaying misleading information. In accordance with Chapter 4 of this AMC, the display of misleading weather radar includes information that would lead the flight crew to make a bad decision or introduce a potential hazard. Examples include but are not limited to storm cells displayed in the incorrect position, at the wrong intensity, or misregistered in the case of a combined (e.g. fused) image.

[Amdt 25/17]