Electronic Flight Information Systems — Page 289, Lesson 342

I want to walk you through the Electronic Flight Information System, or EFIS, and we're starting with the colour logic and the control panel. This is the heart of how the displays talk to you, so let's build it properly. First, the colour conventions. On an EFIS display, colours aren't just decoration — they carry meaning. Cyan is used for sky shading on an EADI, and for low-priority information such as non-active flight plan map data. So if you see cyan on the map, that's data that isn't currently being flown. Yellow is for ground shading on an EADI, and for caution information — that means failure warning flags, limit and alert annunciators, and fault messages. Red is reserved for the display of the heaviest precipitation levels as detected by the weather radar, which we call the WXR. So red on the weather display means the most intense rain or returns. Now, the Remote Light Sensor. This is a photodiode device. A photodiode responds to light — it converts light into an electrical signal. It sits on the flight deck, senses the ambient light conditions, and automatically adjusts the brightness of the CRT displays to an acceptable level. So when the sun blazes in, the displays get brighter; when it's dark, they dim. You don't touch it — it does the work. Next, the Control Panel. Each EFIS system has its own control panel, and the switches are grouped to control the displays of their respective EADI and EHSI units. The EADI is the Electronic Attitude Director Indicator — the primary attitude display. The EHSI is the Electronic Horizontal Situation Indicator — the navigation display. Let's look at the EADI section of the control panel, because that's where the decision height work happens. There are four controls here. First, the Brightness Control, labelled BRT. You use it to adjust the brightness of the ADI display to the desired level. Second, the Decision Height Selector, labelled DH SEL. This selects the desired decision height for DH alerting. Third, the Decision Height Reset Switch, labelled DH RST. When you press it, it resets a DH alert on the associated ADI, and it changes the RA display from yellow to white. RA is radio altitude. So after an alert, you press this to clear it and the radio altitude readout returns to white. Fourth, the Decision Height Reference Indicator, labelled DH REF. This displays the selected decision height on the controller, and on the EADI itself. So you set it, and you see it in both places. Now, what does the EADI actually show you? It displays normal pitch and roll attitude indications, plus a list of additional data. Attitude data comes from an Inertial Reference System — the IRS. You also get flight director commands, localizer and glide slope deviation, ground speed, radio altitude, decision height, and the Automatic Flight Control System and Autothrottle modes — that's the AFCS and autothrottle. There's also a speed error scale, which is the difference between commanded and actual speed. So if the autothrottle commands 250 knots and you're at 240, that scale shows the error. One important note: the autoland status, and the pitch and roll armed and engage modes, are not selected on the EFIS panel. They're selected on the AFCS control panel. So the EADI displays them, but you set them elsewhere. Finally, let's define decision height precisely, because it's a legal and operational term. Decision height is the wheel height above the runway elevation by which a go-around must be initiated unless adequate visual reference has been established and the aircraft position and approach path have been assessed as satisfactory to continue the approach and landing in safety. Break that down: it's measured as wheel height above the runway elevation — that's the height of the main wheels above the runway. By that height, you must either go around, or you must have adequate visual reference and have assessed that the position and approach path are satisfactory to continue safely. If you don't have that, you go around. That's the decision. So the picture is: colour tells you priority, the light sensor keeps the display readable, the control panel lets you set brightness and decision height, and the EADI presents all that attitude and approach data to you. That's the foundation of the EFIS.