By Suad Cobo
Ever wondered how an aircraft lands in a fog with absolutely no visibility? There is a lot of technology involved, all to get you on time to the airport in the best interest of safety for all.
Attitude Indicator on the Primary Flight Display of an Airbus A320 (Credit: Baltic Aviation Academy)
WARNING: This article is not intended for real-world use!
The Autoland Systems
Autoland systems were designed to make landing possible in meteorological conditions too poor to permit any form of visual landing, although they can be used at any level of visibility. The autoland system incorporates numerous aircraft components and systems such as the autopilot(s), autothrust (controlling the thrust on engines automatically, depending on the phase of flight), radio altimeters, which measure aircraft’s altitude above ground level, and nose wheel steering. Depending on aircraft type and installed autopilot system, autoland may be used in any weather conditions at or above published weather miniums on any runway with an Instrument Landing System (ILS) installed.
Instrument Landing System (ILS)
The ILS is used to help provide lateral and vertical guidance to the pilots when landing an aircraft. Whilst the ILS is used for most landings, it is most useful when it is cloudy or visibility is poor, as it allows the pilots (or autopilot) to fly the aircraft all the way down to the runway even if they only manage to see the runway in the final few seconds.
The ILS works by sending 2 beams up from the landing runway, one telling the pilots if they are high or low (the ‘glideslope’) and the other telling them if they are left or right of the runway centreline (the ‘localizer’). The ILS receiver on the aircraft measures the difference in depth of modulation (strength received) of radio waves between the signals. For most ILS’s the pilots should be lined up with the localizer and on a 3-degree glide path, but some ILS’s, like at London City Airport, have a steeper approach of 5.5 degrees.
There are three main categories (CATs) of ILS precision approaches: CAT I, with a minimum visibility of 800 m and a decision height (the minimum height at which a pilot can abort the landing and go-around) not lower than 60 m (200 feet); CAT II, with a decision height between 60 and 30 m (100 feet); and CAT III, depending on the current visibility, does not have any decision height, meaning the pilot can abort the landing at any time, sometimes even when the aircraft touches the ground. The last category is used when performing the autoland; however, it can be used regardless of outside visibility. Not all airports and runways, as well as aircraft, are certified for this type of approach. That’s why it is mostly seen in bigger commercial airports.
Performing the Autoland Procedure
Pilots will first check the appropriate information services, such as the Automated Terminal Information Service (ATIS), Meteorological Aerodrome Report (METAR), Aeronautical Information Publication (AIP) of the country they are flying in, and others. First, they start by entering the ILS radio frequency of the runway they want to land on, in the Flight Management Computer or on the radio equipment on board. Then, the Flight Director (FD) will be shown on the attitude indicator (shown in the red box in the picture). Pilots will, with the help of the autopilot, try to align it so that they come to the center of the attitude indicator. The only thing left is to monitor the systems onboard, the altitude and speed, nearby traffic and terrain, or any significant weather shown by predictive systems. The Ground Proximity Warning System (GPWS) will give aural warnings to the pilots on which altitude they are, starting with 2500 feet on most aircraft. The aircraft, if it and the airport’s ILS system are certified for CAT III approach, will land and flare itself. Autopilot disconnects automatically after roll-out on the runway.
You can see this system in action on an Airbus A320 family simulator, shown by a professional pilot, on this YouTube video by the Baltic Aviation Academy.
References
Autoland. (n.d.). Retrieved from Skybrary (English): https://www.skybrary.aero/index.php/Autoland
What’s an ILS?. (n.d.). Retrieved from Flight Deck Friend (English):https://www.flightdeckfriend.com/ask-a-captain/whats-an-ils/
Precision Approach. (n.d.) Retrieved from Skybrary (English): https://www.skybrary.aero/index.php/Precision_Approach
Airbus A320: Auto Landing Tutorial. (n.d.). Retrieved from Baltic Aviation Academy Training (English): https://youtu.be/LIaMALJjOEc