Electronic docking guidance systems have come a long way since they were introduced in the 1970s.As well as helping aircraft get on stand with the minimum of fuss and delay, they are also playing anincreasingly important role in the management of ramp operations
Initially, visual docking guidance systems took the form of passive ‘azimuth’ devices that simply showed where the pilot was in relation to the correct stop position. The AGNIS (Azimuth Guidance for Nose-In Stand) system, consisting of two coloured lights mounted side by side, was for years one of the most common stand guidance systems. A pilot correctly lined up on the stand centreline sees two green lights but – if not – one of the lights will appear red until the aircraft is steered towards the green one.
Systems like this can only tell the pilot whether or not the aircraft is properly lined up on the centreline, not when they need to stop, so a simple Parallax Aircraft Parking Aid (PAPA) was added, consisting of a light inside a box with a rectangular slot in the front. The perspective effect makes the light appear to move from one side of the slot to the other as the aircraft gets closer, and the slot has markings to show where different types of plane should stop. It is crude but effective, although the system is inaccurate if an aircraft is significantly off the centreline.
There may also be red and green stop lights, usually round rather than square like the AGNIS lights with which they could otherwise be confused, and mounted vertically, rather than side by side. These simple systems must also be set up on the assumption that the pilot is in a specific seat and if anything alters on the ground or the aircraft type changes, the system has to be moved around too.
Gradually, these systems evolved into the sophisticated systems found in almost all airports in the developed world, which can not only get aircraft safely to the gate but are beginning to provide a whole host of other information too. The most effective systems available today can distinguish between different types of aircraft and automatically adjust; they are also effective in poor weather or light conditions – which is, arguably, when they are most needed. Nor are they dependent on whoever is controlling the aircraft being in a specific seat.
Camera-based Advanced Visual Docking Guidance Systems (A-VDGS) were the first radical development and, while a great advance on what was available before, cameras have the disadvantage that they need a certain amount of contrast to work effectively – so they are not so effective in poor light conditions. Fog and rain can drastically reduce the effectiveness of camera-based systems.
The next development was a system based on a two-dimensional laser scanner and, eventually, in the case of Safegate Group, three-dimensional lasers. (Safegate is the dominant company in the A-VDGS field; it claims over 80% of the world market.) Two-dimensional lasers cannot scan horizontally and so have to be physically aligned with the centreline, which limits where an A-VDGS system can be mounted; nor does such a system allow for multiple or curved centrelines, and it cannot differentiate between different types of aircraft. A separate azimuth guidance device also has to be provided as a two-dimensional scanner. Plus, if the aircraft is anywhere but perfectly aligned with the centreline as it approaches, distance-to-go will not be accurate either.
Safegate says that its three-dimensional laser-based A-VDGS systems overcome these limitations, because – being able to scan horizontally as well as vertically – they can differentiate between different aircraft types; moreover, they are less dependent on the aircraft following the centreline perfectly for accurate distance-to-go information.
Safegate has around 7,000 systems installed around the world and sells around 6-700 new ones every year. With such a large market share, it has the advantage of familiarity – pretty much every pilot will be familiar with the company’s systems, which come in T3, T2 and TI versions. T1 is actually the most sophisticated, with features such as apron scans, better aircraft verification and a warning system if the passenger boarding bridge is out of position.
Safegate International marketing director Johnny Åkerman says that his company sells most systems to expanding airports that are opening new gates and terminals, although there is also a good market in places like Africa and the rest of the developing world that are procuring docking guidance systems for the first time. New and bigger aircraft are less of a driver, however, as the modern systems are so flexible that they can cope with most new designs without modification – with the exception of the need to install larger screens for the A380 because the distance-to-go has increased.
The systems also provide that extra reassurance that nothing is in the way of an aircraft as it approaches, thanks to apron-scanning capabilities. Certainly, the ground crew should be checking for obstructions too, but the A-VDGS provides useful insurance for backing up fallible humans. It can also provide information on where the aircraft is on push-back, before it gets picked up by the ground radar system.
But perhaps the most exciting area of A-VDGS is when the aircraft has docked, Åkerman observes. All its systems can be linked up with the airport’s, and can provide data such as expected departure time, how much pre-conditioned air has been taken or how much electricity has been used. It can even be used as a basis for invoicing – one less piece of paper for airline and airport managements to chase after.
The full value of an advanced docking guidance system comes when it is interfaced with airport central databases like AODB (Airport Operational Database) or FIDS (Flight-Information-Display-System), adds Sweden-based system maker FMT. Interfacing FMT’s laser-based APIS++ advanced visual docking guidance system – through the Atlantis stand management system – to either AODB or FIDS allows it to be automatically set for the arriving aircraft type and series.
The APIS++ system now boasts greatly improved aircraft recognition capability, says FMT, adding that the industry is now demanding approaching aircraft to be 100% confirmed by docking systems. Advanced visual docking guidance systems have until now had trouble differentiating between, say, aircraft of different types that share the same fuselage and engines. However, FMT says its new technology can identify the aircraft’s individual registration number, giving 100% confirmation that the stand pre-setting is correct. This is based on information sent from the aircraft’s transponder.
APIS++ can also be interfaced with passenger boarding bridge software, allowing it to be pre-set at the touch of a button and locked until the aircraft is Block On. The bridge can then be automatically adjusted for the type of aircraft.
Azimuth guidance is provided by the patented Moire technique – light passing through superimposed gratings creates a pattern that is independent from the laser. An arrow pattern indicates when the aircraft is not on the centre line, changing to a straight vertical line when it is. Obstacle scanning is now standard.
The closing rate display changes from green to yellow to red and the indicator becomes shorter.
APIS++ can also be equipped with Azimuth co-pilot guidance from the right-hand seat, if desired. But FMT recognises that total automation is not always desirable; the system can be equipped with traffic lights to be used in a manual talk-back procedure – the lights can be manually operated over a handheld control panel.
Dallas/Fort Worth International Airport (DFW) is a typical, and very prolific, user of Safegate’s Safedock systems. The southern US gateway first installed Safedock’s A-VDGS in 2007 when the airport, American Airlines and Safegate worked together on a system that would be able to dock and deplane aircraft during “irregular operations” events and particularly when aircraft ramps were closed due to lightning.
The airport now has over 150 Safegate docking systems, with gate A-VDGS at four of its five terminals, and there are plans to expand usage still further. It is upgrading existing systems, installing them where none exist at present and including A-VDGS in new piers and terminals.
DFW’s assistant vice president for information technology systems, John Parrish, says that, above all, airports look for “a system that can do the job safely and reliably. When this project began, Safegate stood out because it used laser technology to detect and guide the aircraft, rather than video analytics.”
DFW has no particular policy on standardising systems and, for the present at least, there is no US government or official policy on A-VDGS. The International Civil Aviation Organization (ICAO) does define specifications and recommendations for A-VDGS, though without mandating their use, however, and the Safedock system meets all of these.
Safedock has demonstrated its value “because of its ability to significantly minimise delays during irregular operating conditions”, although it also makes regular operations more efficient, Parrish considers. It even saves on airline fuel costs because it allows aircraft to taxi all the way to the gate without stopping. Safegate systems also run the Ramp Information Display Systems (RIDS) throughout DFW.
But it is the ability to capture other data, like power or air consumption through the A-VDGS, that is most critical, Parrish says. DFW’s goal is “consistently repeatable success” he continues. “DFW is committed to the concept of Airport Collaborative Decision Making. Basically, that means that we gather and distribute information about every aspect of the aircraft movement and the people and processes that all have to work in complete harmony to deliver a seamlessly safe travel experience. Although it must appear effortless to our guests, hundreds of thousands of data elements have to be gathered in real-time, evaluated and responded to. A-VDGS is one of many important players on the collaborative team.”
DFW’s Safedock systems are designed to be as near foolproof as human ingenuity can make it, and operational availability is 98.99%, Parrish enthuses. DFW and Safegate have installed redundant systems spread across disparate production servers in a distributed environment that includes virtual applications and databases as well as redundant mirror partners, independent generators and back-up uninterruptible power supplies, in order to guarantee maximum reliability. But, if all else fails, airline ground personnel are on the ramp to marshal aircraft in the time-honoured traditional manner if need be