Autoland: How pilots land when they can not see the runway

(CNN) – It has been a good flight and you've spent immersed in a juicy novel on your tablet. You have hardly noticed that the captain announced about half an hour ago that he "will begin our descent to Vancouver in a few minutes" and that there "are low clouds around from the airport ".

The next thing you know, the camera hits the track and starts to slow down. Looking out the window, just about all you can see is the glow of the white track edge lights that scroll past, wrapped in a thick cloud.

How did the pilots land safely in this pea soup?

They had the help of high technology.

Hands free flight

Based on pilot inputs, an autopilot calculates a trajectory in the air and moves the control surfaces of an aircraft so that it flies straight and level, in turns, uphill and downhill, or that he follows a specific flight plan.

The control surfaces are mobile aerodynamic devices on the wings and tail of the aircraft, which allow the pilot to control the attitude of the flight (the orientation of the aircraft relative to the aircraft). 39; horizon).

The first automatic pilots of planes were developed more than a century ago by the American Lawrence Sperry, which he demonstrated in France in 1914.

In 1937, experiments conducted by the US Army Air Corps on automatic landing systems resulted in the first successfully controlled landing by autopilot.

But this technology did not change until the 1960s, when British European Airways (BEA) – an ancestor of British Airways – began making automatic landings using the Hawker Siddeley HS-121 Trident. short pbadenger jet (and later medium term).

Driven by the bad weather conditions in the UK and Europe, the Trident was able to perform what was called a "blind landing" allowed BEA to meet its flight schedules .

Fifty years later, virtually all modern airliners, from the smallest regional aircraft to the largest jumbo jet, have an autoland capability.

Track the shelves

When clouds surround an airport, pilots can find their way to the runway for decades using an instrument landing system, or ILS.

Ground-based transmitters project one right radio beam in the middle of the runway and another from the runway threshold at an angle of 3 degrees.

When approaching, a screen on the aircraft panel tells pilots if the aircraft is to the left or right of the runway – on the centering beam – and above or below below the glide path, called the glide slope.

To make a safe landing, pilots must be able to see the runway at a specific decision height (DH) above the ground. A minimum horizontal visibility is also specified, called the runway visual range or RVR. The RVR is measured on the ground and the information is given to the pilots before they start an approach.

At the DH, if pilots can not see the runway environment (which may include high intensity approach lights), the crew must move away from the airport and attempt again or surrender at an airport where the weather is milder.

As a rule, the minimum altitude at the approach is at least 200 feet above the ground, depending on the location of the airport and the surrounding terrain. With additional equipment on board and a tightly calibrated ILS system, the minimums can drop to 100 feet.

Zero-zero

ILS approaches are categorized. CAT I has the highest minimums, CAT II is lower, and three levels of CAT III approaches reduce decision height to zero altitude and zero visibility – a true autoland and deployment.

The first aircraft certified to perform a zero-zero approach was the Lockheed L-1011 TriStar, in the 1970s. This first widebody aircraft was equipped with a Collins Aerospace autopilot and the company continues to manufacture sophisticated systems and high technology for many airliners, including the Boeing 737MAX and the future 777X, as well as the Airbus A220.

But it's not just about computers, says Craig Peterson, senior director of marketing systems marketing at Collins Aerospace.

"The involvement of the flight crew is essential in the overall operation in autoland.Not only the installation of the airport and the aircraft must be approved for autoland operation, but they must also be trained and licensed to perform them.The autoland system is a complex system with high integrity due to its critical safety character, and the flight crew must the operation and performance of the system. "

In a Category III autoland approach, pilots check the speed of the aircraft and its path to the runway and are ready to take over the computers in the event of a system failure.

In order to become highly competent and certified for autoland flights, pilots undergo intensive and sweat-prone training on ground-based simulators – ultra-realistic graphical displays, command and control movements. piloting faithfully reproducing the flying experience.

Sim sessions

"The simulator is so accurate and we can reproduce the worst weather," says John Mulder, chief pilot, Flight Operations WestJet, Calgary. "It's the best place to train at CAT III approaches." In the simulator, we tend to go to the limits of the capabilities and capabilities of the aircraft. "

The Canadian airline has a large fleet of Boeing 737s, including the newest, the 737MAX, and will soon be flying the Boeing 787 Dreamliner, which covers the world.

The WestJet 737s are equipped to perform CAT III approaches up to a decision height of only 15 meters (50 feet), at which altitude the captain must quickly decide to let the landing gear land or d & # 39; Interrupt the approach.

"There is a radar at the bottom of the aircraft that measures our distance to the ground.We will have pbaded the high intensity runway lights and at that point we will be above or beyond the threshold of track, "said Mulder. . "We must have the landing environment in sight or we will go around."

Many airliners can complete full Zero Zero CAT III approaches, with additional onboard computers and systems that automatically follow the runway centreline after touchdown, apply brakes, and put the engine in motion. airplane at a safe driving speed.

Farm but just

Pilots know that pbadengers will give high marks for a soft landing when they get the impression that the wheels have simply rolled on the track.

But in rain or snow, this is not necessarily the best way to land the plane, according to Mulder. "We really like to have a firmer landing to break the wheels through all kinds of contaminants, to put them firmly on the ground so braking can be effective."

This type of landing is programmed into autoland systems, although pbadengers may have the impression of landing on an aircraft carrier rather than on a runway.

So, who makes the most consistent landings, the pilot or the computer?

"Well, to be honest, the firm landing is the best landing," said Mulder.

"I guess I should give that to the autoland system."