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Autoland: How pilots land when they cannot see the runway



(CNN) – It's been a smooth plane, and you've used it in a juicy novel on your tablet. You have hardly noticed the captain's half an hour's announcement that "we must start our descent into Vancouver in a few minutes" and that "there are low clouds around the airport."

Next thing you know is flying the plane on the track and starting to brake. Looking out the window, if all you can see is the glow of the white, pioneering lights that glide past, shrouded in thick clouds.

How did the pilots probably get in this pea soup?

They had high tech help.

Hands-free flight

On the basis of the pilot's inputs, an autopilot calculates a path through the air, and it moves an aircraft's control surfaces to fly straight and level, through turns, climbs and descents, or to follow a specific flight plan.

The control surfaces are moving, aerodynamic units on the aircraft's wings and tail, which allow the pilot to control the flight mode (aircraft orientation relative to the horizon).

The first aircraft autopilots were developed more than a century ago by American Lawrence Sperry, whom he demonstrated in France in 1

914.

In 1937, US Army Air Corps experiments in automatic landing systems resulted in the first successful autopilot controlled landing.

But the technology did not mature until the 1960s when British Airways (BEA) – an ancestor of British Airways – began to fly automatic landings using the Hawker Siddeley HS-121 Trident range) passenger jet.

Driven by the often bad weather conditions across the UK and Europe, Trident allowed the ability to do what was described as a "blind landing" that BEA could maintain its flight plans.

50 years later, almost all modern airlines from the smallest regional plane to the largest wide body beam have autoland capacity.

Follow the beams

  High intensity lights at Los Angeles International Airport.

High-intensity approach lights up at Los Angeles International Airport.

David McNew / Getty Images

When clouds surround an airport, pilots have been able to find their way to the track for decades using an instrument landing system or ILS.

Earth-based transmit projects a radio beam just down the middle of the runway, and another angled up from the path threshold into a gentle three degrees.

During a procedure, a screen on the aircraft's panel shows pilots whether the aircraft is on the left or right of the track – on the locating beam – and above or below the descent path, called the glide path.

To complete a safe landing, pilots should be able to see the runway at a certain decision height (DH) above the ground. At least horizontal visibility is also specified, called Runway Visual Range or RVR. RVR is measured on the ground and the information to the pilots before they begin an approach.

By DH, whose pilots cannot see the runway environment – which may include the runway's high intensity access light – – the crew must climb away from the airport and either try again or go to an airport with better weather.

Generally, the minimum height of an approach is at least 200 meters above the ground depending on the location of the airport and the surrounding terrain. With extra equipment on board and a closely calibrated ILS system, the minimum can drop to 100 feet.

Zero-zero

ILS approaches are by category. CAT I has the highest minimum, CAT II is lower, and three levels of CAT III approaches lower the decision height to zero height and zero visibility – a true autoland and rollout.

The first aircraft certified to fly a zero-zero approach was Lockheed L-1011 TriStar, in the 1970s. The early broad body was equipped with a Collins Aerospace autopilot, and the company continues to make sophisticated advanced systems for many airlines, including the Boeing 737MAX and forthcoming 777X and Airbus A220.

But it's not just about computers, explains Craig Peterson, senior director of commercial systems for marketing Collins Aerospace.

"The inclusion of the flight crew is the key to the entire auto-land operation. Not only must the airport installation and the aircraft be approved for autoland operations, the flight crew must also be trained and approved to perform them. The Autoland system is a complex system of high integrity due to The Critical Critical Character and Flight Crew must continuously monitor the system's operation and performance. "On a CAT III Auto Country approach, pilots cross the aircraft's speed and path to the track and are ready to take over from the computer if a system error occurs.

In order to become highly skilled and certified to fly autoland operations, pilots exercise intensive and sweaty training sessions in terrestrial simulators – those with ultra-realistic graphical displays, controls, and cockpit movements that precisely duplicate the flight experience.

Sim sessions

"The simulator is so accurate and we can reproduce the worst weather conditions," explains John Mulder, chief pilot, aeronautical operations to the Calgary-based WestJet. "It's the best place to train for CAT III approaches. In the simulator we tend to go straight to the limits and capacity of the aircraft."

The Canadian airline has a large fleet of Boeing 737s, including the latest 737MAX, and will soon fly the worldwide Boeing 787 Dreamliner.

WestJet's 737s are equipped to fly CAT III approaches down to a decision height of just 50 feet, the height at which the captain must quickly determine whether to allow the aircraft to land or interrupt.

"There is a radar on the bottom of the plane that measures our distance to the ground, past high-intensity orbit, and at that time we will be above or beyond the orbit of the threshold," Mulder said. "We need to have the landing environment in sight or we want to go around."

Many airlines can fly complete CAT III zero-zero approaches with additional built-in computers and systems that automatically track the track's midline after touchdown, apply the brakes and bring the aircraft to a safe taxi speed.

  A WestJet 737 looks out of the clouds on the short last approach to Vancouver.

A WestJet 737 looks out of the clouds on short last approach to Vancouver.

Howard Slutsken

Firm but fair

Pilots know that passengers will give high marks to a smooth landing when it feels that the wheels have simply rolled on the track.

But in rainy or snowy weather, it is not necessarily the best way to put the plane down, according to Mulder. "We actually have a landing that is a little firmer to break the wheels through any kind of pollutants to get them fixed on the ground, so the brake can be effective."

This kind of touchdown is programmed in autoland systems, although passengers may want to land on an aircraft carrier instead of a runway.

So who do the more consistent landings, pilot or computer?

"Well to be honest Fixed landing is the better landing," Mulder said.

"I suppose I should give it to the autoland system."


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