Why perfecting visual approach landing is necessary for pilots

The Asiana Airline plane that crash landed in the US. Speculation has centred on whether this was a badly managed visual approach. Photo/AFP 

Last week, an Asiana Airlines Boeing 777-200 arrived at San Francisco after a scheduled ten-hour flight from Seoul.

The weather at the time of arrival was good, but the instrument landing system— specifically the part that provides vertical guidance —had been declared unserviceable. Consequently the air traffic controllers cleared the plane for a visual approach to runway 28L.

This routine approach, however, ended in tragedy when the airliner touched down short of the runway.

The plane hit an edge — shearing off the wheels and the tail section, skidded along the ground and finally burst into flames. Amazingly, only three people died.

While it’s still early in the investigation, speculation has centred on whether this was a badly managed visual approach worsened by a misunderstanding on the operation of the auto throttle.

With a visual approach, you look outside the window, determine where you want to go and fly the plane there; It’s how we all initially learn how to fly.

Instrument flying relies on navigation aids. By not referencing visual cues, you are able to land in poor weather, relying on your instruments to guide you to a point where you can see the runway.

Unlike a car, a plane does not simply turn; it banks. This bank changes the heading, which in turn takes you to your preferred point; it’s a little bit like reversing a car, only more complex.

On the vertical front, you have to point the nose at a point just before the runway if you want the plane to go to your visual aiming point.

Any change in the airplane configuration, or outside conditions, changes the amount of force you have to apply on the control column to keep the plane flying where you want it to go.

To round it all off, there is a lot of lag when flying large planes. The jet engines take about eight seconds to spool up from idle to full power, and any control inputs will take some time before being reflected in the aircraft flight path.

All this time, a pilot is also supposed to monitor the speed displayed inside the cockpit. Once a plane slows down beyond a certain speed, it stalls and becomes a large rock.

To make it easier on the pilots, manufacturers have made some improvements on their planes.

Fly by wire controls, such as those on the 777, have made flying significantly easier by eliminating most of these extraneous forces.

Flight directors, horizontal and vertical bars on the displays, free the pilot from having to judge all those parameters.