Ask Captain Lim

Dear Captain Lim,

I read from the newspaper that a Cathay Pacific A340 Airbus continued its journey from Vancouver to Hong Kong with a broken wind screen. I wonder if this is too dangerous for the pilot to continue with the journey.

Why didn't the captain of the Airbus divert his plane to a nearest airport for an emergency landing instead of continuing with the journey? The flight finally landed at Seoul due to insufficient fuel to proceed onto Hong Kong.

Although the news reported that the wind screen is made of 3 layers of glass (I doubted that the wind screen should be made of acrylic resin), will it break into pieces when the internal compartment is pressurized.

Can you explain how a well-trained pilot deal with this kind of emergency?

Janus Poon

Hi Janus,

There is indeed a special procedure for the pilot to handle such a problem. If one ply of the glass failed, the windscreen is still able to sustain the maximum differential pressure. However, since the pilot was unable to accurately determine how many plies have failed, the differential pressure must be reduced and he must descend to a lower flight level.

If the Airbus A340 has to fly at a lower level, it means that it would consume more fuel. Hence it had to divert to Seoul.

Unlike the car windscreen which would normally break into pieces when cracked, the plies in the windscreen are there to strengthen it.

So when a crack is noticed, the captain would refer to his manual that lays down the steps to be taken. It was not dangerous for the captain to continue with the flight as all pilots are trained to handle such kind of emergency whenever it arises.