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Why Asiana Airlines Flight 214 Fell Short of the Runway


bobbyburns

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On July 6th, 2013, an incident occurred that could have been avoided.

A massive (up to

297,550 kg) Boeing 777-200ER simply fell out of the sky, not even a mile from the runway's threshold. The 777, carrying 291 people, smacked into the seawall, immediately ripping the tail section off of the fuselage. Directly causing 2 deaths, the crash was the first fatal accident involving this type of aircraft.

Generally, when an aircraft has an outstanding safety record (like the 777), accidents are mainly caused by, sadly, the pilots.

Asiana Flight 214 was no exception.

So, how did the 777 fail to make it to the runway? The answer is annoyingly simple. The pilots (one of whom performing his first landing in a 777 at San Fran) forgot to monitor the most important gauge in their aircraft: the airspeed indicator.

The NTSB reported that the standard approach speed for a 777 is about 137 knots (160 mph, for comparison). Flight 214 came in at a VERY slow 112 knots.

In this case, the pilots were literally on autopilot. They were using "autothrottle", a device that allows pilots to pre-set an airspeed. But using autothrottle doesn't give the pilots an excuse not to monitor their airspeed.

As they flew their approach, they were indicated below their proper glidepath. In other words, they were too low. Their natural reaction was to "pull-up", or pull on the stick, thus raising the nose of the aircraft.

Normally, pitching the nose up will simply make the aircraft gain altitude. But not when you're flying at a dangerously slow 112 knots.

Here's where the physics comes in.

Raising the nose increase Angle of Attack. This angle is defined as the angle between relative wind and the wing itself.

305px-Angle_of_attack.svg.png

If this angle becomes too large, the aircraft will enter what's called a "stall". No, that doesn't mean the engines quit. It means that the wing no longer produces enough lift to overcome the downward force due to gravity, mg.

The end result is obvious. The aircraft stalled. The pilots failed to recover from the stall. In fact, they FURTHER increased the angle of attack, dooming the aircraft.

This is why the safest pilots are the ones who don't rely upon autopilot.

800px-NTSBAsiana214Fuselage2.jpg

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