Below is some amazing footage of the US Airways 1549 crash and subsequent rescue effort.

As a private pilot and aerospace engineer, I have been captivated by this story. I know that when things go wrong in the air, everything usually goes much worse when the airplane reaches the ground. Aircraft need to be light. Their structures are only strong enough to resist the forces encountered during normal takeoffs, flights, and landings, plus a relatively small safety factor. Unlike automobiles, aircraft just aren’t designed to crash. Instead you could say that aircraft are designed to not crash. Every critical system on a commercial aircraft is present in duplicate, triplicate, or more. Extensive design and testing goes into making sure that if one or two things fail, the airplane keeps flying right along.

In the case of US Airways Flight 1549, the redundant system was the aircraft’s engines. If one engine goes out, the second engine has enough power to bring the aircraft safely back to the airport. Due to the high reliability (and costs) associated with modern turbofan engines, aircraft manufactures and the FAA have decided that two is enough. Even the 368 passenger, transcontinental Boeing 777 gets by with just two engines. The probability of them both failing simultaneously is extremely low. Turbofan engines can suck up all kinds of junk and keep running. In fact, manufactures do a lot of testing to make sure this is the case:

However, engines have their limits, and those limits were exceeded on Flight 1549, probably by a flock of Canadian Geese. The geese can weigh 14 pounds or more, which is too much for an engine to withstand. The impact probably broke several fan blades. With the fan spinning at several thousand revolutions per minute, the vibration likely cause a complete failure of the engine. The extremely unlucky thing is that it happened twice to Flight 1549.

Large, heavy commercial aircraft don’t fly very well without their engines. While a sailplane can have a glide ratio of around 60, meaning for every foot of altitude it loses it can travel forward 60 feet, an Airbus full of passengers and fuel has a glide ratio of maybe 12. If the aircraft lost power at 3000 feet, it could glide up to 6.8 statue miles under ideal conditions. This wasn’t enough distance to return to LaGuardia. There was an airport in New Jersey that was close, but probably not close enough, and near heavily populated areas. Keep in mind that the aircraft was probably traveling at 130 to 180 miles per hour, which gave the pilot only 2 to 3 minutes to make a landing. He had to make a quick decision under amazing pressure, and he the right thing by choosing the river.

Not to say a water landing is without risk. A lot of force is involved in hitting water at such high speeds. It is amazing that the aircraft didn’t cartwheel or break apart. While the aircraft appears to be intact in the video, this new photo of the plane being pulled from the river shows extensive damage to the underside:

Michael Appleton, New York Times

Just as oil floats on water, an airplane full of jet fuel is fairly buoyant, which is lucky for the passengers given the frigid temperature of the water. The fast response of the ferry boats is also extremely lucky and amazing. The boat captains did an excellent job of reaching the aircraft and maneuvering their vessels as the plane drifted downriver. The compassion of the ferry passengers is also heartwarming.

Overall it’s just so nice to hear a big news story with a happy ending, as that doesn’t happen very often these days.

If you want to read another story of inflight engine failures and amazing heroism, but with a less happy ending, look up United Flight 232. I was very priveledged to hear Captain Haynes speak at my school many years ago, and his story is another example of how well some people can perform under extreme pressure.

If you frequent Digg, you may have already seen this, but it’s worth sharing in case you missed it.