Factors That Helped Flight 1549 Avoid Disaster

The successful ditching of US Airways flight 1549 in the Hudson River has made headlines all over the world since the mishap occurred on Thursday, and rightly so. At a time when the whole world, and especially the U.S., is in a deep funk, a feel-good story of quick-acting professionalism and heroism by every-day citizens can’t help but lift people’s spirits in the dead of winter. There is already a lot of info on the web and in the main stream media about the crash, so I won’t rehash much of that. I will give my opinion, as an aerospace engineer and private pilot, on the factors I feel helped make the ditching of US Airways Flight 1549 so successful.

When I first heard about the mishap as I left work on Thursday, a co-worker said a flight departing LaGuardia airport in New York city had ditched, and that survivors were seen leaving the plane. My first thought was that the plane, an Airbus A320, had run off the end of a runway and into Flushing Bay by LaGuardia, similar to a USAIR 737 accident in 1989. In that mishap, all but two of the passengers and crew survived, mostly because the plane was in shallow water just off the end of the runway. As more details of flight 1549 emerged, I heard that it had ditched in the Hudson River. Hmmm, the Hudson is on the other side of Manhattan Island from LaGuardia airport, I thought, so this must have been a real, but very rare, ditching of a commercial aircraft on water. As soon as  I got to a TV, I saw that in fact the A320 had glided to a controlled ditching in the Hudson River after both engines “flamed out”, most likely (at the time of this blog entry) to bird strikes. Early pictures showed the plane floating intact, with the nose, wings and the forward two-thirds of the fuselage out of, or on top of, the water, with a bunch of passengers standing on the wings waiting to be rescued. It turned out all 155 passengers and crew survived with minor or no injuries, another rare feat in an even rarer occurrence.
So what went right to make flight 1549 100% survivable? Here is a list of factors I think helped:
1. First, a very experienced flight crew, including pilot Chesley Sullenberger and co-pilot Jeff Skiles. Sullenberger had almost 20000 hours of military and civilian flying, is an adviser on aviation safety issues, and also a glider pilot. Sullenberger’s experience as a glider pilot would have given him knowledge of how an aircraft without power handles inflight, and also provided a rough idea how far the A320 could glide without engine power. Obviously not far enough to get to the closest airport in Teterboro, N.J., so he made the wise decision to ditch on the Hudson river.
2. The A320 had reached a sufficient altitude (about 3000 feet above ground) to allow the flight crew some time to make critical decisions about where they could land. If the bird strike had happened right after lift-off from LaGuardia, their options would have been very limited. This altitude also allowed them to have control of the aircraft all the way down to the water. It looks like they had full control of the A320, and the altitude allowed them to set up a landing on the river just as if it had been a runway. It’s always better to have a controlled crash than an uncontrolled one.
3. The mishap occurred during the day. This is very important. If it had happened at night, it would have been much tougher for Sullenberger to judge how far he was above the water during the ditching. It can be tough even during daylight to judge your height above water due to depth perception issues, but at night, with no visual cues, the aircraft could have hit the water at a higher velocity or sink rate, possible damaging the aircraft further. Also, night time makes it more difficult for rescuers to find victims, and it would be easy for a passenger to slip under the water and drown without rescuers noticing.
4. The A320 did not break up on impact. If the fuselage had broken apart, or a wing broken off, the plane would probably have sunk much quicker, leading to a higher probability of fatalities. It appears that at least one of the engines, which are mounted under the wings, tore off, but without significantly damaging the wings. This is critical too, since the engines probably acted like big scoops when they hit the water.
5. The planes wings were full of fuel, which helped keep the plane afloat. Since the plane had just taken off for its flight to Charlotte, the wing fuel tanks were probably full. Since aviation fuel is lighter than water, the fuel tanks acted like big flotation bags. You can see this in the numerous pictures that show many passengers standing on the wings waiting to be rescued, yet the plane is floating perfectly stable in the Hudson River.
6. The plane ditched on one of the busiest waterways, right next to the largest city, in the U.S., allowing quick response by rescuers. That section of the Hudson has many passenger ferries plying the river from New Jersey to Manhattan throughout the day, and the first ferry reached the downed plane within minutes. On a cold, January day when the water temperature was near freezing, survivors would not have lasted long in the frigid Hudson river. Also, NYC has numerous Coast Guard and police rescue units that were quickly on the scene with boats, helicopters and rescue swimmers to aid in the recovery.
7. Finally, aircraft safety features required by the FAA and developed through years of  aviation accident lessons-learned helped everyone survive. These features include 16-G seats that don’t break away from the floor during a hard impact. When seats break from the floor, it makes evacuating a full plane much more difficult. The emergency slides inflated from the exits are also designed to be used as life rafts, and you can see the passengers sitting on the slides/rafts waiting to be rescued, just as designed. Also, you can see many passengers wearing those yellow life vests that flight attendants demonstrate (but many passengers ignore) before most commercial flights.
Because of the successful outcome of this rare ditching mishap, I’m sure this accident will be studied for years to come by aviation safety experts. When studying aviation accidents, it has been shown that it usually takes a certain chain of events to occur in a particular order for a normal flight to turn tragic. Break any one of those links in the chain, and the accident would not have happened. The same can be said about the survival factors for flight 1549. If any of the factors that I mentioned above had not been present, there is a good chance that some of the passengers or crew on the A320 would not have survived. This time all the factors lined up to their benefit, and for once we can all applaud some very good news.