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A comment by @AsheeshR says:

The Hudson River Landing was due to a combination of piloting skill and an autopilot system that was engaged right till impact and kept the plane in a controlled descent within a safe flight envelope.

It was an Airbus aircraft, so the autopilot has priority over pilot input, but how exactly did the autopilot play a role in getting them down safely?

What exact procedures did Sully and the crew follow when landing? Was there anything in addition to standard ditching procedures, that might have contributed to them landing in one piece?

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The NTSB report is a good place to start. –  fooot Mar 25 at 14:55
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I believe Airbus have a "ditching" switch in the cockpit that seals the hull. –  RedGrittyBrick Mar 25 at 15:09
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@RedGrittyBrick You're right, but it wasn't pressed on this particular flight. –  Danny Beckett Mar 25 at 15:35
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@flyingfisch See youtu.be/Zzjbubs59Ks?t=23m45s - it was at the end of the checklist, which they didn't have time to complete. –  Danny Beckett Mar 25 at 15:36
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@flyingfisch The ditch switch is meant to close openings in the fuselage through which water would make ingress, and slow flooding of the fuselage; however, it wouldn't have done much good in this situation, because the forces of impact ripped holes in the hull anyway. –  tgies Mar 25 at 17:33

3 Answers 3

up vote 19 down vote accepted

The NTSB report is a great resource when looking for information about an incident like this.

There is an Engine Dual Failure Checklist discussed starting in section 1.17.1.2 of the report. This includes steps to attempt restarting the engines, and further steps depending on whether or not the engines can be started, and finally steps to help prepare for a forced landing. Pilots train on engine failures regularly, so they are already familiar with the procedures. The report discusses how their actions compared to what the checklists say. Since the incident occurred at such a low altitude right after takeoff, they didn't have time to complete all of the steps. They did what they had time for, and had to make quick decisions about what their options were.

The report also discusses in section 1.17.3.2 the ditching training the pilots received. There was guidance in the manual, but no specific scenarios included in their simulator training.

The autopilot is great for use in normal situations. However, as soon as anything is going wrong, the pilot should take control of the plane. You do not want to take time to figure out "what's it doing now" in a difficult situation. So in this situation, the autopilot probably disconnected when the engines went out, or was manually disconnected by the pilots.

Section 1.6.3 talks about the flight envelope protections. I believe these protections are what you are referring to when you say that the autopilot has more control. They are designed to protect the plane from stalling or otherwise exiting controlled flight. Because the pilot was able to start the APU to provide electrical power, the plane remained in the "normal law" mode where these protections were available. This limits the control the pilot has in order to protect the plane, in the sense that the plane will override pilot inputs to avoid dangerous situations.

Section 2.7.2 discusses the impact of these protections in this case.

The airplane’s airspeed in the last 150 feet of the descent was low enough to activate the alpha-protection mode of the airplane’s fly-by-wire envelope protection features...

Because of these features, the airplane could not reach the maximum AOA attainable in pitch normal law for the airplane weight and configuration; however, the airplane did provide maximum performance for the weight and configuration at that time...

The flight envelope protections allowed the captain to pull full aft on the sidestick without the risk of stalling the airplane.

An interesting point in the report is that Airbus certified the plane to be able to land on the water intact under certain conditions. Here is how the actual conditions compared to the certified conditions.

Section 1.6.7

enter image description here

The report mentions that it would be extremely difficult to meet all of these requirements in an airplane with no power. The values that are higher, notably the mass and descent rate, are factors in the damage the airplane received.

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How exactly does the Flight envelope protection give the pilot more control?? –  Lnafziger Mar 25 at 15:56
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I think so. The "protections" actually remove some level of control from the pilot (and whether this is a good thing or not is a subject of much debate). Excellent answer though, thanks! –  Lnafziger Mar 25 at 16:02
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Thanks for the discussion. I was skeptical as well, but I added some more detail about how the protections functioned on this flight. –  fooot Mar 25 at 21:20
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As @Lnafziger mentioned, the amount of "nannying" that an Airbus does compared to a Boeing is debated among pilots. Airbus, for example, won't let you jerk the controls to the point of possibly losing control or bending metal. Boeing will let you, so that if you come out of a cloud and see you're going to collide with another plane in 3 seconds, you can pop a few rivets but avoid a mid-air. Boeing also gives a lot more tactile feedback on the controls and involves the pilot more heavily, which can have its advantages (the downside is more routine workload). –  Phil Perry Mar 25 at 22:25
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@GabrielBrito the pilot was pulling all the way back on the sidestick, but the alpha-protection mode limited the amount of elevator deflection to prevent the plane from pitching up too much and stalling. –  fooot Sep 24 at 19:28

There is not much training for situations like that because they are very rare and the simulators cannot teach accurately what to expect when a plane touches down on water.

The captain in this situation got almost everything right for a water landing, as he kept the nose up and wings level, he let the tail hit the water first slowing the plane down enough so it survived the impact.

I'm not sure autopilot played much role in this if any, because there was no runway length and reverse thrust to concider.

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I disagree that there's "not much training for situations like this" - ditching is definitely a commonly practised procedure. –  Danny Beckett Mar 25 at 14:39
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From the Air Crash Investigation episode on this accident @ about 11:25 -- "Investigators Soon Learned that none of the Major Airlines Teach Pilots how to Land On Water. Training for Ditching in water is very difficult, we don't have the models to accurately simulate what a plane will do when it touches down on water, Given the rarity of this type of event it will be difficult to justify training for training pilots for this type of event" –  cytasos Mar 25 at 14:41
    
Thanks for that! It sounds like I stand corrected. Does anyone else know about this? –  Danny Beckett Mar 25 at 15:16
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FWIW, in my 10 years of taking 747 simulator check rides, ditching was regularly practiced. There was a checklist for ditching. It included recommended touchdown configuration, speed, pitch attitude, and admonitions for landing parallel to the swells if possible. There was a lot of work for the flight engineer (3 man cockpit), a lot of setup including making sure the outflow valves were closed and the like. As I remember, the recommended pitch attitude for the 747 was 5 degrees nose up. I can't remember the recommended flap setting. –  Terry Mar 28 at 8:28
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Witch Airline Company generally prepare for water landings more carefully since they melt when they get wet. –  NobodySpecial Mar 29 at 3:18

anything that helped? Luck, pilot skill, luck, just the right weather conditions, luck, nerves of steel, and some more luck.
And they probably managed to get the aircraft so slow at just the right moment that they hit the water at just the right angle and minimum sheer forces to not break up.

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We're looking for long answers that provide some explanation and context. Don't just give a one-line answer; explain why your answer is right, ideally with citations. Answers that don't include explanations may be removed.

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Are you able to expand on your answer at all? For example to include how the A/P played a role, and what inputs the pilots used? –  Danny Beckett Mar 25 at 13:53
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Any reference? Maybe, quotes from the crash report to support your answer? –  AsheeshR Mar 25 at 14:15

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