Why can't you ditch your aircraft in the sea?

Question

Disclosure: I'm just a random guy who knows nothing about aviation. :-)

---

I read:

A voice in my earphones was shouting: “Ditch the plane! Ditch it in the ocean!”
It must have come from the tanker skipper or one of the destroyer commanders down below, because every jet pilot knows you can’t ditch a jet and survive. The plane would hit the water at a very high a speed, flip over and sink like a stone and they usually explode on impact.

Okay, but the physics-y side of me wonders why you can't do the following:

• Get ready to jump out (open windows, remove all attachments, etc.)

• Glide down as close to the surface of the ocean as possible, maintaining some momentum

• When you're as low as possible (but still high enough to allow this maneuver), suddenly pull up the nose as high as you can while keeping altitude constant as long as possible

I expect that, if done properly, this could nearly halt horizontal motion of the aircraft; when the momentum is finally lost, I expect the plane would suddenly "drop" in the water from a few feet above, after which you can (hopefully?) jump out of the cockpit immediately.

Now I'm not expecting a 100% survival rate here (I'd almost certainly die trying this), but it certainly seems to potentially beat jumping out of your plane at 15,000 feet and risk getting chopped up by the tail or having your parachute not open (and consequently breaking your spine, etc.).

Where am I going wrong with this? Why is ditching your aircraft in the ocean not an option?
(Does it e.g. depend on the type of the plane?)

Answer 1

The writer was dramatizing things a bit maybe, it's possible to ditch a jet fighter and survive, however your chances are much better ejecting.

Ditching is an option for any aircraft, with some airplanes ditching is the only option if there's a loss of power over water, for example commercial jets have no mode of egress other than the doors. I fly light single engine aircraft and the majority of the time I have no parachute, if my engine throws a rod over a big body of water that's where I'm going to go, and even if I had a chute I'd probably elect to ditch anyway. It's survivable, and many cases people do. The "Miracle on the Hudson" is a famous example, they even made a movie about it, but there are many others where a reasonable percentage of people on board survived.

You are proposing a low speed ditching in a fighter airplane, which has a number of drawbacks:

1. Ditching speed: You can't stop an aircraft by raising the nose higher because at some point you will stall the wings, and they will lose lift. A wing requires smooth airflow to create lift, if the airflow separates from the top surface of the wing it will stop flying, a condition known as a wing stall. In a jet that speed will likely be in excess of 130 knots (150 mph), and there's nothing you can do to slow it further than that. At that speed water cannot get out of the way fast enough and is very, very hard, not some sort of pillow which will cushion an impact
2. Slow speed controllability: Fighter jets are designed for high speed maneuverability, not low speed flight, fly too slow and you can lose directional stability and control
3. Loss of hydraulics: most fighters have assisted controls which require engine power for the pilot to operate easily, lose power and they lose effectiveness even with auxiliary power being generated
4. Unknown sea conditions: Sea conditions can have an enormous impact on ditching survivability, the successful ditchings I can think of were in relatively calm conditions where the pilot was able to make a good, even contact with the water. Dig a wing in and the drag will swing the airplane around, most likely breaking it up. It's very hard to gauge sea conditions from any sort of altitude; what looks calm from 5,000ft up could very well be heavy swells once you're close

So what you are suggesting is that a pilot skims the surface of possibly high seas, bleeding off speed in an airplane with progressively degraded control authority - which is also on fire. It's possible, but highly unlikely to work.

The most critical reason the pilot in the tale you linked to had to escape the aircraft was that a fire in the engine would melt the linkages for the rudder and elevator controls in the tail, or cause a catastrophic structural failure long before he could have ditched, causing a total loss of control. There's no chance that would have been survivable.

Answer 2

First, I'm taking this to be about fighter jet aircraft and similar. Airliners, general aviation jet aircraft, and others, are different, and there have been plenty of examples of jet aircraft ditching in water and everyone surviving. US Airways flight 1549 is a relatively recent (January 2009) example where an Airbus A320 jet aircraft landed on water. It's not something you want to do, and it's not something that happens regularly, but given the right conditions it absolutely can be survivable.

Modern fighters are unstable. They won't maintain stable, even descending, flight on their own; rather, they require constant, tiny adjustments to their control surfaces just to maintain level flight, let alone maneuver. This is done because it allows much tighter maneuvering, which is a much-sought quality in many small military aircraft. As long as everything is working correctly the computers handle much of the minutiae of this, so that the pilot can focus on their mission.

If the pilot is going to eject, you want to do that at some altitude, if for no other reason then because the parachute needs time to deploy. You don't want to eject near the ground if you can avoid it, and not all planes that have ejection capability are rated for zero-altitude ejections. Few are rated for "zero/zero" (zero altitude, zero forward speed) ejections, which are basically "sit on the tarmac and pull the lever".

Every aircraft (actually, airfoil) has what is known as its stall speed. This, simplified, is the lowest speed at which controlled forward flight is possible. The exact value for the stall speed varies both with the aircraft and with conditions (temperature, load, control surface settings, ...) but any fixed-wing aircraft needs considerable forward speed for the wings to generate sufficient lift to not stall. Landing an airplane is, very broadly speaking, executing a well-controlled stall. Once the aircraft gets below its stall speed, it becomes basically a large brick, and drops towards the ground. (Things like vectorable thrust and VTOL designs make this somewhat more complicated in reality, but the basic principles are similar.)

It is correct that by pitching up, you are going to lose forward speed (due to drag). The axiom when landing a fixed-wing aircraft goes like power for altitude, pitch for speed, meaning that you adjust your altitude primarily by adjusting power, and your speed primarily by adjusting pitch (nose up or down). (Compare this to movies, where the direction an aircraft is moving in is often controlled almost exclusively by the control column or stick, and seemingly almost never with power.)

Now, let's apply all of this to your third bullet point:

• When you're as low as possible (but still high enough to allow this maneuver), suddenly pull up the nose as high as you can while keeping altitude constant as long as possible

I expect that, if done properly, this could nearly halt horizontal motion of the aircraft; when the momentum is finally lost, I expect the plane would suddenly "drop" in the water from a few feet above [...]

Yes, it's probably going to slow down the aircraft's forward speed.

Unfortunately, the aircraft will drop when it slows down below its stall speed, at which time it still has a significant forward speed.

This means that when the aircraft hits the water, it is still moving forward quite fast. Fast enough that the water doesn't have time to move out of the way.

What you are doing then is akin to performing the same maneuver over a similarly rough concrete surface. Remember that by the time you are even considering ditching in the first place, the aircraft is probably damaged or crippled in some pretty fundamental way; otherwise, why not just land normally? Even a very hard landing that ends up breaking the landing gear is far better than a ditching. Unless the water is near perfectly smooth (similar to a runway), when the aircraft hits the water, it is going to come to an abrupt halt, which causes significant forces both on the airframe and its occupants. It's like they say, it's not the fall that kills you, it's the sudden acceleration at the end of the fall. (Conditions may apply.)

[...] it certainly seems to potentially beat jumping out of your plane at 15,000 feet and risk getting chopped up by the tail or having your parachute not open [...]

"Risk getting chopped up by the tail" is why any sane ejection system starts by giving you a significant vertical boost. "Having your parachute not open" is a risk, but that's why parachutes are inspected regularly (they are not set-and-forget items by a long shot!) and it probably still beats crashing in an uncontrollable aircraft.

Answer 3

As a hang-glider pilot, I can say that's exactly how a good hang-glider landing goes. We don't land with speed and run it off (at least if we've done it properly anyway). Instead we fly our approach to landing height, burn off speed as necessary to near-stall, then rapidly rotate the wing. The wing effectively turns into an instant air-brake, and we land on our feet, stationary.

It's essential to point out that the wing is above stall speed all the way until that final flare. Inertia is a thing, so if you flare with too much speed on then the glider pitches into the air until it hits stall speed, at which point it comes back down again from a lot higher than you want to be. This generally results in bent aluminium, and often minor injuries to your "undercarriage" as well.

How is this different from a plane? Firstly, a pilot cannot do with their wings what we can do with a hang-glider. The pilot can certainly pull the nose up until the plane stalls, but at low speed they simply can't apply that much pitch-up that quickly. A hang-glider doesn't flare because of airflow over a control surface, it flares because of a massive weight-shift adjustment.

Secondly, even if they could, the plane wouldn't take it. A hang-glider has a stall speed of maybe 20mph. A jet will be well north of 100mph. Trying to apply the same kind of flare at 100mph would simply rip the wings off the aircraft.

Thirdly, consider how long the flare takes. As soon as you're below stall speed, your wing stops flying and you lose control authority. On a hang-glider landing at maybe 20mph, the flare takes maybe 3-4s - but we're still stable in the same way as a parachute is stable, because our centre of mass is below the (falling) wing, and we have some limited ability to control the wing with our bodyweight. On an aircraft landing at something over 100mph, it would take much longer for a flare to burn off all forwards speed without pitching the aircraft into the air, and during this time the plane has no control input whatsoever. Even a positively-stable aircraft such as a high-wing trainer could be knocked sideways by a gust catching a wing; a negatively-stable aircraft such as a fighter jet will simply drop a wing immediately; your control surfaces are no longer working so there's nothing at all you can do about it; and that's an awfully long time to be close to the ground with no say about what the aircraft is doing.

Some jet display teams do a high-AOA pass as part of the display. Don't be fooled. You're a long way away, and that sucker is still moving fast. It just looks slow compared to the speed it was doing earlier!

Note that with a vectored-thrust aircraft like a Harrier, it is possible to completely halt forward speed, because it has the capability to independently apply thrust in a completely different direction. Most planes can't do that though.

As an aside, it's also interesting to look at birds from this POV. Most birds can flare and stop relatively easily, but not all of them. Watch a swan landing. They don't splash down like that for fun, they do it because they have a high stall speed and too much forward momentum.

Answer 4

If you've never seen it, there was a particularly scary video taken of Ethiopian Air 961 crashing in the ocean. The plane had been hijacked and the pilot and copilot were having to fight the drunken hijackers off. Still, it's a harrowing illustration of what can go wrong with landing in the ocean

Leul attempted to land parallel with the waves instead of against the waves in an effort to smooth the landing. Seconds prior to contacting the water the aircraft was banked left some ten degrees; the left engine and wingtip struck the water first. The engine acted as a scoop and struck a coral reef, slowing that side of the aircraft quickly and causing the Boeing 767 to suddenly tilt left. The rest of the aircraft then entered the water unevenly, causing it to break apart. Except for the rear part of the airframe, the broken portions of the fuselage sank rapidly. Many passengers died because they inflated their life jackets in the cabin, causing them to be trapped inside by the rising water.