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Emergency Landing of an Aircraft on Water.
A Hazardous Manoeuvre
Ditching an aircraft into the sea, a river, or a lake, is an extremely hazardous manoeuvre which is only contemplated when no other option remains realistic in an emergency situation. This may be because the aircraft cannot reach a runway, or open ground free of obstacles.
There is a strong likelihood that the aircraft will break up on impact with the water. These structural breaks are most likely at the wing root and/or in the centre/rear fuselage. If the crew and passengers survive the ditching then, even with protective clothing and equipment, they may die of hypothermia before they are rescued.
Some of the possible scenarios which might lead to a decision to ditch the aircraft are:
- Fire: An uncontrollable fire, either within the fuselage or on the wing where the continued control of the aircraft or the survival of the occupants for the time required to reach a runway is doubtful; for example see the article: NIM, vicinity RAF Lossiemouth UK, 1995 (FIRE)
- Fuel Exhaustion: A fuel leak that results in insufficient fuel to reach a runway;
- Multiple Engine Failure: Failure of multiple engines, for example:
- fuel contamination,
- volcanic ash encounter,
- multiple bird strike. for example see: A320, vicinity LaGuardia New York USA, 2009 (BS LOC AW)
Consideration and Techniques for Ditching an Aircraft
The following is a list of generally accepted considerations and techniques for ditching that could be applied to virtually any aircraft type. Keep in mind that "ditchablility" is not part of the design criteria for the vast majority of aircraft types.
- Power On. If there is a choice in the matter, power on is preferable to power off for ditching. Use of power allows more control of both the rate of descent and the touchdown point.
- Reduce Aircraft Weight. Again, if there is a choice, a lighter aircraft is better than a heavy one. Some aircraft, such as the C130 may be able to jettison cargo. Burning off, or dumping excess fuel, is another option for reducing weight but not all aircraft, especially short haul aircraft, have the ability to dump fuel. A lighter aircraft allows a lower approach speed and will likely be more buoyant facilitating the evacuation.
- Configuration - Gear. Gear up is the optimum configuration for ditching.
- Configuration - Flap. Likewise, most manufacturers will recommend that the maximum available slat/flap configuration be used to allow minimum approach speed. An element of judgement is required here as an intermediate flap setting allows a compromise between the benefits of lowest speed and best forward visibility and the amount of flare rotation required. With all engines out, there may be limited hydraulic power. (Note that on many modern generation aircraft, with all engines failed and the RAT deployed, the control law reverts to Alternate Law without protections. Speed must be maintained right down to the flare as in this control law configuration there is no automated stall protection.)
- Prepare the Cabin. In keeping with the time available:
- loose items should be secured or removed from the flight deck - at impact, loose items may fly around causing injuries and, after ditching, loose items may float and obstruct evacuation.
- Any available clothing items should be worn (to improve chances of survival in the water) and a life jacket put on.
- Again, time permitting, the cabin should be prepared and the passengers fully briefed. Life jackets should be donned by all, but not inflated. A reminder to passengers not to inflate their life jackets is extremely important.
- Locate and consider the deployment of any life rafts carried and/or the plans for the detachment of slides, which will be used as floatation devices, to prevent their loss.
- MAYDAY. Distress calls should be made on all appropriate frequencies. If in a radar environment, a MAYDAY on the ATC frequency should suffice. Use the emergency codes on the transponder if time allows. In a non radar environment such as in oceanic airspace, distress calls should be made on 121.5, enroute frequencies such as 123.45 and on the oceanic HF frequencies or via data link. As much information as practical should be transmitted inclusive of intentions and the most accurate position information that you can provide.
- Direction of Ditching. Determine the best direction for ditching. In a confined space such as a river, there will be no choice other than the axis of the river - if possible, choose the best into wind option unless there is a compelling reason for landing in the other direction. In open water, the determination of optimum ditching heading becomes more complicated:
- In ideal conditions (smooth water or very long swells) land into the wind. This will ensure the minimum possible touchdown speed and, therefore, the least impact damage.
- If the swell is more severe, inclusive of breaking waves, it is more advisable to ditch along the swell accepting the crosswind and the higher touchdown speed. This profile will minimize the potential for nosing into the face of an advancing wave. Considerable drift correction may be necessary to maintain a track along the swell in a strong crosswind. The best touchdown point is on the top of the swell with the second best on the back of the swell. Try to avoid the advancing face of the swell.
- In extremely strong winds, a compromise will likely be required. In this case landing somewhat across the swell and into the wind to the extent possible is the best option. Touchdown on the receding face of the swell is the preferable choice.
- At night, judging the wave motion is very difficult unless there is good illumination such as a full moon. In the absence of visual cues and with power available, flying low over the water on various headings can help determine the best ditching direction. In general, the heading which achieves a combination of the lowest ground speed and the smoothest ride and does not run into the face of the primary swell will be the best ditching course.
- Lighting: At night, prudent use of internal and external lights is critical. Minimize the cockpit lighting to maximize your night vision. Use landing and taxi lights prudently as, in some circumstances, they may actually make the situation worse by creating visual illusions and reducing night vision.
- Buoyancy. Close all valves below the waterline. [The A320 has a "Ditching Push Button" - selecting the ditching push button to ON in one selection closes all of the valves below the waterline (safety valve, outflow valves, ram air inlet) to minimize leakage and maximize buoyancy]
- Emergency Generator: On aircraft equipped with a Ram Air Turbine (RAT), the RAT should have automatically deployed with a double engine failure, and the generator should already on line. The RAT provides hydraulic power for both the flight controls and for the emergency generator. The RAT will have a minimum operating speed (140 knots in the A320) - were it to stall, you would lose hydraulics (and flight controls as a consequence). Where the cause of the double engine failure is not fuel exhaustion, the APU is also a source of electrical power.
- GPWS: Consider switching off the GPWS (and other audio warnings), at about 2000 ft, to prevent nuisance warnings as the gear will be up.
- High Wing Aircraft(e.g. C130). High wing aircraft settle lower in the water after ditching, and most of the fuselage will be submerged, making evacuation more difficult. Some checklists call for the removal of roof escape hatches in the event of a forced landing; this is because the impact forces may distort the aircraft frame and make it difficult for hatches to be opened. However, in the case of a ditching, do not remove roof escape hatches at the front of the aircraft (e.g. flight deck) until after the aircraft has settled on the water because, on ditching, the aircraft nose may "bob" down under the water as the aircraft comes to a halt completely submerging the flight deck and allowing water through any open hatches.
- Descent Rate: If power is available, use it to set up the minimum possible descent rate to your touchdown point (200 fpm or less). If power is not available, establish best glide speed (best lift over drag speed) and accept the resulting rate of descent. In both cases, just above the water, flare to the manufacturer's recommended touchdown attitude and hold that attitude to (and during) the touchdown. Touchdown should occur power off. Remember that the flare height will be slightly lower than for a normal landing because the gear is retracted. It is imperative that the aircraft be flown onto the water and NOT stalled.
- "Brace Brace". A call on the cabin/public address system should be made, typically at 200 ft, to warn crew and passengers of imminent impact with the surface and to about the "Brace" position. Although a flight crew function, the cabin crew must be prepared to give this call as appropriate.
- Touchdown: The optimum attitude for touchdown in most aircraft types is approximately 10 degrees nose up. Most AFMs or Ops Manuals will quote an ideal pitch angle to rotate to in the flare and it may not be the one normally used for a landing even at an equivalent flap/slat setting - it is a good idea to be aware of this before the event!
- Wings Level. Ensure that the wings are as level as possible at touchdown. Failure to do so could well result in digging in a wing and cartwheeling. Anticipate that there will probably be more than one touchdown, generally the second will be more violent than the first.
- Shutdown: At touchdown, shut down the engines and, when the aircraft comes to a stop, activate the Engine and APU Fire suppression systems.
- Evacuation: Once the aircraft has come to a complete stop, initiate the evacuation. The expected attitude of the aircraft in the water is almost always "nose up" so that the rear doors will not be useable for evacuation. Ensure all available survival gear is carried off of the aircraft. Whenever possible, link all of the rafts together to maximize the visual target for the search parties.
Post Ditching Survival Aspects
Many aspects of post ditching survival are covered by the actions described above. The environment the survivors will now find themselves in will be hostile. Continued survival will depend on the water and air temperature, the wind and sea state, the physical condition of the survivors, clothing worn, and the availability of survival equipment amongst many other things. Swift location and rescue are therefore vital.
- Position. Transmit location coordinates repeatedly on the final descent.
- Shipping. Survival post ditching will depend on how quickly you are picked up. Locate shipping, visually or using the radar, and try to ditch close to a ship. If there is a ship in the vicinity, touching down beside and slightly ahead is your best option as large vessels can take a considerable distance to slow down and are not manoeuvrable enough to take immediate avoiding action should you touch down right in front.
- Aircraft. Other aircraft may be able to follow the ditching aircraft in the descent and maintain visual contact with the ditched aircraft and radio contact with controlling authorities and other aircraft until the limit of endurance is reached.
Flight crew cannot realistically practice ditching in the simulator because there is limited if any data to programme the simulator. Training is limited to scenario based discussion and realistic practical ditching drills, ideally conducted in the sea using equipment carried on the aircraft type concerned - and in cold water!