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Ditching: Rotary Wing Aircraft

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Category: General General
Content source: SKYbrary SKYbrary
Content control: EUROCONTROL EUROCONTROL

Definition

Emergency Landing of an Aircraft on Water.

A Hazardous Maneouvre

Ditching an aircraft into the sea, a river, or a lake, is an extremely hazardous manouevre 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 and, if the crew and passengers survive the ditching then, even with protective clothing and equipment, they may die of hypothermia before they are rescued.

Scenarios

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;
  • Fuel Loss: A fuel leak that results in insufficient fuel to reach a runway;
  • Multiple Engine Failure: Failure of multiple engines - fuel exhaustion, fuel contamination, volcanic ash encounter, multiple bird strike are all possible causes.

Techniques for Ditching an Aircraft

The following is a list of generally accepted 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. Military pattern aircraft may be able to jettison cargo; most civil pattern aircraft (depending on why the water is the only choice) may be able to burn off or dump fuel. A lighter aircraft allows a lower approach speed and will likely be more buoyant facilitating the evacuation.
  • Gear Up. Gear up is the optimum configuration for ditching. Likewise, most manufacturers will recommend that the maximum available slat/flap configuration be used to allow minimum approach speed.
  • Prepare 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).
  • 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.
  • Shipping. 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.
  • Direction. 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. c) 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.

8) 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. 9) 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. 10) 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, maintain the appropriate airspeed as accurately as possible 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 as the gear is retracted. It is imperative that the aircraft be flown onto the water and NOT stalled. 11) 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 likely be more than one touchdown, generally the second will be more violent than the first. 12) Once the aircraft has come to a complete stop, initiate the 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.

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