Ditching: Fixed Wing Aircraft
Ditching: Fixed Wing Aircraft
The controlled emergency landing of an aircraft on water.
A Difficult and Demanding Manoeuvre
Ditching an aircraft into the sea, a river, or a lake, is a manoeuvre that, by definition, cannot be practiced and may be extremely hazardous. It is only contemplated when no other realistic option remains in an emergency. For fixed wing this may be because there is a growing fire onboard and/or it is not possible to reach a runway, or succeed with an approach to those runways within reach and the situation does not favour or even allow an attempt at an off-airport forced landing.
Even if the Sea State is slight, there is a strong possibility that a small aircraft will fail to remain upright and/or will sink rapidly and that a large fixed wing aircraft will suffer a loss of structural integrity on impact with the water surface. Limited available evidence suggests that such structural failure may be in the area of the centre fuselage and in the vicinity of the rear pressure bulkhead. If the occupants survive the ditching then, even with the benefit of protective clothing and equipment, in cold waters they may succumb to cold shock or hypothermia before they are rescued.
A controlled ditching might be made in anticipation of a loss of control or its actual onset. In the case of most multi-engined fixed wing aircraft, this will be a consequence of the failure of more than 50% of the available engines because of:
- Fuel Contamination
- Fuel Exhaustion
- Fuel Starvation
- Ingestion into more than one engine of large birds
- Ingestion of high density volcanic ash
Other potential causes of an impending loss of control which could prompt a decision to ditch include uncontrollable and developing fire or structural failure and, for rotary wing aircraft over water, indications of imminent power transmission failure or loss of rotor integrity for which the procedural response is 'Land Immediately'.
Considerations and Techniques for Ditching a Fixed Wing Aircraft
The following is a list of generally accepted considerations and techniques for ditching that should be applicable to virtually any fixed wing aircraft type.
Facilitating Rescue after ditching
- Position. Transmit location coordinates repeatedly on the final descent. If fitted and possible, consider activating ELTs during the descent to ensure they are transmitting prior to impact. Ensure Transponder code is set (mode S or A/C as available.)
- 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.
Achieving the Ditching
- 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 point at which touchdown is made.
- Reduce Aircraft Weight. Again, if there is a choice, a lighter aircraft allows a lower approach speed and will probably remain afloat higher in the water and for longer thus facilitating occupant evacuation. Burning off or dumping fuel also has the advantage of increasing buoyancy in some aircraft types by creating a larger air mass held within the fuel tanks.
- Configuration - Gear. Gear up is the optimum configuration for ditching.
- Configuration - Flap. Most manufacturers recommend the maximum deployment of available slats/flaps is desirable to minimise approach speed. However, judgement is required in this respect since an intermediate flap setting is likely to improve forward visibility and reduce the amount of rotation required to flare in return for some increase in airspeed. Without some or all engines functioning, there may be limited hydraulic power.
- Propeller Driven Aircraft - Protection of Passengers. Where possible, consider moving passengers away from seat rows in line with the propellers. If a “power on” approach is available the propellers may break up on touchdown and debris could penetrate the fuselage.
- Flight Envelope Protection With all engines off, as well as in many other major failure scenarios, Fly-By-Wire aircraft may revert to control laws with degraded or non existent flight envelop protection so that it becomes particularly important to control accurately the intentionally low airspeed on final approach.
- MAYDAY. Distress calls should be made on all appropriate frequencies - if in a radar environment, a MAYDAY on the ATC frequency in use should suffice. The emergency code should be selected on the transponder if powered. In a non radar environment distress calls should be made on 121.5, on the applicable HF frequencies or via data link. As much relevant information as possible should be given especially the most accurate position information possible.
- 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; the direction with the higher headwind component should be chosen unless there is a compelling reason otherwise. In open water, the determination of optimum ditching heading becomes more complex. sea state is of critical importance since unless it is calm, the chances are that the direction of the wind will differ from that of the swell.
- In ideal conditions (smooth water or very long swells) land into the wind. This will ensure the minimum possible touchdown speed and help minimise impact damage.
- Where the swell is more marked, it may be advisable to ditch along the swell accepting a crosswind component and the higher touchdown speed, thus minimising the potential for nosing into the face of the rising swell. 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. Aim to remain well clear of the advancing face of the swell.
- In extremely strong winds, a compromise may well 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 sea state is likely to be extremely difficult unless there is good overall 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 touchdown and does not run into the face of the swell will be the best ditching course.
- Lighting: At night, prudent use of both internal and external lights is critical. Minimising flight deck lighting will be important to maximise external night vision. Landing and taxi lights can in some circumstances actually make the situation worse by creating visual illusions and interfering with night vision.
- Buoyancy. Specified action to close all valves below the likely initial waterline after a successful ditching should be followed. Some aircraft have a 'Ditching Push Button' which closes all such valves to minimise water ingress to a fuselage which remains intact
- Emergency Generator: On aircraft equipped with a Ram Air Turbine (RAT), the RAT should have automatically deployed if all engines have failed. Depending upon the aircraft type, this will provide electrical power or hydraulic power for both the flight controls and for the emergency generator subject to the aircraft maintaining a nominated minimum airspeed, typically around 140 knots. The implications for aircraft control of going below whatever this speed is in an aircraft without any other power source should be carefully considered. Where the cause of an all-engines failure is not fuel exhaustion or starvation, the APU generator will usually be of the same capacity as a single engine generator.
- EGPWS: Consider de-activating the EGPWS (and possibly other audio warnings), by about 2000 feet asl since it will otherwise constitute a potential low height distraction due to retracted landing gear.
- High Wing Aircraft Escape Hatches Aircraft such as the BAe146 / Avro RJ or ATR42 will settle lower in the water after ditching than a low wing aircraft so that more of the fuselage will be submerged and evacuation potentially more difficult. Although some checklists call for the removal of roof escape hatches prior to a forced landing because impact forces may distort the aircraft frame and make them difficult to open, this should not be done prior to a ditching to preclude the risk of additional water ingress.
- Final Approach Rate of Descent: 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. 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. Select power off on touchdown unless manufacturer guidance indicates otherwise but achieving a gentle touchdown is usually more important than worrying about engine management.
- "Brace Brace". A call on the cabin/public address system should be made, typically at 200 feet, 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 circumstances dictate. Some manufacturers suggest the crew give a cabin PA call of “Take up ditching positions” or words to that effect at 1000’ to alert cabin crew who may be carrying out duties in the cabin, to return to their seats and strap in.
- Touchdown: The optimum attitude for touchdown in most aircraft types is approximately 10 degrees nose up. The AFM or Operations Manual will usually 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
- 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.
In the time available:
- All loose items should be secured, particularly in the flight deck - at impact, loose items may fly around causing injuries and once water enters the fuselage, loose items may float and impede occupant evacuation.
- Any available clothing items should be worn to improve chances of survival in the water.
- A briefing should be given to passengers, especially in respect of usable / unusable exits, to the extent that available time permits. Life jackets should be donned by all, but not inflated until outside the aircraft - a reminder in respect of the latter is important.
- If life rafts are carried, follow applicable procedures; re-brief procedures for detachable escape slides at exits for use as floatation devices.
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 usable for evacuation. Ensure all available survival gear is taken from the aircraft. Whenever possible, link all of the rafts together to maximize the visual target for the search parties.
Post Ditching Survival
Many aspects of post ditching survival are covered by the actions described above. Training and procedure may get your aircraft down into the water safely; leadership and strong mental attitude is needed to get out. The environment the survivors will now find themselves in will certainly be unfamiliar and unexpected and may be extremely hostile. Continued survival will depend on the water and air temperature, the wind and sea state, the physical and mental condition of individuals, the clothing worn and the availability of useful survival equipment amongst many other things. Swift location and rescue may well be of crucial importance. The references in 'Further Reading' below offer considerable discussion of the issues involved in survival following a ditching.
Training for Ditching and the Aftermath
Full Flight Simulator practice of ditching by pilots is impossible because there is no data with which to meaningfully program the simulator. Training is limited to scenario-based discussion of both the process of ditching and, for all aircrew, the emergency evacuation of an aircraft which has landed on water.
Examples of Fixed Wing aircraft Ditchings
- A320, vicinity LaGuardia New York USA, 2009 - On 15 January 2009, a United Airlines Airbus A320-200 approaching 3000 feet agl in day VMC following take-off from New York La Guardia experienced an almost complete loss of thrust in both engines after encountering a flock of Canada Geese . In the absence of viable alternatives, the aircraft was successfully ditched in the Hudson River about. Of the 150 occupants, one flight attendant and four passengers were seriously injured and the aircraft was substantially damaged. The subsequent investigation led to the issue of 35 Safety Recommendations mainly relating to ditching, bird strike and low level dual engine failure.
NOTE The Report of this Investigation contains considerable discussion about both the operational and airworthiness issues posed by the ditching of a large transport aircraft.
- AT72, en-route, Mediterranean Sea near Palermo Italy, 2005 - On 6 August 2005, a Tuninter ATR 72-200 was ditched near Palermo after fuel was unexpectedly exhausted en route. The aircraft broke into three sections on impact and 16 of the 39 occupants died. The Investigation found that insufficient fuel had been loaded prior to flight because the flight crew relied exclusively upon the fuel quantity gauges which had been fitted incorrectly by maintenance personnel. It was also found that the pilots had not fully followed appropriate procedures after the engine run down and that if they had, it was at least possible that a ditching could have been avoided.
- WW24, vicinity Norfolk Island South Pacific, 2009 - On 18 November 2009, an IAI Westwind on an aeromedical flight failed to achieve a landing at Norfolk Island after four night IMC approaches in poor weather and was then intentionally ditched offshore due to having insufficient fuel then remaining to reach the nearest alternate. The fuselage broke in two after the ditching but all six occupants escaped from the rapidly flooded fuselage before it sank and were eventually located and rescued. The situation which led to the ditching was attributed by the subsequent investigation to poor in flight decision making possibly affected by fatigue.
- NIM, manoeuvring, northern North Sea UK, 1995 - On 16 May 1995, an RAF Nimrod maritime patrol aircraft on a day VMC airworthiness function flight off the north east coast of Scotland following major maintenance suffered an uncontrollable fire in one of its four engines which subsequently spread to the adjacent engine and threatened the structural integrity and consequently the likely controllability of the aircraft. A successful ditching in the sea was subsequently carried out 3 nm from RAF Lossiemouth. All occupants successfully evacuated the aircraft, with three sustaining minor injuries.
- Waterproof Flight Operations, Flight Safety Foundation, September 2003.
- TP13822E - Survival in Cold Waters: Staying Alive, C. Brooks, TSB Canada, January 2003
- Life Rafts and Lifeboats: An Overview of Progress to Date, Chapter 9A of NATO RTO-AG-HFM-152 ‘Survival at Sea for Mariners, Aviators and Search and Rescue Personnel’, by C. Brooks, February 2008