Flight Safety: Rules for ditching light aircraft

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the gremline digest — ditching light aircraft

Ditching Light Aircraft

I’m glad to report that in over 50 years of flying I have never had to ditch an aircraft. I have had a few engine failures and managed successful forced landings, both on and off airfields. I have also survived two ejections into the sea. A ditching is a forced landing on water, so all the drills and skills you have learned during your regular practice forced landing exercises will apply if you are faced with putting your aircraft safely onto the water.

 

 Being forced to ditch your aircraft is probably the least likely emergency you will ever face, but you will only have one opportunity to get it right. Ditchings involving UK registered light aircraft are rare, but not unknown. The combined statistics for UK and USA registered light aircraft ditchings reveal two very interesting facts. First, 88% of controlled ditchings result in little or no injury to the aircraft occupants. There is no statistically significant difference between high wing and low wing aircraft. Second, half of those pilots and passengers who survive the water landing die before the rescue services get to them. It is obviously vital for anyone planning an over-water flight to consider their survival AFTER the ditching and to prepare and equip themselves and their aircraft for survival.
      The low survival rate following a successful ditching points to the need for private pilots to have a greater understanding of the problems of sea survival and ways in which they can improve their chances. “Sea Survival” is the subject of a separate article in Gremline so this vital aspect of a successful outcome to ditching a light aircraft will only be touched on lightly here.

 

 

The Basics
So, there you are, half way across the English Channel when your only engine coughs and loses power. Being a sensible pilot you are cruising at the highest altitude available to you, everyone on board is wearing clothing suitable for the environment
outside the aircraft, they are all wearing a life jacket they know how to use and everyone has their shoulder harness adjusted comfortably tight. If you are missing any of those items you have already reduced the chances of survival for yourself and your passengers. Denim jeans are probably the worst possible clothing to wear in any survival situation. Wet wool retains half of its dry insulating properties; wet cotton retains only 10% of its dry insulation.
      Make a MAYDAY call and switch your transponder to 7700. If you manage to restore engine power by switching tanks, selecting HOT carb air, undoing the mis-selection that caused the failure or whatever, you can cancel the MAYDAY and nobody will think badly of you. If you don’t manage to sort the problem then you are faced with a ditching.

 

Preparing to Ditch
You should be familiar with the performance figures for your particular aircraft. You know the best gliding speed, you have a good idea of the surface wind velocity from your pre-flight planning and you go into your forced landing drills without hesitation – following the same procedures as you have done during your regular practice forced landing over land. Your MAYDAY call should contain as much information as possible, but your first priority is to
FLY THE AIRCRAFT. Your MAYDAY call will follow exactly the same format as you use during your periodic ‘Practice Pan’ exercises. How often do you exercise the D&D Cell, and yourself, with a Practice Pan call? I use ‘PAT CASATNI’ as a memory aid: ‘Position And Time, Course And Speed, Altitude, Type of Aircraft, Nature of Distress, Intentions.’
      You should know how far your aircraft will glide per thousand feet, but it will not be very far so you are unlikely to have the option to glide to land. Looking at a few numbers gives an idea of the distance you may cover. If you are at 3000 feet and your aircraft has a best glide speed of 70 knots while descending at 500 feet per minute then you will cover 4.6 nautical miles in still air before you get to 1000 feet above the water and must concentrate on the landing. (Next time you are returning from a cross-country flight why not position yourself over the airfield, close the throttle, trim for best glide speed and note your stabilised rate of descent?) Now calculate your gliding range per thousand feet. Not very far, is it? A 1:10 glide ratio is not bad for the average GA single.
      During a forced landing on land you select a suitable field. Over the sea, look for a medium sized ship that is close to your present position. Big ships take ages to stop and it is unlikely that anyone on board will be looking out as their radar and autopilot takes them towards the horizon. Smaller ships are more likely to be under human control and someone on board may spot you if you ditch ahead of the ship and parallel to its track. Trawlers are ideal targets as there is usually somebody working on deck.
      If you were cruising at a sensible altitude you now have a few minutes to prepare for touchdown. Check that loose articles are stowed away. A suitcase lying on the back seat could break you neck on impact. Check that seats are firmly locked and that harnesses are tight. Passengers should remove and stow their headsets and glasses, if worn. Have you got a hand-held VHF set and/or a mobile phone in a sealed plastic bag stuffed into a pocket? You are forbidden to use your mobile phone while airborne, but it could be very handy after touchdown. Perhaps you should unlock a door, open or jettison the canopy. Details will depend on your aircraft type. Study of the Flight Manual or Pilot’s Operating Handbook should uncover specific advice. If you have plenty of time you might consider resetting your altimeter to the area QNH so as to give a more accurate indication of your height above the sea.
      By the time you get down to 2000 feet the direction of any swell will become obvious. The swell direction and the surface wind direction may be totally different. If there is an obvious swell running and the wind is not above about 20 knots then you should concentrate on touching down parallel to the swell and land along the crest or just behind the crest,
NOT in front of the crest. If the surface wind is particularly strong in comparison to your touchdown speed then it is probably better to land into wind rather than along the swell. It is worth remembering that the impact force on touchdown is proportional to the square of the speed. An aircraft touching down at 50 knots in calm windless conditions will have to dissipate 4 times as much kinetic energy as the same aircraft touching down at the same airspeed but landing into a 25 knot headwind. This excess of energy will have to be absorbed by the aircraft structure and those inside the aircraft.
      The following table gives an indication of the appearance of the sea in different wind speeds and the effects this will have on your direction of touchdown decision.

 

 

Facing the Ocean
If you are flying an aircraft with retractable gear then always leave the gear up. Beware of those types that have ‘automatic’ gear lowering systems that operates as you reduce your airspeed/throttle setting. This must be overridden. The use of flaps will vary from type to type, but general advice is to use not more than take-off flap on low wing aircraft and to use full flap, selected just prior to touchdown, on high wing aircraft. Selecting full flap too early will give you a steeper descent than is ideal. Brief everyone to cross their arms in front of their face and to remain in that position until the aircraft comes fully to rest in the water. It’s a good idea for the pilot to place a free forearm in front of the face just before impact. There will almost certainly be several impacts, with the first being most gentle.
      Hold the aircraft off the water to touchdown at a low, but controlled, speed. Do not stall in. The rear of the aircraft will probably touch the water first, with a relatively minor impact and the possibility of one or two skips. The aircraft will then pitch forward to the main impact. There will be a harsh deceleration and the nose will pitch into, and probably under, the surface. The windscreen may implode. If you are in a high wing aircraft it may be impossible to fully open a door until the cabin is almost full of water. If the aircraft remains upright then it will tend to float with the wings just below the surface so the cabin of a low winged aircraft will probably be above the surface while the cabin of a high winged aircraft will be at least partially submerged.

 

 

Waiting for Rescue
You should have briefed your passengers on the method and sequence of exit from the cabin. The shock of ditching and the physiological ‘cold shock’ of being immersed in water will affect everyone’s reactions. Concentrate on getting everyone out of the aircraft as quickly as possible. It is vital not to inflate lifejackets until you are out of the cabin. Stay together in the water.
      If you have a life raft in the cabin your pre-flight briefing should have nominated somebody to be responsible for its removal and inflation. The strongest and fittest person in the group should be first into the life raft to assist others from the water. It is much easier to drag someone into the dinghy than it is to try to push them in from the water.
      If you do not have a life-raft to board then it may be possible to lash your lifejackets together so that you are in a close, inward-facing group. At least hold onto each other. Place any children or weaker people in the middle of the huddle. This will provide more security for everyone and may help to reduce heat loss as you wait for rescue. It is imperative to take all survival actions as soon as you get into the water. No matter what the season of the year, the water around the UK is always cold and everyone will soon lose the use of their hands and their ability to perform even the simplest of manual tasks. You, as captain of the aircraft, are responsible for the safety of your passengers. Do not hesitate to take command of the situation and to issue clear instructions while encouraging everyone that you will be rescued. You must reduce heat loss as far as possible. The major heat loss areas are your head, the sides of your chest and your groin. Use the life-jacket hood to reduce loss from your head. Clutch your arms against the sides of your chest and cross your hands over your chest. Raise your knees, cross your feet and keep your thighs together.
      We can now assume that you have joined the 88% of successful ditchings. How to avoid becoming part of the 50% of ditched GA aircraft occupants who die before the rescuers can arrive on the scene is the subject of our article on ‘Sea Survival’ (qv).

 

 

Ditchings are survivable. Survival and rescue are in your own hands.

 

 Several UK companies supply sea survival equipment for purchase or rental and some can also provide practical training for groups in your local swimming pool. If you make regular flights over the sea a practice session in a swimming pool with expert tuition is a very good investment.
      A final thought from Darrol Stinton, an extremely experienced test pilot: “Take heart; what you prepare for rarely happens.”

 

 Recommended reading:
UK CAA General Aviation Safety Sense Leaflet 21 –“Ditching”

“Survival for Aircrew” by Sarah-Jane Prew, available from our Bookshop.

 

 

 

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Text and Photographs © 2007 Gremline & Hill House Publications, unless otherwise stated.

 

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Wind Speed

Appearance of Sea

Effect on Ditching Direction

0-6 knots
(Beaufort 0-2)

Glassy calm / Small ripples.

Height judgement difficult. Ditch parallel to swell.

7-10 knots
(Beaufort 3)

Small waves with few small white caps.

Ditch parallel to swell.

11-21 knots
(Beaufort 4-5)

Larger waves with many white caps.

Use headwind component to reduce impact speed but still ditch parallel to swell.

22-33 knots
(Beaufort 6-7)

Medium to large waves with foam. Crests and many white caps.

Ditch into wind on the crest, or on the down slope behind the crest.

34 knots & above
(Beaufort 8+)

Large waves with foam streaks. Tumbling wave crests.

Ditch into wind on the crest, or on the down slope behind the crest. Do not fly into the face of the wave.