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OPERATIONS IN OPEN SEAS
Open sea operations are very risky and should be avoided if possible. If an open sea landing cannot be avoided, a thorough reconnaissance and evaluation of the conditions must be performed to ensure safety. The sea usually heaves in a complicated crisscross pattern of swells of various magnitudes, overlaid by whatever chop the wind is producing. A relatively smooth spot may be found where the cross swells are less turbulent. Both a high and a low reconnaissance are necessary for accurate evaluation of the swell systems, winds, and surface conditions.
DEFINITIONS
When performing open sea operations, it is important to know and understand some basic ocean terms. A thorough knowledge of these definitions allows the pilot to receive and understand sea condition reports from other aircraft, surface vessels, and weather services.
Fetch—An area where wind is generating waves on the water surface. Also the distance the waves have been driven by the wind blowing in a constant direction without obstruction.
Sea—Waves generated by the existing winds in the area. These wind waves are typically a chaotic mix of heights, periods, and wavelengths. Sometimes the term refers to the condition of the surface resulting from both wind waves and swells.
Swell—Waves that persist outside the fetch or in the absence of the force that generated them. The waves have a uniform and orderly appearance characterized by smooth, regularly spaced wave crests.
Primary Swell—The swell system having the greatest height from trough to crest. Secondary Swells—Swell systems of less height than the primary swell.
Swell Direction—The direction from which a swell is moving. This direction is not necessarily the result of the wind present at the scene. The swell encountered may be moving into or across the local wind. A swell tends to maintain its original direction for as long as it continues in deep water, regardless of changes in wind direction.
Swell Face—The side of the swell toward the observer. The back is the side away from the observer.
Swell Length—The horizontal distance between successive crests.
Swell Period—The time interval between the passage of two successive crests at the same spot in the water, measured in seconds.
Swell Velocity—The velocity with which the swell advances in relation to a fixed reference point, measured in knots. (There is little movement of water in the horizontal direction. Each water particle transmits energy to its neighbor, resulting primarily in a vertical motion, similar to the motion observed when shaking out a carpet.)
Chop—A roughened condition of the water surface caused by local winds. It is characterized by its irregularity, short distance between crests, and whitecaps.
Downswell—Motion in the same direction the swell is moving.
Upswell—Motion opposite the direction the swell is moving.
If the swell is moving from north to south, a seaplane going from south to north is moving upswell.
SEA STATE EVALUATION
Wind is the primary cause of ocean waves and there is a direct relationship between speed of the wind and the state of the sea in the immediate vicinity. Windspeed forecasts can help the pilot anticipate sea conditions. Conversely, the condition of the sea can be useful in determining the speed of the wind. Figure 8-1 on the next page illustrates the Beaufort wind scale with the corresponding sea state condition number. While the height of the waves is important, it is often less of a consideration than the wavelength, or the distance between swells. Closely spaced swells can be very violent, and can destroy a seaplane even though the wave height is relatively small. On the other hand, the same seaplane might be able to handle much higher waves if the swells are several thousand feet apart. The relationship between the swell length and the height of 8-2 the waves is the height-to-length ratio [Figure 8-2]. This ratio is an indication of the amount of motion a seaplane experiences on the water and the threat to capsizing. For example, a body of water with 20-foot waves and a swell length of 400 feet has a height-tolength ratio of 1:20, which may not put the seaplane at risk of capsizing, depending on the crosswinds. However, 15-foot waves with a length of 150 feet produce a height-to-length ratio of 1:10, which greatly increases the risk of capsizing, especially if the wave is breaking abeam of the seaplane. As the swell length decreases, swell height becomes increasingly critical to capsizing. Thus, when a high swell height-to-length ratio exists, a crosswind takeoff or landing should not be attempted. Downwind takeoff and landing may be made downswell in light and moderate wind; however, a downwind landing should never be attempted when wind velocities are high regardless of swell direction. When two swell systems are in phase, the swells act together and result in higher swells. However, when two swell systems are in opposition, the swells tend to cancel each other or “fill in the troughs.” This provides a relatively flat area that appears as a lesser concentration of whitecaps and shadows. This flat area is a good touchdown spot for landing.
[Figure 8-3]
Sea surface smooth and mirror-like Scaly ripples, no foam crests Small wavelets, crests glassy, no breaking Large wavelets, crests begin to break, scattered whitecaps Small waves, becoming longer, numerous whitecaps Moderate waves, taking longer form, many whitecaps, some spray Larger waves, whitecaps common, more spray Sea heaps up, white foam streaks off breakers Moderately high, waves of greater length, edges of crests begin to break into spindrift, foam blown in streaks High waves, sea begins to roll, dense streaks of foam, spray may reduce visibility Very high waves, with overhanging crests, sea white with densely blown foam, heavy rolling, lowered visibility Exceptionally high waves, foam patches cover sea, visibility more reduced Air filled with foam, sea completely white with driving spray, visibility greatly reduced Calm, glassy 0 Calm, rippled 0 – 0.3 Smooth, wavelets 0.3-1 Slight 1-4 Moderate 4-8 Rough 8-13 Very rough 13-20 High 20-30 Very high 30-45 Phenomenal 45 and over 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 10 11 12 Less than1 1-3 4-6 7-10 11-16 17-21 22-27 28-33 34-40 41-47 48-55 56-63 64 and over Beaufort Number Wind Velocity (Knots) Calm Light Air Light Breeze Gentle Breeze Moderate Breeze Fresh Breeze Strong Breeze Near Gale Gale Strong Gale Storm Violent Storm Hurricane Wind Description Sea State Description Term and Height of Waves (Feet) Sea State Condition Number
BEAUFORT WIND SCALE WITH CORRESPONDING SEA STATE CODES
Figure 8-1. Beaufort wind scale. 400 Feet 150 Feet 20 Feet 15 Feet Height-to-Length Ratio 1: 20 Height-to-Length Ratio 1: 10 Figure 8-2. Height-to-length ratio. 8-3 5. To determine the swell length or distance between crests in feet, multiply the square of the swell period by 5. For example, using a 6-second swell period, 62 multiplied by 5 equals 180 feet.
[Figure 8-4]
LOW RECONNAISSANCE
Perform the low reconnaissance at 500 feet to confirm the findings of the high reconnaissance and obtain a more accurate estimate of wind direction and velocity. If the direction of the swell does not agree with the direction noted at 2,000 feet, then there are two swell systems from different directions. The secondary swell system is often moving in the same direction as the wind and may be superimposed on the first swell system. This condition may be indicated by the presence of periodic groups of larger-than-average swells. The wind direction and speed can be determined by dropping smoke or observing foam patches, whitecaps, and wind streaks. Whitecaps fall forward with the wind but are overrun by the waves. Thus, the foam patches appear to slide backward into the direction from which the wind is blowing. To estimate wind velocity from sea surface indications, see figure 8-1.
SELECT LANDING HEADING
When selecting a landing heading, chart all observed variables and determine the headings that will prove the safest while taking advantage of winds, if possible. Descend to 100 feet and make a final evaluation by flying the various headings and note on which heading the sea appears most favorable. Use the heading that looks smoothest and corresponds with one of the possible headings selected by other criteria. Consider the position of the sun. A glare on the water during final approach might make that heading an unsafe option. Use caution in making a decision based on the appearance of the sea. Often a flightpath directly downswell appears to be the smoothest, but a landing on this heading could be disastrous.
SWELL SYSTEM EVALUATION
The purpose of the swell system evaluation is to determine the surface conditions and the best heading and technique for landing. Perform a high reconnaissance, a low reconnaissance, and then a final determination of landing heading and touchdown area.
HIGH RECONNAISSANCE
During the high reconnaissance, determine the swell period, swell velocity, and swell length. Perform the high reconnaissance at an altitude of 1,500 to 2,000 feet. Fly straight and level while observing the swell systems. Perform the observation through a complete 360º pattern, rolling out approximately every 45º. Fly parallel to each swell system and note the heading, the direction of movement of the swell, and the direction of the wind. To determine the time and distance between crests, and their velocity, follow these directions:
1. Drop smoke or a float light and observe the wind condition.
2. Time and count the passage of the smoke or float light over successive crests. The number of waves is the number of crests counted minus one. (A complete wave runs from crest to crest. Since the timing starts with a crest and ends with a crest, there is one less wave than crests.) Time and count each swell system.
3. Obtain the swell period by dividing the time in seconds by the number of waves. For example, 5 waves in 30 seconds equates to a swell period of 6 seconds.
4. Determine the swell velocity in knots by multiplying the swell period by 3. In this example, 6 seconds multiplied by 3 equals 18 knots. Resultant Wave Wave A Wave B Resultant Wave Wave A Wave B Figure 8-3.Wave interference. Swell Period Swell Velocity Swell Period x 3 knots Swell Length Swell Period2 x 5 Feet Time in Seconds Number of Waves Counted Figure 8-4. Rules of thumb to determine swell period, velocity, and length. 8-4 SELECT TOUCHDOWN AREA On final approach, select the touchdown area by searching for a null or smooth area in the swell system, avoiding rough areas if possible. When doing so, consider the conditions discussed in the following sections.
LANDING PARALLEL TO THE SWELL
When landing on a swell system with large, widely spaced crests more than four times the length of the floats, the best landing heading parallels the crests and has the most favorable headwind component. In this situation, it makes little difference whether touchdown is on top of the crest or in the trough.
LANDING PERPENDICULAR TO THE SWELL
If crosswind limits would be exceeded by landing parallel to the swell, landing perpendicular to the swell might be the only option. Landing in closely spaced swells less than four times the length of the floats should be considered an emergency procedure only, since damage or loss of the seaplane can be expected. If the distance between crests is less than half the length of the floats, the touchdown may be smooth, since the floats will always be supported by at least two waves, but expect severe motion and forces as the seaplane slows. A downswell landing on the back of the swell is preferred. However, strong winds may dictate landing into the swell. To compare landing downswell with landing into the swell, consider the following example. Assuming a 10-second swell period, the length of the swell is 500 feet, and it has a velocity of 30 knots or 50 feet per second. Assume the seaplane takes 890 feet and 5 seconds for its runout. Downswell Landing—The swell is moving with the seaplane during the landing runout, thereby increasing the effective swell length by about 250 feet and resulting in an effective swell length of 750 feet. If the seaplane touches down just beyond the crest, it finishes its runout about 140 feet beyond the next crest.
[Figure 8-5]
Landing into the Swell—During the 5 seconds of runout, the oncoming swell moves toward the seaplane a distance of about 250 feet, thereby shortening the effective swell length to about 250 feet. Since the seaplane takes 890 feet to come to rest, it would meet the oncoming swell less than halfway through its runout and it would probably be thrown into the air, out of control. Avoid this landing heading if at all possible. [Figure 8-6] If low ceilings prevent complete sea evaluation from the altitudes prescribed above, any open sea landing should be considered a calculated risk, as a dangerous but unobserved swell system may be present in the proposed landing area. Complete the descent and before-landing checklists prior to descending below 1,000 feet if the ceiling is low.
LANDING WITH MORE THAN ONE SWELL SYSTEM
Open water often has two or more swell systems running in different directions, which can present a confusing appearance to the pilot. When the secondary swell system is from the same direction as the wind, the preferred direction of landing is parallel to the primary swell with the secondary swell at some angle. When landing parallel to the primary swell, the two choices of heading are either upwind and into the secondary swell, or downwind and downswell. The heading with the greatest headwind is preferred; however, if a pronounced secondary swell system is present, it may be desirable to land downswell to the secondary swell system and accept some tailwind component. The risks associated with landing downwind versus downswell must be carefully considered. The choice of heading depends on the velocity of the wind versus the velocity and the height of the secondary swell.
[Figure 8-7]
Direction of Swell Movement Direction of Swell Movement Direction of Swell Movement Position of Swell Halfway Through Runout Position of Swell at End of Runout Position of Swell at Touchdown Figure 8-5. Landing in the same direction as the movement of the swell increases the apparent length between swell crests. Due to the rough sea state, landings should not be attempted in winds greater than 25 knots except in extreme emergencies. Crosswind limitations for each type of seaplane must be the governing factor in crosswind landings.
EFFECT OF CHOP
Chop consists of small waves caused by local winds in excess of 14 knots. These small waves ride on top of the swell system and, if severe, may hide the underlying swell system. Alone, light and moderate chop are not considered dangerous for landings.
NIGHT OPERATIONS
Night landings in seaplanes on open water are extremely dangerous with a high possibility of damage or loss of the seaplane. A night landing should only be performed in an extreme emergency when no other options are available. A night landing on a lighted runway exposes the seaplane to much less risk. Direction of Swell Direction of Swell Direction of Swell Position of Swell at Touchdown Position of Swell at End of Runout Position of Swell Halfway Through Runout Landing Heading Landing Heading Primary Swell Direction Primary Swell Direction Secondary Swell Direction Figure 8-6. Landing against the swell shortens the apparent distance between crests, and could lead to trouble. Figure 8-7. Landing heading in single and multiple swell systems. 8-6 If operating at night, equip the seaplane with parachute flares, smoke floats, glow sticks, or other markers.
SEA EVALUATION AT NIGHT
Before attempting a night landing, perform a sea state evaluation as described in previous sections. If an emergency occurs shortly after nightfall, a landing heading can be determined by estimating the current conditions from those conditions prevalent before nightfall. If the pilot has no information to form an estimate of the conditions, the information must be obtained from other sources or determined by the pilot from a sea state evaluation by flare illumination or moonlight. If near a ship, sea weather conditions and a recommended landing heading may be obtained from the ship. However, a landing heading based on such information is subject to error and should only be used as a last resort. A pilot evaluation is preferred and can be accomplished by performing the teardrop pattern night sea evaluation as follows:
1. Set a parachute flare and adjust the altitude so that the flare ignites at 1,700 feet. Altitude should be as close to 2,000 feet as possible.
2. After the drop, adjust altitude to 2,000 feet and maintain the heading for 45 seconds.
3. Turn back 220º, left or right, until the flare is almost dead ahead. The sea becomes visible after the first 70º of the turn is completed, allowing approximately 90 seconds for sea evaluation. Use standard rate turn (3º per second).
4. Immediately after passing the flare, if it is still burning, the pilot may circle to make additional evaluation during remaining burning time. If both pilot and copilot are present, the pilot should fly the seaplane and the copilot should concentrate on the sea evaluation. If only two flares are available and sea conditions are known or believed to be moderate, it may be advisable to dispense with the sea evaluation and use both flares for landing.
NIGHT EMERGENCY LANDING
A night landing should be performed only after exhausting all other options. Be sure all occupants are wearing life vests and secure loose items prior to touchdown. Remove liferafts and survival equipment from their storage containers and give them to those occupants closest to the exits. Prior to the landing pattern, unlatch the doors to prevent jamming that may be caused by airframe distortion from a hard landing. If time permits, make distress calls and activate the emergency locator transmitter.
LANDING BY PARACHUTE FLARE
When a landing heading has been determined and all emergency and cockpit procedures have been accomplished, the landing approach with the use of parachute flares is made as follows:
1. Establish a heading 140º off the selected landing heading.
2. Lower the flaps and establish the desired landing pattern approach speed.
3. As close to 2,000 feet above the surface as possible, set the parachute flare and adjust the altitude so the flare ignites at 1,700 feet.
4. Release the flare and begin a descent of 900 f.p.m. while maintaining heading for 45 seconds. If the starting altitude is other than 2,000 feet, determine the rate of descent by subtracting 200 feet and dividing by two. (For example, 1800 feet minus 200 is 1600, divided by 2 equals an 800 f.p.m. rate of descent).
5. After 45 seconds, make a standard rate turn of 3º per second toward the landing heading in line with the flare. This turn is 220º and takes approximately 73 seconds.
6. Roll out on the landing heading in line with the flare at an altitude of 200 feet. During the last two-thirds of the turn, the water is clearly visible and the seaplane can be controlled by visual reference.
7. Land straight ahead using the light of the flare. Do not overshoot. Overshooting the flare results in a shadow in front of the aircraft making depth perception very difficult. The best touchdown point is several hundred yards short of the flare. A rapid descent in the early stages of the approach allows a slow rate of descent when near the water. This should prevent flying into the water at a high rate of descent due to faulty depth perception or altimeter setting.
[Figure 8-8]
LANDING BY MARKERS
If parachute flares are not available, use a series of lighted markers to establish visual cues for landing. When a landing heading has been determined and all emergency and cockpit procedures are completed, use drift signals or smoke floats and perform the landing approach as follows: 1. Establish a heading on the reciprocal of the landing heading. 2. Drop up to 20 markers at 2 second intervals. 3. Perform a right 90º turn followed immediately by a 270º left turn while descending to 200 feet. 4. Slightly overshoot the turn to the final approach heading to establish a path parallel and slightly to the right of the markers. 8-7 5. Establish a powered approach with a 200 f.p.m. rate of descent and airspeed 10 percent to 20 percent above stall speed with flaps down, as if for a glassy water landing. 6. Maintain the landing attitude until water contact, and reduce power to idle after touchdown. Do not use landing lights during the approach unless considerable whitecaps are present. The landing lights may cause a false depth perception.
[Figure 8-9]
EMERGENCY LANDING UNDER INSTRUMENT CONDITIONS
When surface visibilities are near zero, the pilot has no alternative but to fly the seaplane onto the water by instruments. A landing heading can be estimated from forecasts prior to departure, broadcast sea conditions, or reports from ships in the area. Obtain the latest local altimeter setting to minimize the possibility of altitude errors during the approach. Due to the high possibility of damage or capsizing upon landing, be sure all occupants have life vests on and secure all loose items prior to touchdown. Remove liferafts and survival equipment from their storage containers and give them to those occupants closest to the exits. Prior to the landing pattern, unlatch doors to prevent jamming caused by airframe distortion from a hard landing. If time permits, transmit a distress call and activate the emergency locator transmitter. After choosing a landing heading, establish a final approach with power and set up for a glassy water landing. Establish a rate of descent of 200 f.p.m. and maintain airspeed 10 to 20 percent above stall speed with flaps down. Establish the landing attitude by referring to the instruments. Maintain this approach until the seaplane makes contact with the water, or until visual contact is established. 140° 220° 73 Seconds 45 Seconds 200 Feet Touchdown Zone 2,000 Feet Landing Heading Figure 8-8. Landing by parachute flare. Landing Heading Touchdown Zone 200 f.p.m. Rate of Descent 10% to 20% Above Stall Speed. Flaps Down 90° 270° 200 Feet Figure 8-9. Landing by markers.
ESCAPING A SUBMERGED SEAPLANE
If a seaplane capsizes, it is absolutely essential that both pilot and passengers understand how to exit the seaplane and find their way safely to the surface. Pilots should become thoroughly familiar with possible escape scenarios and practice to the extent possible so that they will be able to react instantly in an emergency. Passengers can not be expected to have any prior training in water survival, and an actual emergency is not a good time to try to instruct them. Therefore, a complete briefing before takeoff is very important. At a minimum, the portions of the passenger briefing that deal with escaping from the seaplane in an emergency should cover orientation, water pressure issues, the use of flotation equipment, and both normal and unusual methods of leaving the seaplane.
ORIENTATION
Many of those who have survived seaplane accidents emphasize how disorienting this situation can be. Unlike the clear water of a swimming pool, the water around a seaplane after an accident is usually murky and dark, and may be nearly opaque with suspended silt. In most cases the seaplane is in an unusual attitude, making it difficult for passengers to locate doors or emergency exits. In a number of cases, passengers have drowned while pilots have survived simply because of the pilots’ greater familiarity with the inside of the seaplane. Use the preflight briefing to address disorientation by helping passengers orient themselves regardless of the seaplane’s attitude. Help the passengers establish a definite frame of reference inside the seaplane, and remind them that even if the cabin is inverted, the doors and exits remain in the same positions relative to their seats. Also, brief passengers on how to find their way to the surface after getting clear of the seaplane. Bubbles always rise toward the surface, so advise passengers to follow the bubbles to get to the surface.
WATER PRESSURE
The pressure of water against the outside of the doors and windows may make them difficult or impossible to open. Passengers must understand that doors and windows that are already underwater may be much easier to open, and that it may be necessary to equalize the pressure on both sides of a door or window before it will open. This means allowing the water level to rise or flooding the cabin adjacent to the door, which can be very counter-intuitive when trapped underwater.
FLOTATION EQUIPMENT
Personal flotation devices (PFDs) are highly recommended for pilots and all passengers on seaplanes. Since the probability of a passenger finding, unwrapping, and putting on a PFD properly during an actual capsizing is rather low, some operators encourage passengers to wear them during the starting, taxiing, takeoff, landing, and docking phases of flight. Not all PFDs are appropriate for use in aircraft. Those that do not have to be inflated, and that are bulky and buoyant all the time, can be more of a liability in an emergency, and actually decrease the wearer’s chances of survival. Many of the rigid PFDs used for water recreation are not suitable for use in a seaplane. In general, PFDs for aircraft should be inflatable so that they do not keep the user from fitting through small openings or create buoyancy that could prevent the wearer from swimming downward to an exit that is underwater. Obviously, once the wearer is clear of the seaplane, the PFD can be inflated to provide ample support on the water. The pretakeoff briefing should include instructions and a demonstration of how to put on and adjust the PFD, as well as how to inflate it. It is extremely important to warn passengers never to inflate the PFD inside the seaplane. Doing so could impede their ability to exit, prevent them from swimming down to a submerged exit, risk damage to the PFD that would make it useless, and possibly block the exit of others from the seaplane.
NORMAL AND UNUSUAL EXITS
The briefing should include specifics of operating the cabin doors and emergency exits, keeping in mind that this may need to be done without the benefit of vision. Doors and emergency exits may become jammed due to airframe distortion during an accident, or they may be too hard to open due to water pressure. Passengers should be aware that kicking out a window or the windshield may be the quickest and easiest way to exit the seaplane. Because many seaplanes come to rest in a nose-down position due to the weight of the engine, the baggage compartment door may offer the best path to safety. In addition to covering these basic areas, be sure to tell passengers to leave everything behind in the event of a mishap except their PFD. Pilots should never assume that they will be able to assist passengers after an accident. They may be injured, unconscious, or impaired, leaving passengers with whatever they remember from the pilot’s briefing. A thorough briefing with clear demonstrations can greatly enhance a passenger’s chance of survival in the event of a mishap.
List below the other topics for Seaplane, Skiplane and Float Airplane types .
Seaplane Rules, Regulations, and Aids for Navigation
Water Characteristics and Seaplane Base Operations
Seaplane Operations – Preflight and Takeoffs
