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 impor-
tant 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 direc-
tion 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 suc-
cessive 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, meas-
ured 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 irregu-
larity, 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 dis-
tance 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
Ch 08.qxd 8/25/04 11:27 AM Page 8-1
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 cap-
sizing. For example, a body of water with 20-foot
waves and a swell length of 400 feet has a height-to-
length 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 pro-
duce 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 concentra-
tion 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
Calm, rippled
0 – 0.3
Smooth, wavelets
0.3-1
Slight
Moderate
Rough
Very rough
High
Very high
Phenomenal
45 and over
Less than1
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.
Ch 08.qxd 8/25/04 11:27 AM Page 8-2
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 sys-
tem. 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, white-
caps, 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 pos-
sible 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 appear-
ance 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 deter-
mine 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 direc-
tion 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 multi-
plying 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 Period 2 x 5 Feet
Time in Seconds
Number of Waves Counted
Figure 8-4. Rules of thumb to determine swell period,
velocity, and length.
Ch 08.qxd 8/25/04 11:27 AM Page 8-3
SELECT TOUCHDOWN AREA
On final approach, select the touchdown area by
searching for a null or smooth area in the swell sys-
tem, 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 par-
allel 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 pre-
ferred. 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 increas-
ing 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 sea-
plane 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 second-
ary 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 care-
fully 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.
Ch 08.qxd 8/25/04 11:27 AM Page 8-4
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 cross-
wind 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 underly-
ing 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 run-
way 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
Landin
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.
Ch 08.qxd 8/25/04 11:27 AM Page 8-5
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 esti-
mate 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 pat-
tern, 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 possi-
ble, 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 approx-
imately 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 visi-
ble 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 set-
ting. [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 land-
ing 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.
Ch 08.qxd 8/25/04 11:27 AM Page 8-6
5. Establish a powered approach with a 200 f.p.m.
rate of descent and airspeed 10 percent to 20 per-
cent 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
Seconds
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.
Ch 08.qxd 10/25/04 2:37 PM Page 8-7
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 train-
ing 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 mini-
mum, 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 disorien-
tation 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 win-
dows 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 recom-
mended for pilots and all passengers on seaplanes.
Since the probability of a passenger finding, unwrap-
ping, 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 gen-
eral, PFDs for aircraft should be inflatable so that they
do not keep the user from fitting through small open-
ings or create buoyancy that could prevent the wearer
from swimming downward to an exit that is underwa-
ter. 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 impor-
tant 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 sub-
merged 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 brief-
ing with clear demonstrations can greatly enhance a
passenger’s chance of survival in the event of
a mishap.