Index   435 -- Page 436 -- 437

AIM                                                                                                        12/10/15


                                                     FIG 6-3-5
                                           Wind-Swell-Ditch Heading



                                                   DIRECTION OF
                                                   SWELL MOVEMENT

                                                                                                   BEST

                                GOOD
                                                                               FAIR
                                                   GOOD
                                         Landing parallel to the major swell


                                GOOD !!                                      POOR!!!


                                   KS     IDE                               FACE
                               BAC
                                         Landing on the face and back of swell



  a. A successful aircraft ditching is dependent on              6. Secondary Swells. Those swell systems of
three primary factors. In order of importance they are:     less height than the primary swell.
      1. Sea conditions and wind.                               7. Fetch. The distance the waves have been
                                                            driven by a wind blowing in a constant direction,
      2. Type of aircraft.                                  without obstruction.
      3. Skill and technique of pilot.                          8. Swell Period. The time interval between the
  b. Common oceanographic terminology.                      passage of two successive crests at the same spot in
                                                            the water, measured in seconds.
     1. Sea. The condition of the surface that is the
result of both waves and swells.                                 9. Swell Velocity. The speed and direction of
                                                            the swell with relation to a fixed reference point,
     2. Wave (or Chop). The condition of the                measured in knots. There is little movement of water
surface caused by the local winds.                          in the horizontal direction. Swells move primarily in
    3. Swell. The condition of the surface which            a vertical motion, similar to the motion observed
has been caused by a distance disturbance.                  when shaking out a carpet.

     4. Swell Face. The side of the swell toward the             10. Swell Direction. The direction from which
observer. The backside is the side away from the            a swell is moving. This direction is not necessarily the
observer. These definitions apply regardless of the         result of the wind present at the scene. The swell may
direction of swell movement.                                be moving into or across the local wind. Swells, once
                                                            set in motion, tend to maintain their original direction
    5. Primary Swell. The swell system having the           for as long as they continue in deep water, regardless
greatest height from trough to crest.                       of changes in wind direction.


6-3-4                                                                             Distress and Urgency Procedures