JP 3-50 National Search and Rescue Manual Vol I - US Navy

1. The aircraft glide area shown in Figure 5-1 is a datum area,
since the aircraft has an equal likelihood of being anywhere
within that area. A maximum possibility area can be developed
using hours of fuel on board, wind speed and direction, glide
ratio, and time of departure. A vector representing wind
speed and direction is added to the departure point. The SMC
then determines the distance the aircraft could cruise from
the time of departure to the end of fuel endurance, to which
the possible glide distance is added. The SMC uses this as a
radius for the datum area. A similar approach can be used for
marine craft with fuel endurance in hours, maximum range at
cruising speed, and water drift forces. Figure 5-2 shows the
general method used to find a maximum possibility area.
2. Datum areas are usually large when the search object endurance
is great or many unknown factors exist. Extensive detective
work may be necessary to reduce this size to a reasonable
initial position, or the SMC may have to outline the datum
area based on other hypotheses. For instance, an aircraft may
be reported missing while flying in a defined operating area
or along a flight planned route, a fishing vessel may have
gone to particular fishing grounds, a private aircraft or
pleasure boat operating area may be
Figure 5-2. Maximum Area of Possibility
5-3