Initial Approach Fix (IAF) ZACKS Intercept
A FIX is a point on a chart that is defined off of another point or Navaid. It is used to describe a place in space that we use for navigation. The FAA uses (5) Five letters to NAME each point or FIX. In this case, the fix is called ZACKS. ZACKS is also the Final Approach Fix which will be covered in the Profile View.
This FIX is defined off of TWO (2) VORTAC stations, GVO and RZS San Marcus. In order to determine when we arrive at this particular location while flying INBOUND on the GVO r-099°, we must tune our other VOR radio to RZS (San Marcus) and notice when we cross the 145° Radial of RZS. When we reach this point, we will be AT the Initial Approach Fix (IAF) ZACKS.
The LIGHTNING BOLT pointing to the interception reminds us that this point is defined by an intersection of two Navaid radials.
Below the (IAF) ZACKS INT line is GVO and an outstretched D. Inside this 'D' is the value 20.7. This represents 20.7 nautical miles from the reference Navaid, GVO VORTAC. The GVO tells us that the FIX is defined off of the Gaviota VORTAC.
LASTLY, we can define what the IAF is actually used for. Quite simply, the IAF is the point where you are said to be beginning the approach. By arriving at this point, you are starting your approach into the airfield as published. This is typically a point where Approach Control will vector you to start your approach. You may also report arriving at this position since you will normally begin changing altitudes from earlier assigned to published.