Any Great Circle Track
crossing the equator will cross the equator again at the exact opposite side of
the earth, i.e. if it crosses at the Greenwich Meridian it will cross again at
the Greenwich Ante-Meridian. The longitudes of both crossing points will have
opposite signs, i.e. one will be West and the other East and they will add up
to 180°.
Therefore, if it crosses at 030°W it will cross again at 180° - 030° = 150° and
in the opposite hemisphere = 150°E.
This is a Great Circle Track which is subject to convergency and which starts
at 035°T (in a north-EASTERLY direction) where it crosses the equator at 030°W.
At 150°E the GCT will have changed from a north-easterly track to a south
easterly track over 180° of longitude.
The point where the track is either due East or due West is also the point
where the track reaches its highest latitude, which also happens to be at the
mid-point, i.e. Change of Longitude to the mid-point = 90°
030°W + 90° (Easterly) = 060°E