An airliner crashed several years ago when the crew mistakenly
descended to the initial approach altitude when cleared for the
approach several miles out. The CVR recorded the conversation between
the two pilots discussing whether or not that meant they could go down
to the IAF altitude (they had been cleared direct to the IAF not via a
feeder fix). The captain won the discussion and the aircraft hit a
ridgeline before the IAF. Unless established on a published segment of
the approach, the aircraft is not automatically cleared to descend.
Feeder fixes depicted on the approach plate are considered published
segments of the approach and when approach clearance is received, the
aircraft may descend to the MEA published for that feeder fix without
specific clearance.