On 24 April 2015, a Bombardier DHC8-300 making an RNAV approach at Adelaide in IMC with the AP engaged went below the procedure vertical profile. An EGPWS ‘PULL UP Warning was triggered at 5½nm out and the approach was discontinued reportedly due to spurious instrument indications. The Investigation found that the premature descent had occurred when mode re-selection after a Flight Director dropout had been incorrect with VS active instead of VNAV. It was found that both pilots had assessed the ‘PULL UP Warning as spurious and a missed approach rather than the mandated terrain avoidance procedure had been flown.