SML was fitted with an EFIS system with a single display screen and a two-axis autopilot. This EFIS was capable of displaying GPS moving map, synthetic terrain and terrain proximity warnings.
The EFIS was not certificated and therefore not permitted to be used as a primary means of navigation, however, the system could be used as an aid to primary navigation, ie, as a map and compass.
During the investigation it was discovered the moving map display did not accurately display the 3717 ft spot height for Mt Duppa. The spot height was positioned at a join in the maps and the ‘3’, if not looked at carefully, could have been read as a ‘1’, making the spot height seem to be 1717 ft, not the 3717 ft it should be.
There was an additional error affecting the EFIS terrain display and warnings. An error of approximately 600 ft existed between the actual terrain height and the modelled terrain height in the terrain database. This error led to the EFIS displaying terrain indications associated with the modelled terrain of approximately 600 feet lower than the actual terrain.
Given the errors found in the EFIS system database, the pilot may have considered he was sufficiently clear of the terrain ahead, when he was not. Approaching Mt Duppa the pilot should have received a visual warning from the EFIS that he would not clear the terrain ahead, however, due to the system inaccuracies the display indicated he was clear.
All of these inaccuracies, however, would not have materially impacted the flight if the pilot had remained clear of cloud.