On 19 March 2014 during a flight test for the issue of a Civil Aviation Safety Authority (CASA) Approved Test Officer (ATO) delegation, it was noted that the Flight Director (FD) bars were not giving the correct information to the flight crew.

The Beech 1900D aircraft registered VH-YOA flown for the test flight was fitted with an EFIS 84 and a KLN 90B GPS (GPS). During a second flight to try and isolate the issue, the crew found that when the GPS rescaled in the latter part of an RNAV approach, and the flight directors were selected, there was a discrepancy between the information provided by the FD, and that by the GPS. The company then flew a similar flight in another of their Beech 1900D aircraft and found a similar discrepancy occurred.

The operator sought clarification from the aircraft flight manual supplements, however the flight manual supplements did not give clear instruction regarding the selection of the FD bars during RNAV approaches.

It was confirmed that the flight directors provided accurate guidance during instrument landing system (ILS), VHF omnidirectional range (VOR) approaches, and long range navigation (LRN).

An independent avionics engineering check on the GPS installation found that the system was correctly wired. CASA advised that although the wiring in the aircraft complied with the foreign Supplemental Type Certificate (STC) it did not comply with the original manufacturer’s instructions.

As a Safety Action, the Chief Pilot issued a Flight Crew Directive, advising that flight directors were not to be used on RNAV approaches.

In addition, as the ATSB was unable to determine the reason for the discrepancy, they forwarded a copy to the foreign authority responsible for issuing the STC.


Aviation Short Investigations Bulletin - Issue 36