ANSP info/procedural error involving a Boeing 767-338ER, VH-OGF, Denpasar, on 14 May 1996

An Australian registered B767 aircraft arrived at Denpasar (Bali) aerodrome at night, and amid several active thunderstorms. The weather forecast indicated fine weather, but on arrival, Instrument Meteorological Conditions (IMC) prevailed. Inside 10NM from the aerodrome, the crew needed to avoid three thunderstorms which made instrument approaches difficult.

There was no advice to aircrew of the presence and intensity of the thunderstorms on the 'Meteorological Information to Aircraft in Flight' (VOLMET) or the Automatic Terminal Information Service (ATIS). Air traffic control did not provide any updates on such storms.

Navigation was made more difficult as the main aerodrome navigational aids were overdue for calibration and the relevant NOTAM indicated they were to be used 'with caution'. The crew made two missed approaches before successfully landing at the destination. The Bali VOR approach aid had been reported to be up to 12 degrees out of alignment, but air traffic control were able to have a ground technician ensure that it remained within ground tolerances to permit instrument approaches in IMC.

The investigation revealed that the aircraft engaged in performing the flight testing of the Bali navigational aids had been placed unserviceable the day before it was due to commence testing at Bali. The aids were to be rescheduled for testing as a priority, once the aircraft was serviceable.

Safety Action

As a result of the investigation, air traffic controllers were reminded by their local air traffic services management, of their responsibility in providing accurate weather updates to aircrew. Controllers were also reminded of the requirement to provide such weather information on the ATIS and VOLMET services.

On request from Indonesian ATS management, Australian operators were asked to report any discrepancies in the navigational aids to air traffic control by radio at the time of the occurrence, so that ground technicians can investigate the cause immediately.