A Fairchild Metro aircraft was flown below the glideslope during an approach into Brisbane when the pilot flying transitioned to a visual approach despite briefing and receiving clearance from air traffic control (ATC) for an instrument landing system (ILS) approach.
An ATSB investigation report details that the Corporate Air operated aircraft, with two pilots and 10 passengers on board, was conducting a charter flight from Cobar on the afternoon of 2 July 2024.
“Shortly after commencing the ILS approach, the crew reported that the aircraft became visual with the water and clear of cloud,” ATSB Director Transport Safety Stuart Macleod said.
“However, no request was made to ATC to transition to a visual approach, and shortly afterwards, the pilot flying descended the aircraft below the ILS glideslope.”
As this occurred, the approach controller observed an ATC minimum safe altitude warning due to the aircraft’s descent rate. They assessed the aircraft was above the minimum altitude on the radar terrain clearance chart, and not in unsafe proximity to terrain, and so did not issue a safety alert.
However, this information was passed on to the aerodrome controller, who advised the flight crew they were below the glideslope.
Approximately 3 NM from the runway the rate of descent reduced and the aircraft passed back above the glideslope, before descent increased again and the glideslope was re-intercepted, 1 NM from the runway, at 500 ft.
The aircraft then followed a stabilised flight path to landing.
“Although the crew had briefed and were cleared to fly the ILS approach, the pilot flying descended the aircraft significantly below the 3° glideslope,” Mr Macleod said.
The pilot monitoring reported they stopped monitoring the glideslope after the aircraft became visual.
“The change to a visual approach required a clearance from ATC which was not obtained, and the operator also required a brief to be conducted prior to the commencement of a visual approach, which neither crew reported having occurred.”
Mr Macleod noted that this incident highlights how effective monitoring in a multi-crew environment is paramount to aircraft safety.
“Bringing deviations to the attention of the pilot flying, whether in instrument or visual meteorological conditions, ensures the aircraft remains on a safe flight path and receiving confirmation from the pilot flying can assist in early detection of incapacitation,” he said.
“When an approach has been briefed, flight crew share the same mental model of the expected flight path and deviations can be readily identified, advised and corrected.
“If the approach type changes without further briefing, both crew members are unlikely to have the same expectations, making it difficult for the pilot monitoring to identify and advise the pilot flying of deviations.”
The ATSB’s investigation also determined there were areas of inconsistency within the operator’s standard operating procedures (SOPs) relating to approach procedures in visual conditions.
Additionally, the investigation determined the section of the Aeronautical Information Package (AIP) regarding flight tolerances when conducting a precision approach was unclear as to whether the tolerances were a requirement or a recommendation.
“Corporate Air has since made a number of changes to its SOPs including to its instrument approach procedure,” Mr Macleod noted.
“In addition, CASA has advised it will be amending the AIP to include clearer links to existing legislative requirements, and the use of defined terms.”
Read the final report: Descent below glideslope involving Fairchild SA227, VH-VEU, about 17 km north-east of Brisbane Airport, Queensland on 2 July 2024