Lessons Learned: Freighter Descends Below Glideslope

Glideslope signal interference contributed to a Boeing 767’s descent below glideslope during an approach to Sydney Kingsford Smith Airport.

A descent below glidescope involving Boeing 767, VH-XQU, occurred near the Sydney airport, New South Wales, Australia, on September 10, 2025.

That afternoon, the Tasman Cargo Airlines Boeing 767‑300F with three flight crew on board (including a relief pilot in the jump seat) was conducting a practice autoland instrument landing system (ILS) approach to the Sydney airport at the end of a flight from Hong Kong International Airport.

While intercepting the glideslope for the ILS approach to runway 16R, the 767’s autopilot pitched the nose down, and the aircraft began to descend at a high rate below and away from the glideslope.

The descent triggered an air traffic control minimum safe altitude warning (MSAW) before the autopilot was disconnected and the aircraft leveled out at 1,700 ft, approximately 1,000 ft below the glideslope. It then descended a further 150 ft before a missed approach was commenced. On the subsequent approach, the crew elected to conduct a localizer approach and the aircraft landed without further incident.

What the ATSB found

The ATSB found that 2 Airbus A380s on the ground at Sydney Airport taxied through the ILS critical area and in front of the glideslope antenna, causing interference to the glideslope signal. As a result, after detecting the interference, the Boeing 767’s autopilot established the aircraft on a flight path that deviated away from the glideslope, before alerting the crew that it was operating in a degraded mode.

It was also determined that the pilot flying continued the approach with the autopilot in a degraded mode. As a result, the aircraft’s high descent rate triggered an air traffic control minimum safe altitude warning. After disconnecting the autopilot, the pilot flying delayed the initiation of a missed approach and the aircraft descended below the localizer segment minimum safe altitude. In addition, the pilot monitoring did not effectively monitor the aircraft’s flight path during the approach and did not call out deviations or advise the pilot flying to conduct a missed approach.

Furthermore, it was found that Tasman Cargo Airlines allowed the practice of flight crew exchanging flying and monitoring roles prior to 1,500 ft when conducting a practice autoland. It was also identified that Tasman Cargo’s training did not inform flight crew of the conditions under which ILS critical areas were protected. Consequently, the flight crew believed that the critical area was being protected, and the risk of glideslope interference had been mitigated.

What has been done as a result

Tasman Cargo Airlines has conducted the following proactive safety action:

• Removed the “glideslope out” procedure from its policy and procedures manual (PPM), replacing it with the requirement to conduct a missed approach and notify air traffic control.
• Added a note in the PPM referencing the flight crew operating manual glideslope interference bulletin.
• Published an operational alert regarding Sydney Airport runway 16R glideslope interference with guidance information.
• Updated computer-based training materials to better highlight the ILS critical area and requirements during normal and low-visibility operations.
• Introduced a requirement for the pilot flying to take control of the aircraft prior to the commencement of the approach when conducting an autoland.

In addition, while not in direct response to this occurrence, Boeing advised it is in the process of updating the flight control software for B767 aircraft. Planned for release in 2027, the update will include the following changes:

• The flight director pitch bar will remain biased out of view if the autopilot is disconnected while in attitude stabilising mode.
• Improved glideslope capture logic to reduce the occurrence of false captures leading to attitude stabilizing mode.
• Limiting the flight path angle while in attitude stabilizing mode to be between 0‍–3.25° of descent.
• Display of NO AUTOLAND after being in attitude stabilizing mode for 15 seconds if the aircraft is still above alert height.
• Automatic autopilot disconnect 10 seconds after the display of NO AUTOLAND if the aircraft is still above 500 ft AGL.

Safety message

Flight crew of Boeing 747-400, 747-8, 757, 767, 777 and 787 aircraft should familiarize themselves with their aircraft’s flight crew operating manual bulletin for ILS signal interference and be prepared to conduct prescribed procedures when encountering cockpit indications and autoflight behavior consistent with the issue.

Automation can reduce pilot workload and enhance flight safety. However, it is critical that flight crew maintain constant awareness of the performance of the autoflight system. When under the control of automation, a flight crew should monitor the flight path and verify that aircraft behavior is consistent with the automation modes and parameters selected. If a discrepancy is identified, automation should be disconnected or the level of automation reduced until control is re-established.

Content/image credit/source: ATSB (Australian Transport Safety Bureau), “Descent below glidescope involving Boeing 767, VH-XQU, near Sydney Airport, New South Wales, on 10 September 2025,” AO-2025-055, final report, published June 10, 2026.