ATSB finds glideslope interference behind B767F incident

By Andrew Curran.

The Australian Transport Safety Bureau (ATSB) has released its final report into an incident involving a Tasman Cargo Airlines B767-300F that descended below the glideslope while approaching Sydney Airport (SYD) on September 10, 2025.

The report, issued on July 9, found that glideslope signal interference contributed to the incident, which occurred during a practice autoland instrument landing system (ILS) approach. The aircraft involved was VH-XQU (msn 37806), an almost 17-year-old freighter operated by Tasman Cargo Airlines on behalf of DHL.

On board were three flight crew - the captain, who occupied the left seat as pilot monitoring, the first officer, who occupied the right seat as pilot flying, and a relief pilot occupying the jump seat. They had flown down from Hong Kong (HKG).

Freighter 2,200 feet at 19 kilometres out from the airport and still descending

According to the ATSB, while intercepting the glideslope for the ILS approach to runway 16R, the aircraft’s autopilot pitched the nose down and the aircraft began descending below the glideslope. Shortly afterwards, the crew received an autopilot caution and associated alerts.

The freighter continued descending below the glideslope, maintaining an average descent rate of 1,650 feet per minute for approximately 60 seconds. During this time, the crew discussed abandoning the ILS approach in favour of a localiser approach.

When the aircraft was about 19 kilometres from Sydney Airport, air traffic control radar recorded it at 2,200 feet and descending at 1,731 feet per minute, triggering a minimum safe altitude warning.

Before being alerted by air traffic control, the crew disconnected the autopilot and levelled the aircraft at 1,700 feet, approximately 1,000 feet below the glideslope. The aircraft then descended a further 150 feet before the crew initiated a missed approach after receiving a low altitude alert from the approach controller.

A380s interfere with the glideslope signal

The ATSB found that, during the B767's approach, two A380s taxied into the instrument landing system critical area, located in front of the glideslope antenna and including the A1 holding point for runway 16R.

“The 767 crew believed that their advice to ATC of their intent to conduct a practice autoland, as well as the weather conditions, meant ATC would prevent aircraft entering the ILS critical area, but this was not the case,” said ATSB Director of Transport Safety Stuart Macleod.

The investigation also found the tower controller was required to advise the Tasman Cargo crew that the ILS critical area was not being protected. However, the flight had not yet been transferred to the tower frequency, so that advice was never passed on.

“When the A380s taxied through the ILS critical area, interfering with the glideslope signal, the B767’s autopilot established it on a flight path that deviated away from the glideslope,” Macleod said.

“The autopilot then notified the B767 crew that it was operating in a degraded mode, but the pilot flying continued the approach.”

ATSB findings and Tasman Cargo Airlines’ response

The investigation found the pilot monitoring did not effectively monitor the aircraft’s flight path and did not call out deviations or direct the pilot flying to conduct a missed approach.

The ATSB also found Tasman Cargo Airlines permitted flight crews to exchange flying and monitoring duties before 1,500 feet during practice autoland approaches.

It further found the airline’s training did not explain the conditions under which ILS critical areas are protected. As a result, the crew incorrectly believed the critical area was protected and that the risk of glideslope interference had been mitigated.

In response, Tasman Cargo Airlines has taken a series of proactive safety actions, including:

• Removing the 'glideslope out' procedure from its policy and procedures manual and replacing it with a requirement to conduct a missed approach and notify air traffic control.
• Adding a reference to the flight crew operating manual's glideslope interference bulletin.
• Publishing an operational alert covering glideslope interference on Sydney Airport's runway 16R.
• Updating computer-based training to better explain ILS critical area protection during normal and low-visibility operations.
• Requiring the pilot flying to take control of the aircraft before commencing a practice autoland approach.

Boeing to provide B767 software update

Separately, Boeing advised the ATSB it is developing a flight control software update for the B767, scheduled for release in 2027. The update will:

• Keep the flight director pitch bar out of view if the autopilot is disconnected while in attitude stabilising mode. 
• Improve glideslope capture logic to reduce false captures leading to attitude stabilising mode. Limit the flight path angle in attitude stabilising mode to between 0° and 3.25° of descent. 
• Display a NO AUTOLAND message after 15 seconds in attitude stabilising mode if the aircraft remains above alert height.
• Automatically disconnect the autopilot 10 seconds after displaying NO AUTOLAND if the aircraft remains above 500 feet above ground level. 

Macleod said the incident was a reminder that automation, while designed to reduce pilot workload and enhance flight safety, still depends on flight crews actively monitoring aircraft performance.

“Flight crews should constantly monitor and verify that aircraft behaviour is consistent with the automation modes and parameters selected,” he said.

“And when a discrepancy is identified, automation should be disconnected, or the level of automation reduced, until control is adequately re-established.”

You can read the full final report here.

Photo: Tasman Cargo Airlines.

Contact the writer: andrew@aerosouthpacific.com