ATSB urges fitment of terrain avoidance and warning systems to smaller passenger aircraft

  • Aircraft was being flown 1,000 ft below the recommended descent profile, and had probably entered areas of significantly reduced visibility, including heavy rain;
  • The pilot was probably experiencing a very high workload, and it is evident they did not effectively monitor the aircraft’s altitude and descent rate for an extended period;
  • A TAWS (terrain avoidance and alerting system) would have provided the pilot with both visual and aural alerts of the approaching terrain for an extended period.

A Cessna 404 with a pilot and four passengers on board was being flown 1,000 ft below the recommended descent profile before it collided with sand dunes about 6.4 km (3.5 NM) short of the runway at Lockhart River, an ATSB investigation report details.

The twin piston-engined Cessna was operating a charter flight under the instrument flight rules from Cairns to Lockhart River on the morning of 11 March 2020. Consistent with the weather forecast, at Lockhart River there were areas of cloud and rain that significantly reduced visibility. Recorded data showed that the pilot commenced a go-around while conducting an area navigation (RNAV) GNSS instrument approach, using the aircraft’s instruments and two GPS units, to runway 30.

The pilot then commenced a second approach to land at Lockhart River, during which the aircraft probably entered areas of significantly reduced visibility, including heavy rain.

“The aircraft appeared to have been in controlled flight up until the time of the impact, and there was no evidence of any medical problems or incapacitation for the pilot, nor pre-existing mechanical problems with the aircraft or its systems,” said ATSB Chief Commissioner Angus Mitchell.

The pilot and passengers were fatally injured in the accident, and the aircraft was destroyed.

From the available evidence – the aircraft was not fitted with a cockpit voice recorder or a flight data recorder, but nor was it required to be – the ATSB could not conclusively determine the most likely scenario to explain the descent below the recommended profile on the second approach.

The ATSB considered three main scenarios as to why the aircraft was operated 1,000 ft below the recommended descent profile: that the pilot thought they were one segment further along the approach; that the pilot believed they were 1,000 ft higher than they actually were during most of the descent; and that the pilot intentionally descended below the recommended descent profile and segment minimum safe altitude in order to maximise the chances of becoming visual before reaching the missed approach point.

“Overall, mis-reading the altimeter by 1,000 ft appears to be the most likely scenario, although there was insufficient evidence to provide a definitive conclusion,” Mr Mitchell noted.

“Regardless, it is evident from the continued descent that the pilot did not effectively monitor the aircraft’s altitude and descent rate for an extended period, and that they were probably experiencing a very high workload.”

Mr Mitchell noted that conducting instrument approaches in poor visibility and hand flying an aircraft in single-pilot operations is particularly demanding.

“In addition to the normal high workload associated with a single-pilot hand flying an instrument approach in poor visibility, the pilot’s workload was elevated due to conducting an immediate entry into the second approach, conducting the approach in a different manner to their normal method, the need to correct lateral tracking deviations throughout the approach, and higher than appropriate speeds in the final approach segment.”

The accident aircraft was equipped with two Garmin GNS 430W GPS navigation and radio units, which have an advisory-only terrain awareness function capable of providing visual pop-up terrain alerts. However, it was unclear if the pilot had selected this function during the accident flight. While the operator did not provide procedures or guidance for its pilots on the function’s use, nor was it common for operators of aircraft with such units to do so.

Mr Mitchell said the ATSB’s investigation highlighted the importance of a terrain avoidance and warning system (TAWS) in preventing controlled flight into terrain (CFIT) accidents, and urged operators of smaller aircraft conducting passenger operations to consider their fitment.

“Given the aircraft’s descent profile on the second approach, a TAWS would have provided the pilot with both visual and aural alerts of the approaching terrain for an extended period.”

There was no requirement for the accident aircraft to be fitted with a TAWS. As part of the long-planned introduction of new Civil Aviation Safety Regulations on 2 December 2021 (Parts 121 and 135), the Civil Aviation Safety Authority mandated the fitment of a TAWS to piston-engined aeroplanes used for air transport with a passenger seating capacity of 10 or more. However, even if the changes to the TAWS requirements had been introduced in Australia earlier, they probably would not have resulted in an aircraft such as that used during the accident flight being fitted with a TAWS.

“The ATSB urges all operators conducting air transport operations to evaluate the risk of CFIT in your operations and to actively seek to install TAWS in your aircraft to maximise the safety of your operations,” Mr Mitchell said.

“And if a TAWS is not currently viable, but your aircraft has a GPS/navigation unit that provides a terrain awareness function, fully understand the nature and limitations of this function and develop procedures and guidance for your pilots about its operation.

“Further, seek to fit your aircraft with a GPS/navigation system that provides vertical guidance on non-precision approaches; develop or review flight profiles for instrument approaches; develop or review your stabilised approach criteria to ensure it is suitable for instrument meteorological conditions; and review the content and frequency of your flight crew proficiency checks to ensure they provide sufficient opportunities to monitor the way instrument approaches are being conducted during line operations.”

You can find here the report: AO-2020-017 Controlled flight into terrain involving Cessna 404, VH-OZO, Lockhart River, Queensland, on 11 March 2020

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