The Australian requirements for installing a terrain avoidance and warning system (TAWS) were less than those of other comparable countries for some types of small aeroplanes conducting air transport operations, and the requirements were not consistent with International Civil Aviation Organization (ICAO) standards and recommended practices. More specifically, although there was a TAWS requirement in Australia for turbine-engine aeroplanes carrying 10 or more passengers under the instrument flight rules:
The ATSB is satisfied that the December 2021 regulatory requirements for piston-engine aeroplanes (with an MOPSC of 10 or more) to have a TAWS has addressed a key part of this safety issue. The regulatory requirements for turbine-engine aeroplanes with an MOPSC of 6–9 have not been addressed. Given the extent of the recent regulatory reform process, it is also unlikely they will be addressed in the near future.
On 2 December 2021, Civil Aviation Safety Regulation (CASR) Part 121 (Australian air transport operations – larger aeroplanes) and CASR Part 135 (Australian air transport operations – smaller aeroplanes) commenced. Air transport operations included passenger transport operations, regardless of whether they were scheduled or charter operations.
CASR Part 121 (except for Part 121.Z) applied to air transport operations in multi-engine aeroplanes that had a maximum operational passenger seat configuration (MOPSC) of 10 or more or had a maximum take-off weight (MTOW) of more than 8,618 kg. Part 121 operations required 2 pilots for all operations and all operations to be conducted under the instrument flight rules (IFR). It also required fitment of a TAWS A for turbine-engine aeroplanes and TAWS A or B for piston-engine aeroplanes.
CASR Part 121.Z applied to air transport operations in single-engine aeroplanes that had a MOPSC of 10 or more and had a MTOW of less than 8,618 kg. It permitted operations to be conducted under Part 135, but prohibited VFR operations at night and required 2 pilots for IFR operations. It also required fitment of a TAWS A for turbine-engine aeroplanes and TAWS A or B for piston-engine aeroplanes.
CASR Part 135 applied to air transport operations conducted in smaller aeroplanes with a MOPSC of 9 or less and a MTOW of 8,618 kg or less. The Manual of Standards for CASR Part 135 stated a requirement for a TAWS for aeroplanes being used for IFR or night VFR flights and with a MTOW of more than 5,700 kg. The required date of implementation was 2 December 2023.
The Civil Aviation Safety Authority (CASA) issued an exemption instrument (EX137/21) to permit air transport operations in single-pilot aeroplanes with a MOPSC of 10–13 (and an MTOW of no more than 8,618 kg) to be conducted under CASR Part 135 (rather than Part 121) for a defined period of time. However, such aeroplanes were also required to have a TAWS (class A for turbine-engine aeroplanes and class A or B for piston-engine aeroplanes). For new operators, the applicable date was 2 December 2021. For operators that already held an air operator’s certificate applicable to the relevant type of aeroplane, the applicable date was 2 December 2022. In addition, any requirements for a ground proximity warning system that applied under Civil Aviation Order 20.18 immediately before 2 December 2021 had to be complied with.
The exemption instrument stated that it would be repealed on 1 December 2024. From 2 December 2024, all multi-engine aeroplanes conducting air transport operations with a MOPSC of 10–13 would be required to be operated under Part 121 (that is, with 2 pilots, under the IFR and with a TAWS fitted), and all single-engine aeroplanes with a MOPSC of 10–13 would be required to be operated under Part 121.Z (with a TAWS fitted).
CASA advised that the definition of MOPSC referred to the number of passenger seats fitted to an aircraft. An operator could not elect to limit the number of seats of an aircraft with a MOPSC of 10 or more through administrative or operational controls in order to have a MOPSC of 9 or less. Rather, seats would have to be physically removed from the aircraft in order to change the MOPSC to 9 or less.
In effect, these new requirements, as and when applicable, are consistent with the standards outlined in International Civil Aviation Organization (ICAO) Annex 6 Part 1 for turbine-engine and piston-engine aeroplanes conducting passenger transport operations; that is, a TAWS for all aeroplanes authorised to carry 10 or more passengers.
As discussed in the investigation report (Considerations of changes in Australia), when developing CASR Parts 121 and 135, CASA also proposed to introduce a requirement for a TAWS for all aeroplanes (turbine- and piston-engine) conducting air transport operations with a MOPSC of 6–9. Following industry consultation, this option was not adopted.
Changes to the Civil Aviation Act 1988 brought about by the Civil Aviation Amendment Act 2019 meant that CASA was required do the following when developing and promulgating aviation safety standards:
(a) consider the economic and cost impact on individuals, businesses and the community of the standards; and
(b) take into account the differing risks associated with different industry sectors.
CASA advised that small aeroplane charter operations prior to, and after, the commencement of CASR Part 135 are a different industry sector to Part 121 operations. Furthermore:
It follows, that the different risks are addressed more specifically within the context of the industry sectors and also the differences in those sectors that might be able to accept or absorb the increased costs of requiring safety mitigators such as TAWS into their operations.
 The MOPSC for an Australian operator was defined as the maximum passenger seat capacity of the aircraft approved by CASA as part of the approval of the operator’s exposition under CASR Part 119 and specified in the operator’s operations manual.
 That is, aeroplanes certified to be operated by a single pilot in accordance with the type certificate data sheet and whose flight manual provided that the flight crew could consist of a single pilot.