Civil Aviation Safety Authority - Project OS 14/01
Issue
In response to a recent Australian Transport Safety Bureau (ATSB) investigation report into a visual flight rules (VFR) flight conducted in dark night conditions, the Civil Aviation Safety Authority (CASA) advised the ATSB of a number of safety actions being undertaken, including the clarification of the term 'visibility' in dark night conditions and the provision of further guidance on night VFR flight planning.
Dark night conditions
The ATSB report outlines that dark night visual meteorological conditions (VMC) are effectively the same as instrument meteorological conditions (IMC). "The only real difference is that, if there are lights on the ground, they can be seen in VMC. In remote areas where there are no lights or ambient illumination, there is no difference. Pilots cannot see the ground and have no external cues available to assist with their orientation".
Visibility is defined in regulation 2 of the Civil Aviation Regulations 1988 (CAR 1988) as "visibility means the ability, as determined by atmospheric conditions and expressed in units of distance, to see and identify prominent unlighted objects by day and prominent lighted objects by night."
Flight visibility is defined as "the average range of visibility forward from the cockpit of an aircraft in flight". Further, regulation 174 of CAR 1988 requires that flight visibility shall be determined by the pilot in command from the cockpit of the aircraft while in flight; and the pilot in command of an aircraft operating under the VFR is responsible for determining the visibility for the take-off and landing of the aircraft. In determining visibility for the purposes of these regulations, the pilot in command shall take into account the meteorological conditions, sun-glare and any other condition that may limit his or her effective vision through his or her windscreen; this would include dark night conditions.
In the context of dark night conditions being encountered and the lack of any other lighted objects as outlined by the ATSB above, it would be very difficult for the pilot to determine inflight visibility.
Helicopter night visual flight certification issues
There is a significant difference between a helicopter's certification for VMC and IMC operations, which centres on both the static and dynamic longitudinal stability of the helicopter. Unlike most aeroplanes, in VMC a helicopter can be certified with highly unstable static longitudinal stability characteristics provided it can comply with basic requirements for correct control sense of motion criteria.
However in IMC, where there is reduced external visual cues for orientation, the certification standards provide for further longitudinal stability requirements, both statically and dynamically. This is significant as outlined above, the reduced visual cue environment as experienced in dark night conditions effectively constitutes IMC and to operate a rotorcraft in such an environment would require the rotorcraft to be capable of meeting the additional IMC stability requirements.
Objective
The project will review the NVFR requirements in the current rule set and future CASR definitions to ensure it limits the visual environment to that in which a defined external horizon is available for aircraft attitude control. The project will examine the night VMC requirements for both rotorcraft and aeroplanes. However the outcome of the project may limit the change to the night VMC requirements to rotorcraft only in recognition of the difference in certification requirements between the categories. The project will also amend the guidance provided in CAAP 5.13-2 to emphasise the importance of maintaining a discernible external horizon at night particularly in light of the certification basis for NVFR rotorcraft.
Rules affected
CAR 2, 172, 174
CASR 91
Thoughts?