Proposed amendment to Part 121 MOS to replace expiring provisions and make minor changes - some relevant to Part 135 - (CD 2522OS)

Policy Aim

The aim of the policy is to provide a replacement to the expiring transitional provision. This will allow aeroplanes with higher specification navigation capabilities to take advantage of that navigation capability by establishing an obstacle assessment area (OAA) that is narrower than otherwise permitted.

Proposed Policy

Replace the transitional CAO 20.7.1B method that expires on 2 December 2025. This replacement will contemporise required navigation performance (RNP)-based engine-out departure procedure (EODP) design criteria for OAA, including specifying splay divergence and minimum splay half-widths. This would also include requirements for EODP design to be performed by accredited designers and would also require operators to hold RNP approval required (AR) departure procedure (DP) approvals with associated conditions.

The proposed amendments would include the following conditions as safety controls:

• underlying competencies of the operator and the designer of the EODP:
  • the operator must hold a Part 91 RNP AR DP approval (i.e. regulation 91.045 approval for the purposes of paragraph 91.660(1)(b) with a prescribed navigation specification of RNP AR DP)
  • the designer must be an instrument flight procedure (IFP) design organisation authorised to design RNP-based instrument departure procedures that holds a CASR Part 173 authorisation (could be an authorised or certified designer) or an equivalent authorisation issued by US FAA, EASA, UK CAA, NZ CAA or TCCA (Transport Canada)
• EODP design requirements must include:
  • flight track designed for use by aeroplanes using PBN-based course guidance
  • consideration of the following matters in relation to flight track:
    • the ability of a pilot to initiate and maintain a desired speed and bank angle in a turn
    • the effect of wind on the take-off flight path
    • the effect of temperature on turns
    • the effect of terrain proximity on TAWS warning

• • width of the start of the obstacle assessment area to be consistent with MOS subsection 9.04(2A) to ensure that 90m or for aeroplanes with wingspan of less than 60m, the resultant distance of half-wingspan + 60m
  • obstacle assessment area splay divergence rate must be not less than 0.0625 x D [6.25%]
  • obstacle assessment area half-width must be not less than the larger of:
    • 1x RNP (of the intended aeroplane’s certified RNP capability in the OEI condition), or
    • 370m (irrespective of aeroplane RNP capability better than RNP 0.1nm [i.e. RNP 0.05])
• operational requirements:
  • where obstacle clearance after take-off for a flight is based on this method, the aeroplane must not take-off if, immediately before commencing the take-off roll, the aircraft actual navigation performance (ANP) is greater than engine out departure procedure design half-width RNP value
  • aeroplane must have operative TAWS Class-A
• consequential and minor amendments to 9.04(3) and (4) include:
  • amending paragraph 9.04(3)(b) distance limit to 370m from 300m. This will remove the existing inconsistency where RNP 0.2nm exceeds the 300m limit (which is actually 0.16nm)

• • amending paragraphs 9.04(3)(b) and 9.04(4)(b) to be included as a conditional element that requires the portion of the flight from the departure end of the runway to the lowest safe altitude for the route must be conducted while maintaining the required navigational accuracy of RNP 0.2nm, or better through the obstacle accountability area - 370m (3b) / 600m (4b).