Explanatory Statement
Civil Aviation Regulations 1988
Instructions — use of RNAV (GNSS) approaches by RNP-capable aircraft
Legislation
Section 98 of the Civil Aviation Act 1988 (the Act) provides that the Governor-General may make regulations for the Act and in relation to the safety of air navigation.
Under subregulation 179A (1) of the Civil Aviation Regulations 1988 (CAR 1988), CASA may issue instructions in relation to Instrument Flight Rules (I.F.R.) flights specifying the method by which an aircraft is to be navigated and how a positive position fix is to be obtained.
Instrument CASA 608/08, issued under subregulation 179A (1) of CAR 1988, provides instructions as to how a pilot in command of an aircraft operating under the I.F.R. may use the Global Positioning System (GPS). Among other things, the instrument details the procedures for using GPS for carrying out non‑precision approaches, now referred to as RNAV (GNSS) procedures. It specifies the navigational equipment that must be installed.
ICAO rule changes
It is Australian aviation policy that instrument flight procedures should conform to the International Civil Aviation Organization (ICAO) design rules (ICAO Document 8168, commonly referred to as PANS‑OPS). Approximately 450 RNAV (GNSS) approaches designed in accordance with PANS‑OPS have been commissioned at 260 aerodromes across Australia. Those procedures are designed to be flown by aircraft equipped with self-contained GPS receivers and operated in accordance with Instrument CASA 608/08.
However, most modern Australian turbo‑jet airline aircraft are equipped with computerised flight management systems (FMS) that are more sophisticated than the GNSS navigation equipment mentioned in CASA 608/08. Such aircraft use GNSS positioning to update multiple inertial reference systems (IRS) employing self‑contained laser guided gyroscopes. These navigation systems are designed to comply with Required Navigation Performance (RNP) standards, and the operating procedures and cockpit displays are related to the RNP capability of the aircraft rather than to a specific GNSS receiver used by other less sophisticated aircraft.
On 25 November 2004, ICAO amended the criteria for RNP approach procedure design to reduce the obstacle clearance widths for RNP procedures. For aircraft capable of RNP 0.30, the new ICAO criteria require a lesser obstacle clearance area than is the case for aircraft using the “basic” GNSS receivers on which current RNAV (GNSS) approach procedures are based. Consequently, all existing RNAV (GNSS) approach procedures can now be flown by RNP 0.30-capable aircraft.
Although equipped with more sophisticated navigation systems, modern airline aircraft are not directly compatible with the relatively simple Australian airworthiness requirements that apply to the use of GNSS by general aviation aircraft. Consequently, special evaluation of each aircraft type has been necessary to approve FMS-equipped airline aircraft with GNSS updating capability to conduct RNAV (GNSS) approach procedures. Approvals have been given to Jetstar Airways Pty Limited (Jetstar) and Qantas Airways Limited (Qantas) on this basis, but the process of evaluation and approval is complex and resource intensive.
With the change to the ICAO design rules, it is now possible to approve FMS-equipped aircraft to conduct RNAV (GNSS) approach procedures on the basis of their RNP capability without the need for individual type approval. Skytraders Pty Ltd (Skytraders) has applied for such approval for the Airbus A319 aircraft.
The instrument, therefore, contains procedures to allow for the conduct of RNAV (GNSS) approaches by Skytraders in Airbus A319 aircraft capable of RNP 0.30 performance (the specified aircraft). The RNP capability of an aircraft is specified in the aircraft’s flight manual (AFM) and displayed to the flight crew by the FMS.
RNAV (GNSS) approach procedures provide improvements in safety by allowing runway‑aligned straight-in approaches, the use of automated flight systems, and vertical navigation. The instrument allows the specified aircraft to use existing RNAV approach procedures, thereby providing straight-in approach capability at almost every runway in Australia. This offers a significant safety benefit to those operations.
Conditions and procedures
The instrument sets out the conditions to be satisfied by Skytraders and its specified aircraft for the approval to apply, and the procedures to be followed, during an RNAV (GNSS) approach.
For example, the AFM must expressly state that the aircraft is capable of meeting the requirements of RNP 0.30. RNAV must not be used to satisfy the requirements of alternate aerodrome planning, or used as a navigation reference for certain flights. The aircraft must be operated in accordance with the manufacturer’s instructions. Although not required to be expressly stated, as a matter of law, the flight crew must also comply with the relevant instrument rating requirements under Civil Aviation Order 40.2.1, and with the approved tests and checks under the training and checking organisation requirements in regulation 217 of CAR 1988.
The flight crew may not use a vertical navigation path (VNAV path) for any planned approach unless the operator has established that the path is suitable for the aircraft. Suitable means that the vertical path described by the FMS is at, or above, the path identified in the published approach chart, and that the flight crew do not have to intervene by selecting an alternative mode of flight to the VNAV path. However, the flight crew may alter speed provided this does not affect the VNAV path. Despite the assessment of a VNAV path as suitable, the flight crew must also observe any vertical limitations on approach paths.
Under the procedures, the flight crew are required to ensure that the particular RNAV (GNSS) approach is loaded in the FMS from the current approved navigation database (and consistent with paragraph 9A.3 of Civil Aviation Order 20.18 loaded in such a way that it cannot be modified by the operator or flight crew). The flight crew must ensure that the RNP 0.30 value is displayed and selected. The pilot in command must use the method of control (autopilot or flight director) that, in accordance with the AFM, permits RNP 0.30 operations to be conducted. Cross-track errors (cross-track differences between indicated position and planned position of the aircraft) must be closely monitored by at least 1 pilot. This would enable immediate corrective action, if necessary. The RNAV (GNSS) approach may only be flown using the current approved navigation database that sets out the relevant approach. The RNAV (GNSS) approach must be discontinued if navigation of the aircraft exceeds, or cannot meet, the manufacturer’s stated limits for the RNP 0.30 capability.
For an approach, the selected vertical flight path must be engaged before the aircraft reaches the final approach waypoint.
Legislative Instruments Act
Subregulation 179A (3A) of CAR 1988 declares instructions to be a disallowable instrument. Under subparagraph 6 (d) (i) of the Legislative Instruments Act 2003 (the LIA), an instrument is a legislative instrument for section 5 of the LIA if it is declared to be a disallowable instrument in legislation in force before the commencement of the LIA. The instructions are, therefore, a legislative instrument and are subject to tabling and disallowance in the Parliament under sections 38 and 42 of the LIA.
Consultation
Consultation under section 17 of the LIA has not been undertaken in this case. The instrument renews a previous instrument CASA 23/08 which ceases to have effect on 19 December 2008. Jetstar and Qantas have been issued with similar instruments.
The instrument commences on 20 December 2008 and stops having effect at the end of November 2010.
The instrument has been made by a delegate of CASA, under subregulation 7 (1) of CAR 1988.
[Instrument number CASA 648/08]