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.
ICAO rule changes
It is Australian aviation policy that instrument flight procedures should conform to the International Civil Aviation Organisation (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.
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. 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 without further analysis or design of the instrument approach procedure.
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 (e.g. B737NG) to conduct RNAV (GNSS) approach procedures. Approvals have been given to Qantas Airways Limited (Qantas) and Virgin Blue Airlines Pty Limited 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. Qantas has applied for such approval.
The instrument, therefore, contains procedures to allow for the conduct of RNAV (GNSS) approaches by Qantas in Boeing 737-800 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 RNP 0.30‑capable 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 Qantas 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 method of control to that described by the FMS. 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 dedicated to the task to 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.
The instrument replaces Instrument CASA 189/05, which expires at the end of July 2008, and replaces it with revised instructions for Qantas Boeing 737-800 aircraft which have the requisite RNP capability.
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 has been requested by Qantas and has been issued because its aircraft are capable of meeting the RNAV (GNSS) RNP 0.30 requirements. In accordance with the ICAO standard, a similar instrument would be issued to any operator whose relevant aircraft can meet these exacting standards of navigation performance and are expressly endorsed as such by their manufacturer.
The instrument commences on 1 August 2008 and stops having effect at the end of 31 July 2010.
The instrument has been made by a delegate of CASA under subregulation 7 (1) of CAR 1988.
[Instrument number CASA 398/08]