35TH ANNUAL CONFERENCE, Tunis, Tunisia, 15-19 April 1996
WP No. 116
RNP for Approach and Landing
In 1994 the current policy on RNP for approach and landing was adopted. Since then, there have been considerable changes in the plans for replacing ILS with new approach and landing aids. This paper proposes that the policy should be amended in the light of these changes.
When the present policy was adopted, states were preparing to change from ILS to MLS as the principle landing aid in accordance with the ICAO ILS/MLS Transition Plan. This would have resulted in a change from one single approach aid (ILS) to another single aid (MLS). It was also anticipated that this world-wide transition would be made in a short period of time (less than 5 years).
Since then, there have been many new developments in the field of approach and landing aids, particularly the possibility that GNSS based systems could be used for precision approaches. As a result of these changes, ICAO held the Special Communications/Operations (COM/OPS) Meeting in 1995 to review the ILS/MLS Transition Plan.
The outcome of the COM/OPS meeting is that the original ILS/MLS Transition Plan has been replaced with new regional transition arrangements. This will see a gradual transition to new aids, probably covering the period 1998 to 2015. In addition, there is no removal date for ILS, and this aid may remain in service for some considerable time. The transition arrangements also recognise that there will be several approach aids in use during this period. As a minimum there will be ILS, MLS and GNSS. There may also be variations on certain systems, e.g. GNSS used with various types of augmentation.
The first sentence of the IFATCA policy seeks to exclude ILS from RNP. There are potential benefits from the introduction of RNP even with ILS still in use. It may simplify the approach scenario and reduce RTF loading. The principle reason for excluding ILS was that the improvements in runway capacity available with new aids will not be available while ILS ground safeguarding is still required. Considering that ILS will continue to be used for a long time, it seems short sighted to loose the potential benefits of RNP until ILS is removed, so it is proposed that the reference to ILS be removed from this sentence.
The second section of the policy states IFATCA’s desire for as short a transition period as possible. ICAO has now determined that there will not be a specific transition period. This does not , however, negate IFATCA’s concern that a long period of time with both ILS and new approach aids in use is undesirable. This may increase ATC workload and it may not be possible to realise some of the benefits of the new aids, such as the increase in runway utilisation in low visibility operations.
In order to bring the policy into line with the transition arrangements adopted by ICAO, yet to still retain our concern, it is proposed to alter policy to state that it will not be possible to obtain the full benefits of RNP unless the ILS is withdrawn.
Due to the changes in the ICAO plans for the transition from ILS to new approach and landing aids, IFATCA policy on RNP needs to be reviewed. It is now clear that ILS will continue to be in use for a considerable period of time. There are benefits from the introduction of RNP during this time, and the continued use of ILS should be amended to reflect this concern.
It is recommended that:
The RNP concept should be extended to cover the approach and landing phases of flight.
RNP standards should be developed in parallel with new approach aids such as MLS and GNSS and should , ideally , be introduced at the same time as these new aids. After the introduction of a new aid, the full benefits of RNP may not be achieved while the ILS is still in use, so the ILS should be withdrawn as soon as practical.
A significant factor in the determination of RNP procedures should be the aim of limiting the increase in ATC workload due to the proliferation in landing aids expected in the future.
Last Update: September 28, 2020