Faculty of air transport engineering the department of «air navigation systems»

INTRODUCTION
In aviation, a standard terminal arrival route or standard terminal arrival (STAR) is a published flight procedure followed by aircraft on an instrument flight rules (IFR) flight plan just before reaching a destination airport.
A STAR is an air traffic control (ATC)-coded IFR arrival route established for application to arriving IFR aircraft destined for certain airports. Area navigation (RNAV) STAR/FMSP procedures for arrivals serve the same purpose but are used only by aircraft equipped with flight management systems (FMS) or GPS. The purpose of both is to simplify clearance delivery procedures and facilitate transition between en-route and instrument approach procedures. [1]
Enhancements in ATC and airspace procedures that make best use of the aircraft Flight Management System (FMS) can significantly reduce pilot workload and enhance flight efficiency and this is clearly a good thing. However, it is essential that any consequential safety effects on the flight deck are identified and addressed collaboratively between ATC and aircraft operators. A good example of this need is in the fuel management issues related to RNAV arrival routes that use linear holding procedures such as ‘Point Merge’.
Linear holding can be designed into an RNAV STAR. It allows ATC to delay, sequence, and integrate aircraft arrivals by giving routings along predefined variable legs to specific points, instead of providing radar headings. It can also entirely replace or significantly reduce the need for traditional holding stacks. ‘Point Merge’ is a particular type of linear hold that is already in operational use at some airports. ATC arrival clearance is given for the complete longest linear hold route. As the correct spacing is achieved, the aircraft is instructed to route to the ‘merge point’ from where a single arrival path is resumed.
When in a traditional vertical holding stack, or when being provided with headings from ATC, the aircraft FMS is ‘reactive’ in its fuel calculations, as it does not know how many holds will be own or where the controller will vector the aircraft. But when ATC instruct an aircraft to fly the complete RNAV linear hold, the FMS ‘sees’ this route as a ‘closed loop’ and provides landing fuel predictions based on the assumption that this will be own in its entirety. The FMS of course does not know when ATC will provide an instruction to fly to the merge point. As a result, in advance of a clearance to the merge point, in certain circumstances the FMS would generate a fuel-warning message with consequent flight crew uncertainty in their fuel situation despite carrying appropriate fuel loads. This led to some aircraft operators carrying more fuel than was actually needed, a situation that results in extra fuel burnt to carry the extra load. There was also concern that this situation could lead to fuel emergencies being declared when not necessary.
As part of planning for implementation of RNAV linear holding within the RU Future Airspace Strategy, RU CAA facilitated a working group of controllers and pilots to gain full understanding of the problems and issues identified from linear holding deployment in other states. This focused on fuel planning, FMS operation, and ATC techniques and procedures. The outcome was ATC and pilot understanding and agreement on the varying flight deck and ATC demands and safety risks, a set of consistent flight crew and ATC procedures and processes, and identification of next steps.
Improvements in ATC and airspace procedures that make the best use of the aircraft's Flight Management System (FMS) can significantly reduce the workload of pilots and improve flight efficiency, and this is certainly a good thing. However, it is critical that any subsequent impact on flight deck safety is identified and addressed jointly by ATC and aircraft operators. A good example of this need is the fuel management issues associated with RNAV arrival routes, which use linear retention procedures such as "Point Merge".
The linear holding can be constructed in the form of an RNAV STAR. This allows ATC to delay, streamline, and integrate aircraft arrivals by giving routes along pre-defined variable segments to specific points, instead of providing radar headers. It can also completely replace or significantly reduce the need for traditional holding stacks. "Point merge" is a special type of linear hold that is already used at some airports. ATC arrival clearance is given for the complete longest linear hold route. As soon as the correct distance is reached, the aircraft is instructed to proceed to the "confluence point", from where the only route of arrival resumes.
When the aircraft is in a traditional vertical holding stack, or when it is provided with headers from ATC, the aircraft's FMS is "reactive" in its fuel calculations, as it does not know how many holds it will own or where the controller will direct the aircraft. But when ATC instructs an aircraft to fly a full linear RNAV hold, the FMS "sees" this route as a "closed loop" and gives fuel landing forecasts based on the assumption that it will be entirely its own. The FMS, of course, does not know when the ATC will instruct you to fly to the point of merger. As a result, prior to obtaining a merger permit, in certain circumstances, the FMS will generate a fuel warning message followed by uncertainty for the flight crew in their fuel situation, despite the fact that they are carrying the relevant fuel loads. This resulted in some aircraft operators carrying more fuel than was actually needed, which resulted in additional fuel being burned to carry the extra load. Concern was also expressed that such a situation could lead to fuel emergencies being declared when this was not necessary. [2]