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

CHAPTER II. IMPLEMENTATION OF PMS FOR TASHKENT TMA.
2.1 Expected benefits.
Point Merge inherits from general P-RNAV improvements, and is also expected to bring the following specific benefits:
Maintain current runway throughput, during longer periods and with high accuracy (i.e. making full use of available runway capacity at main airports during peak periods) with the potential to match future runway capacity increases;
Maintain, or possibly increase terminal airspace capacity (through a reduction in controller’s workload and in radio-telephony channel occupancy);
Improve flight efficiency and predictability (through extensive RNAV application and use of FMS lateral guidance even in high traffic);
Minimise the environmental impact – or optimise it in respect of defined target levels (by enabling more systematic implementation of continuous descents and containing 2D footprint);
Address staffing and qualification (with standardised and streamlined controller working methods);
Improve safety (through all of the above).
Point Merge is actually expected to enable a trade-off between these individual improvements, accounting for local constraints.
Point Merge aims at optimising the use of airspace for the integration of flows in busy traffic situations, in terms of capacity, predictability and environmental aspects, but also where possible in terms of track miles flown. All other things being equal, it is indeed not expected that Point Merge would result in longer distances or larger time flown than with current procedures.
2.2 Anticipated constraints.
Anticipated constraints include those resulting from the use of RNAV in terminal airspace, and those that are specific to Point Merge.
From an ATC perspective, P-RNAV related issues in terminal airspace include for instance:
- change management – as for any new technology.
- need to include ATC service providers and all involved stakeholders, from an early stage, in the design process.
- navigation accuracy-related constraints: database consistency (including content, interpretation, coding), accuracy of input sources to the RNAV system, and RNAV systems standardisation issues;
- information on (and display on CWP of) aircraft capability;
- radio procedures (including R/T provisions at ICAO level and designation of RNAV routes) to cover RNAV application in terminal airspace;
- potential confusion over responsibility for terrain clearance;
- adequate training to handle specific RNAV aspects (e.g. heterogeneous RNAV-flown turns).
In addition, the following constraints could specifically result from the implementation of Point Merge:

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  path stretching capability and maintenance of “runway pressure” not simultaneously maximized (including capability to easily fill gaps in the sequence due to e.g. go-around, late direct-to).
  
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  applicability to various terminal airspace types due to triangle-shaped route structure – taking into account local constraints (e.g. TMA size, environment, TSAs, complexity of arrival/departure flows);
  
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  continuous reliance on vertical separation for a certain duration (parallel sequencing legs) with potentially more severe consequences in case of failure.
  
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  need for efficient traffic metering at the Point Merge system’s entry in order to avoid too frequent sequencing legs run-off (or use of holding stacks);
  
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  possible sensitivity to perturbations (e.g. wind) or aircraft performance according to design options;
  
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  FMS or ground FDPS route used for computations vs. actual route flown; resulting potential errors in estimates, and impact on fuel management;
  
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  need for specific recovery procedures, specific constraint of compatibility with Point Merge route structure.
  

The main related KPAs are here operability and safety. P-RNAV human factors in terminal airspace include:
Acceptability issues for air traffic controllers related to change in operating method:

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  method being less demanding and repetitive, risk of controllers becoming bored or having less job satisfaction and/or being less vigilant (the risk of a reduction in vigilance may need to be addressed through e.g. safety awareness campaigns and recurrent training).
  
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  risk of controllers’ de-skilling with regards to open-loop vectoring (simulation recurrent training might, in future, be required to keep controllers’ skills up to the level required to cope with anomalies, i.e. unexpected/non-nominal situations).
  

Feasibility issues for air traffic controllers:
- handling of mixed equipage and of non-nominal or abnormal situations;
Acceptability issues for flight crews:
- related to change in working methods.
In addition, the following human factors could specifically need to be considered with Point Merge:
Acceptability issues for air traffic controllers related to change in operating method:

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  change in roles and task allocation between controllers;
  
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  procedure more flexible than existing P-RNAV procedures (involving a fixed route or route changes with defined waypoints), but less than open-loop vectoring with potentially more frequent switch to alternate procedures (e.g. radar vectors);
  
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  unusual merging on a point (rather than an axis) for terminal airspace;
  
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  with more time spent proportionally in P-RNAV (than e.g. trombone procedures), impact of global reversion to vectors (even though it should be a rare event);
  
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  perception of larger airspace required, and longer distance flown, than with current procedures – due to published procedure involving the longest route.
  

Feasibility issues for air traffic controllers:

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  impact on controllers’ team work and co-ordination;
  
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  differential effect of strong winds due to PMS geometry.
  

Acceptability issues for flight crews:

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  unusual situation, flying on a sequencing leg with vertical separation from opposite traffic on parallel leg;
  
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  subjective implication of a published procedure involving a long route (however this is similar to some existing P-RNAV procedures such as e.g. trombone routes).