ASIM: Airspace SIMulation
(Last Update: 02/96 EMF)
1. Model Category
Airspace complexity evaluation tool.
2. Summary
ASIM is a tool developed in UK at the Defence Research Agency (DRA) for the Civil Aviation Authority / National Air Traffic Services (CAA/NATS). To date, it has been used to evaluate the complexity of new airspace models (new route structures for example) for the period 2015+. At the current stage of its development, RAMS does not fully replicate Terminal Area operations. Thus, operations under 10,000ft are currently filtered out. ASIM was designed specifically to study the impact of new route structures on the United Kingdom airspace operations.The input to ASIM consists of aircraft characteristics, and the desired route structure. The output mainly consists of a count of the number of close proximities among aircraft and points out which aircraft are involved. It is is used to study overall ATC complexity. ASIM also has limited traffic management capabilities.
Competing models include TAAM, SIMMOD, RAMS.
3. Input requirements
Sectors may be defined under ASIM. Aircraft characteristics need to be entered. Each aircraft is assumed to have a preferred height bound and flight levels are assigned randomly from a distribution which depends upon the aircraft type. Aircraft may climb either according to specified climb schedules or follow ATC rules. The aircraft are simply flown from origin to destination. While flight plans are pre-defined, actual flight times may be modeled by injecting randomness. No specific delays are modeled within ASIM.Traffic is generated probabilistically based on statistical information about the number and frequency of flights accross city pairs. Each city pair has a specific routing link-node structure. In that sense, it is “similar” to SIMMOD.
The input interface has been designed so as to be compatible with most standard databases.
4. Outputs
The main output of ASIM is a detailed report of close encounters between aircraft.
5. Major assumptions
ASIM assumes a given route structure for the airspace. There is no weather model included into ASIM, and no attempt to model controller actions. By adequately introducing random variables in departue times and aircraft altitudes, it is assumed that a representative sample of air traffic is generated.
6. Computational characteristics
ASIM runs on a standard workstation. The current implementation is on a DEC Alpha. ASIM has been programed in MODSIM, a high-level programming language that generates C++ and C routines.
7. Learning effort
It was reported that two people with standard training in ATC can become familiar with ASIM in less than a month. The documentation is reported to be very deficient by the developers themselves
8. Modularity and Flexibility
According to CAA/NATS officials, ASIM is mostly developed for the purposes of the United Kingdom. However, the model and its underlying language are object orientated, and it should be easily adapted to handle other needs.
9. Status
ASIM has been under development for 5 years. Further development appears necessary. According to the developers, ASIM should be considered a research tool. However, they also consider the basic model engine to be fully operational and properly validated. The post processing capabilities have been markedly enhanced over the last six months.
10. Extent of model verification
Unknown.
11. Principal application
ASIM was used within the Model Use and Fast TIme Simulations (MUFTIS) project to evaluate the impact of European Advanced Traffic Flow Management on UK flights. ASIM has also been used in a number of other studies, including the European NOAA work programme.ASIM was also used to investigate new, simpler route structures in the vicinity of London. New route structures included great circles. It was found that great circles would reduce the number of conflicts, but would also increase the number of crossing points and would change the closest point of approach distribution.
12. Availability
This software belongs to CAA/NATS. ASIM can be made available on a case-by-case basis.
13. Information for model evaluation
Interview with Graham Stamp (CAA/NATS) on January 15, 1996, with Rob Whitaker (CAA/DRA) on February 13, 1996, and with Philippe Kerlirzin on January 10, 1996.
14. Summary evaluation
ASIM is an enroute simulation model tailored for the needs of the United Kingdom. Its main purpose is to evaluate the complexity of airspace under current and future route structures, including great circles, by counting the number of close encounters. ASIM is a research tool that may be made available to NASA following formal agreements. It seems easily portable on a standard workstation.
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