Flight planning tasks

As many activities which involve man machine interaction, Flight Planning involves the collaboration between a user and a system in the retrieval, analysis and computation of data to reach a complex solution. We propose to look at Flight planning as a system of cognitive activity distributed between individuals and technologies. We borrow the distributed cognition notion from Hutchins (1995): « distributed cognition is a new branch of cognitive science which studies the representation of knowledge at the same time in people’s minds and in the world ; the propagation of knowledge between individuals and the artefacts ; and the transformations that these structures go through when they are used by the individuals and the artefacts ».

The novelty of this approach is that the unit of our analysis becomes the system composed of the individuals and the artefacts that they use. Artefacts are cognitive in the sense that they embed socially constructed knowledge, support co-ordination between individuals and shape the mental processing required to interact with them. In this respect, Hutchins (1995) introduces the concept of collaborative manipulation : « the process by which we take advantage of artefacts designed by others, sharing ideas across time and space ».

The preparation of a flight plan for a flight requires the Flight Operations department to select the best route that day, taking into account a number of factors such as the weather, the type of aircraft, the weight of the load, the air restrictions. The notion of best route is variable in the sense that while safety is paramount, the relative balance of economy of fuel and time can vary. Thus the best route can be the shortest route in terms of time one day, and the most economical in fuel consumption another day. The process of selecting a route for a flight is therefore one of combining all the existent constraints to reach a best fit solution. This process is shared between a number of cognitive actors : the navigation experts who decide the possible routes, the aviation administration who fixes the safety limitations for each type of aircraft, the accounting departments who fix the fuel policies, the dispatchers who evaluate the constraints of the specific flight, the computer system which computes the implementation of a route as a specific flight, the pilot who estimates the possibility of actually flying the theoretical flight plan.

The decision process in flight planning cannot be decomposed in a set of independent choices individually derived from the satisfaction of specific conditions. Nor can it be characterised by an initial phase in which the flight dispatchers  define the requirements, gather all the relevant information and then produce a plan which satisfies the prerequisites. The decision process can be best described as one of progressive adjustment of the solution.

FLIGHT PLANNING IN COMMERCIAL AIRLINES

A flight plan is a very detailed description of an intended flight for the benefit both of the pilot and air traffic control (ATC) who will then distribute it to all organisations concerned with the flight. Flight planning is the activity of producing an ATC message compiled by or on behalf of the Pilot in Command to a set Civil Aviation Authority format and then transmitted by the appropriate ATC authority to the organisations concerned with the flight. It is the basis on which ATC clearance is given for the flight to proceed. The flight plan details the route by listing all the waypoints (aviation radio beacons or airfields) that the flight traverses; each waypoint is specified by name, co-ordinates, and radio frequency and the flight plan specifies the flight level (altitude) of the plane at that point, the fuel consumption (overall and from the last waypoint), distance covered and time passed.

Three alternative destination airports, the alternates, must also be specified and other safety issues, such as en route airfields for emergency landings on long range oceanic flights. Furthermore the flight plan provides the exact indication of the amount of fuel that will be used during the flight and therefore serves as an instruction for ground maintenance for refuelling the aircraft.

In commercial airlines flight plans are prepared in the Flight Operations department by dispatchers even though ultimate responsibility for accepting the plan, rests with the pilot. Indeed both the pilot and air traffic control can reject a plan. Safety is always the primary concern, but each airline, route and even flight will have further specific constraints to satisfy: maximising payload, giving priority to fuel consumption, guaranteeing punctuality, avoiding congested airspace, these and others are some of the priorities that will vary case to case. Routes are prepared and stored by Navigation departments who calculate trajectories on the basis of airway constraints, time, overflight charges, and commercial agreements.

All commercial airlines use computer based systems to compute flight plans. In simple terms, the flight plan produced by the computer system provides a proposed best route between origin and destination, and a simulation of the flight in terms of time to fly, profile of the flight and fuel consumption.  These computer systems principally use stored routes, of which there can be tens of thousands stored in the navigation database. Most systems also have a random routing facility that can calculate a route between origins and destinations for which there are no stored routes. The selection of a route has to take into account data on the specific aircraft being used (performance varies for each individual plane), on the payload for the flight, the air traffic situation, conditions in all relevant airports and of course, meteorological data.

Furthermore a number of factors affect the amount of fuel to be loaded on a plane: the greater the payload the greater the fuel consumption, carrying a lot of fuel also increases the weight, prices of fuel may vary significantly between origin and destination, there may be weight restrictions for landing at an airport, winds and temperature affect fuel consumption and thus so does altitude, changing altitude is fuel costly, holding (waiting for clearance to land) consumes fuel, the aircraft must have enough fuel to reach all the alternates, etc.

PREPARING A FLIGHT PLAN

The actual task of preparing a flight plan is a joint activity of flight dispatchers and flight planning system with the additional contribution of meteorological, navigational, reservation departments and civil aviation authorities. Although there are individual differences in strategies in different airlines because of different flight planning systems and department organisations, there is a relatively common set of steps that are followed. This very simplified version of the task sequence, results from observations carried out in eight commercial airlines in Europe, Africa and the Middle East over the period of a year.

The dispatchers opens a flight request file on the Flight Plan System on which the parameters of the flight will be inputted prior to the sending off of the request to the computer system for the calculations,   The dispatchers checks the aircraft type, estimated time of departure, origin and destination and enters them in the system. Each individual aircraft has a specific performance envelop, furthermore engine types, aircraft model etc. might be relevant not just in terms of the performance of the aeroplane but also with respect to external constraints like regulations on long haul flights, acceptable runway lengths etc.   The dispatcher decides the en route and destination alternates and enters them on the system,   The dispatcher checks the surface weather of the alternates. The Surface Weather is a report of the local weather conditions dispatched regularly by each airport : it contains data like the visibility, temperature, cloud configuration, winds, rain, snow etc. all the factors that might affect the landing of aircraft,   The dispatcher checks the NOTAMs for the destination and alternates and for en-route. NOTAMs (NOTices to AirmeN) detail all the activity that might affect aircraft : ranging from military exclusion zones, military exercises, rocket launches, balloon flights, to the icing condition of airport landing strips, new radar systems in a control tower,   ·       The dispatcher modifies the alternates if there is a problem with the weather forecast or NOTAM,   The dispatcher enters on the system any particular restriction that this flight may need (fuel, route, aircraft),   The dispatcher enters an estimated payload in the system. Payload information clearly affects the computation of a flight plan. This data will come from the reservation and cargo departments, and might not be accurate until the last minute,

A first Flight Plan computation is run,   The system computes a flight plan with the route, the expected time length of the flight, the expected fuel consumption of the flight, the flight profile, etc.   The dispatcher checks the result of the Flight Plan computation : time, route, fuel, flight profile,    If any characteristic of the flight is found to be inadequate or unsatisfactory the dispatcher modifies a parameter (e.g. a flight level, an additional amount of fuel),      The dispatcher checks the route against significant weather. The Significant Weather (or Meteo) is an interpreted summary of the weather conditions at present and forecasted, that generally covers a significantly wide area (country, continent). It is compiled by  meteorological offices. Upper winds and temperatures are available to the computer as well and affect the computation.

If necessary the dispatcher modifies the route or a leg of the route by entering on the system a preferred route or by blocking a leg of the route as compulsory,   The dispatcher requests a new Flight Plan computation,   The system computes another flight plan for the specific route which has been requested,   The dispatcher compares the new flight plan to the first one and goes through some of the verifications again.

If the solution is still not fully acceptable the process is repeated   If it is acceptable the flight plan is finalised, presented to the pilot and filed to ATC for acceptance. Some airlines are starting to have some access to ATC traffic information e.g. EUROCONTROL’s Central Flow Management Unit. The most striking characteristic of the flight planning activity described above, lies in the interplay between the dispatchers and the flight planning system as a process of progressive adjustment of the solution.

The joint human-machine system works as a whole distributing cognitive and computational tasks between the parties. Dispatchers compute a few plans, progressively adding information as they obtain it but also modifying parameters on the basis of their evaluation of the plan produced.  Dispatchers need to have a computed plan to evaluate because the complexity of the parameters does not allow them to predict how the implementation of a route within the constraints of weather, time, and aircraft will be realised.

From the perspective of the dispatcher, there are two types of decisions to be taken : what are the acceptable parameters for the flight and whether the produced flight plan is good. First dispatchers enter data in the system to describe the minimum characteristics of the flight, origin destination, time of departure, payload, alternates on the basis of the information obtained from other departments and various information systems. Then a plan is computed, which provides a route, a time, a fuel consumption. At this point the dispatcher must judge the plan on the basis of different criteria such as safety and economy. If the plan is not considered acceptable or if the dispatcher wants to test another alternative, the dispatcher makes an hypothesis on what factors could modify positively the plan, inputs a new set of values for some parameters and re-computes.   The two types of decisions are not independent. The amount of fuel depends on the route flown but the choice of route can be constrained by reducing the fuel burn. Therefore decisions cannot be taken individually based solely on the satisfaction of prerequisite conditions.

Although, there are a number of prerequisite conditions to evaluate before selecting the values of the parameters, (e.g.  the surface weather and NOTAMs for the alternates, the overall weight of the aircraft for takeoff and landing) ; satisfying the preconditions is not sufficient to select the final parameters. Firstly because there may be a number of elements that satisfy the conditions, secondly because the decisions are based on combinations of multiple factors which are interdependent.

If we take the case of the route, the minimum conditions to satisfy, are the absence of any traffic or safety restrictions on the route, acceptable weather conditions, and for some type of aircraft, the possibility of having en route landing grounds. However once these conditions are found to be satisfied, the selection of the route is then based on another set of criteria such as route length, possibility of flying at a certain altitude, overflight charges, time, airline policies. Furthermore, not all of the information is available up-front (weather forecasts are updated every six hours therefore it is best to wait for the most recent update), which implies that dispatchers must work with an incomplete knowledge basis and progressively refine the plan to include all of the affecting factors as they appear.

The number, complexity and uncertainty of the factors means therefore, that it is virtually impossible for the dispatchers to predict the outcome of the computation of the plan. Dispatchers systematically compute a first tentative flight plan to use as the basis for further adjustments. In this first calculation just the parameters that are necessary to produce a realistic plan (aircraft type, destination and maybe a set of flight profiles) are entered, while uncertain parameters like the payload, are inputted with estimated values. The flight plan produced by the Flight Planning system relates the route to the flight time and the current meteo.

Any route information retrieved in the Navigation files or charts is static and not useful for evaluating the adequacy of a route for a specific flight because the routes are not put in relation with the actual meteo, and no information is given regarding the time needed to fly that route.  Therefore the flight plan produced by the system gives the dispatchers information that they could not obtain by the different sources individually.  The produced flight plan  has then to be evaluated by the dispatcher to check whether it is the best plan given the constraints of the aircraft, the constraints in terms of possible routes, the weather conditions, and eventually adjusted to meet the constraints.

DISCUSSION

The work in a Flight Operations departments is highly collaborative (Layton, Smith & McCoy 1994), there are a number of actors involved in a flight plan : the navigation department which prepares the possible routes, the reservation department which provides the information about payload, the meteo department which provides the significant weather, and the dispatch department who prepares the flight plan. Dispatchers have the responsibility of collecting the relevant information from the different sources, entering the relevant parameters in a system that computes the flight plan, evaluating the adequacy of the result and adjusting the parameters according to the output.  Since the complexity of calculation of a flight plan is enormous, the task of generating a flight plan is distributed across departments, computer systems, and pre-computed social supports such as routes and policies.  Within this system, the dispatchers play a pivotal role that correspond to what Hutchins (1995) describes as : « providing the internal structures that are required to get the external structures in co-ordination with each other ».

REFERENCES

Hutchins, E. (1995). Cognition in the wild. MIT Press : Cambridge Massachusetts.

Layton, C., Smith, P.J., and McCoy, E.C. (1994). Design of a co-operative problem-solving system for en-route flight planning : an empirical evaluation. Human Factors 36, (1), 94-119.

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