Definition of an aircraft intent description language for air traffic management applications (2008)

To accommodate the expected growth of the air transport industry, the Air Traffic Management (ATM) system is required to increase its performance in terms of capacity, efficiency and security whilst maintaining adequate levels of safety and reducing the environmental impact of aircraft operations. In addition, there is a urgent need to allow
the different actors in the ATM system the flexibility to accommodate their preferences,so that they can better pursue their respective business objectives. To deal effectively
with all these challenges, the current trend is to increase the levels of automation and integration in the system. Different ATM modernisation initiatives pursuit the shift towards a Trajectory Base Operations (TBO) environment, where different ATM users (e.g.,, Air Navigation Service Providers (ANSP), Airlines Operations Center (AOC), pi-
lots, controllers, airport authorities) will exchange trajectory-related information in order to collaboratively make decisions in an e±ficient and fair way.
An increasing number of Decision Support Tools (DSTs) are being developed and implemented to enhance both airborne and ground-based automation systems to support the
human in TBO. Since these DSTs have to help humans to make decisions in TBO, they
must contain the capability to predict trajectories. However, different DSTs will in principle rely on different trajectory predictors (TP), which may produce different, inconsistent trajectories for the same flight. This lack of consistency among predictions is seen as a key issue for the integration of current and future DSTs. Coordination between TPs is the key to ensure coordination between air-ground, ground -ground and air-air DSTs and hence the successful evolution and application of the TBO concept.
This thesis proposes a standard method to describe trajectories that can allow different DSTs to express and exchange their views of the predicted trajectory of an aircraft. This method, called the Aircraft Intent Description Language (AIDL), provides the necessary
mechanisms to formulate the aircraft intent. The aircraft intent is defined as the unambiguous description of how the aircraft is to be operated within a certain time frame.
Since the mathematical formulation of this concept is needed for the computation of a trajectory, each TP has their own format of aircraft intent. However, the uncoordinated
research in trajectory prediction has driven to different models of this aircraft intent,which has precluded its use to coordinate trajectory predictions of different TPs. The use of the AIDL as an standard mean to describe trajectories permits an easy construction and manipulation of trajectories between different TPs. The scope of this thesis is limited to an AIDL that describes airborne operations of civil aircraft, in particular turbofan and turbojet aircraft. However, the methodology exposed in this thesis to obtain the AIDL can be easily applied to ground operations and other type of aircraft and air vehicles (e.g., propellers, helicopters) to extend the scope and applicability of the AIDL.
The AIDL is characterised by an alphabet and a grammar. The AIDL grammar contains both lexical and syntactical rules. These rules ensure that the aircraft intent contains
the necessary and sufficient information that is needed to compute a trajectory. The development of these rules is based on a rigourous mathematical analysis using Differential Algebraic Equations (DAE) theory. The lexical rules in the AIDL's grammar govern
the formulation of the words of the language by combining elements from the AIDL's alphabet. This alphabet contains a set of atomic primitives, equivalent to the letters in
the English alphabet, called instructions, which capture basic commands and guidance modes at the disposal of the pilot/FMS to direct the operation of the aircraft in the ATM
context. Instructions can be seen as minimal indivisible pieces of information describing distinct ways of closing one of the aircraft motion's degrees of freedom. Mathematically, an instruction is characterised by an equation that is to be satisfied simultaneously with
the equations of motion during a certain time interval, denoted as the execution interval of
the instructions. The words of the AIDL are called operations. An operation represents an
elemental aircraft behaviour that determines its motion unambiguously during a specific
time interval denoted as the operation interval. An operation is the result of a set of
compatible instructions simultaneously active during the corresponding operation interval.
The syntactical rules in the AIDL govern the definition of sentences, which are formed by sequences of operations. These rules allow expressing any possible behaviour that can be elicited from an aircraft in the ATM context.
While each DST may have a different input format to describe aircraft intent, the AIDL is designed in such a way that these different inputs can be seen as 'dialects' of the AIDL.
Thus, the AIDL can be used as a lingua franca by different the DSTs, which would use it as the common standard to communicate aircraft intent with each other.
The possible applications of the AIDL in a TBO environment are manifold. For instance, aircraft intent information expressed using the AIDL could be exchanged as part of a
negotiation process between airborne and ground-based automation systems. Air-air synchronisation based on aircraft intent could permit the coordinated operation of Unmanned
aerial vehicles (UAVs) by means of exchanging their future behaviour expressed as aircraft
intent. Ground-ground aircraft intent sharing would enable a common and efficient treatment of aircraft trajectories in such a way that any amendment could be easily shared
between different automation tools.