The technical exploitation of aircraft is carried out through a process of sequential changes in organizational and technical states. Technical states correspond to changes in the technical quality of the aircraft as an operational object [1,2,3]. Organizational states are associated with the processes of organizing and utilizing aircraft at various stages of their technical exploitation, including the phases where the aircraft is:
– at its home (base) airport; – in flight; – at a transit airport; – at an airport of the transit base type; – outside the operational management contour of its technical exploitation.
The sequence of transitions and stays of the aircraft through these stages of its technical exploitation is determined by a number of factors [1,2]:
the demands for aircraft utilization generated by the flight phase, characterized by the parameters of the flight schedule within the airline network; the necessity for aircraft recovery outside the operational management contour of the aircraft fleet’s technical exploitation (including periodic technical exploitation and/or maintenance, etc.); the need for aircraft recovery at the airports of the airline network, prompted by changes in the aircraft’s state during flight operations; the opportunities for aircraft recovery at the airports of the airline network; the list of permissible failures reflecting the structural and operational properties of the aircraft.
The technical exploitation of aircraft includes [2]:
ground maintenance of the aircraft; airborne technical exploitation during flight (in the air).
For each of these, there is a characteristic set of states that may be represented in the form of graphs containing a specific set of nodes and transitions [4]. The nodes (vertices) of the graph correspond to tasks, while the edges represent relationships between tasks. Such graphic models facilitate the identification of quantitative relationships between nodes to improve the processes of aircraft technical exploitation through statistical research methods [5].
Operational management of technical exploitation processes involves the continuous monitoring of parameters of the aircraft technical exploitation process and adherence to the dispatch schedule for aircraft utilization [6]. The operational control loop is based on the model of aircraft technical exploitation processes, presented in the form of technological chains consisting, in turn, of technological elements related to the aircraft utilization process at various stages. Therefore, a crucial aspect of describing the aircraft technical exploitation process, in addition to describing its structure, is describing the mechanism that determines the sequence of transitions and stays of the aircraft in different states at various stages of technical exploitation [1,2].
Each route within the airline’s network, taking into account intermediate landings between the base (initial) and final destination airports, consists of B – Base Airport (serves as the initial and final airport on any route), T – Transit Airport (facilitates intermediate stops but not necessarily equipped for extensive recovery operations), TB – Transit Base (facilitates intermediate stops, is equipped for extensive recover operations).
The airline’s information base contains the necessary probabilistic and other data required to reduce the risks of departure delays at these airports due to the need for aircraft recovery [8], as shown in Table 1 [9].
Probabilistic and Other Data for Airports in the Airline Network [9]
Characteristic | Airport Type | |||
---|---|---|---|---|
T | TB | B | ||
1 | Probability of Availability of Spare Parts Required for Aircraft Recovery | |||
2 | Probabilistic Characteristics of Aircraft Recovery Time ( |
|||
3 | Probabilistic Characteristics of Operational Delivery of Required Spare Parts in Case of Their Absence at the Airport ( |
|||
4 | Availability of Specialists for Aircraft Recovery Work | No | Yes | Yes |
5 | Average Aircraft Ground Time at the Airport |
The structure of network flights for an airline with the provisional name “RAF” is presented in Table 2. Each flight route within the network consists of a sequence of flights with layovers at airports of different types.
Structure of the airline network routes for RAF
Flight Route Structure (Graphical Representation) | Flight Parameters | |
---|---|---|
1 | B – T – B | 1/2 |
2 | B – T – T – B | 1/3 |
3 | B – T – T B – B | 1/3 |
4 | B – T – T – T – B | 1/4 |
5 | B – T – T – TB – B | 1/4 |
6 | B – T – TB – T – B | 1/4 |
7 | B – TB – TB – T – TB – B | 1/5 |
8 | B – TB – B – TB – TB – B | 1/5 |
9 | B – TB – T – TB – T – TB – B | 1/6 |
10 | B – T – T – T – TB – T – TB – B | 1/7 |
11 | B – TB – T – TB – T – T – TB – B | 1/7 |
12 | B – TB – T – T – TB – T – TB – B | 1/7 |
Let – The proportion – The ratio
Definition: By “state of the aircraft in-flight,” we mean situations that arise when an aircraft is in a normal flight mode, but affected by one or more adverse factors, leading to diminished level of flight safety l. In this context, adverse factors are exclusively considered as failures of aviation equipment [10,11].
In general, the “state of the aircraft in-flight” encompasses a combination of aircraft properties and psychophysiological indicators of pilots, which are subject to change due to the impact of adverse factors affecting the aircraft, leading the flight mode to deviate from the “normal” state. Regulatory documents categorize these deviations as “special situations” [10,11]. According to these documents, there can be four potential special situations in flight: complicating flight conditions (CFC), a complex situation (CS), an emergency situation (ES), or a catastrophic situation (CatS), see Fig. 1.
Transitions from the normal state (
The identification of specific failures during flight and their impact on flight operations is guided by a list of permissible failures, which classifies the aircraft’s states into several categories for managing aircraft recovery within the airline network [8,10]:
Figure 2 presents a diagram of possible transitions of the aircraft through states
To describe the dynamics of an aircraft’s state within a given airline network structure, it is necessary to account for the processes of changes in state during each flight on a specific route, and the sequence of flights within the timeframe of the aircraft’s presence in the operational control loop of the technical exploitation process, under certain assumptions.
In-flight, the aircraft’s state does not improve. Departure for a flight (i.e., from an airport of type B) is allowed only in states Departure for a flight from airports of types T and TB is allowed in states
According to Figure 2 and Table 1, the possibilities for aircraft recovery at airports are as follows [11]:
– At airports of type B, states – At airports of types T and TB, state
Thus, the differences between airports of types T and TB essentially boil down to variations in the characteristics
The recovery of the aircraft state at airports within the airline network and the occurrence of departure delays, driven by the need for aircraft state recovery, are influenced by several factors:
The emergence of recovery demand, generated by changes in aircraft state during flight. The conditions and organization of aircraft recovery at the airports within the airline network, which can be described using the characteristics provided in Table 1. The permissible failure list, i.e., the presence of states
According to the definition of aircraft states, the following regeneration cycles are associated with aircraft state recovery [8,14]:
For state For state For state
The regeneration cycles of aircraft states in the process of their technical exploitation is presented in Figure 3 as graphs of aircraft recovery [5], for airports of type “B,” “T,” and “TB,” respectively.
The need to restore aircraft states at airports within the airline network is prompted by in-flight situations related to technical failures, leading to possible departure delays.
Two main mechanisms can be identified for the formation of such delays:
The first mechanism is characteristic for airports of type “T” and “TB” and involves the following:
When a need for aircraft recovery arises, it is contingent upon the availability of the necessary spare parts at the airport. The overall duration of aircraft recovery in this case is described by the recovery time distribution function If the required spare parts are not available, the parts must be delivered through available channels, and the duration is determined by the distribution function The second mechanism, in turn, is characteristic for airports of type “B” and is related to the probability of including the aircraft in the next flight route.
If the aircraft is indeed slated for the next flight route, unlike the first mechanism, the probability If the aircraft is not included in the next flight route, it is assumed that situations leading to departure delays do not occur.
If the total duration of aircraft recovery (under both the first and second mechanisms) does not exceed the aircraft’s parking time (