EVACUATION OF AIRCRAFT ON LAND

Conclusion: A proper evacuation strategy and the fastest evacuation of occupants are crucial for saving lives. Simulation software use in evacuation problems presents a very effective way in terms of safety, cost-effectiveness and prediction. This kind of software presents an obligatory engineering tool for more effective and more precise dealing with evacuation and similar problems. This paper was written to show how simulation software can be used for calculating evacuation times from an airplane on land.


Introduction
Evacuation of people, animals and material resources from endangered places or buildings to a safe location in a fast and safe way always presents a complex task.
Generally, traffic presents a very important social activity where potential situations and occasions demand very effective evacuation strategies. According to reports and statistics, air traffic presents one of the safest ways of traffic. Most accidents in air traffic occurred in the air during taking off and landing. A diagram of all accidents in civil air traffic from 1919 till October 1921 is presented in Figure 1 (Planecrach, 2021). One of the most important advantages for air traffic in terms of safety are rigid procedures and rules for aircraft and high scientific and quality levels used in manufacturing aircraft. But accidents do occur. Sometimes, it is possible to avoid accidents or to reduce consequences of accidents. Of course, the most important course of action in any case of damage, malfunction or any problem, is to land the aircraft immediately. Many accidents were avoided by forced landings, very often out of the runway. A well-known case called "Miracle on the Hudson flight" occurred in January 15, 2009, when a commercial airplane landed on the Hudson river and all 155 passengers and the crew members survived (CN Traveler, 2022). However, even when an aircraft somehow lands, a very important moment is to evacuate the passengers from the airplane to the safety. Potential scenarios can be different: an engine GLASNIK / MILITARY TECHNICAL COURIER, 2022, Vol. 70, Issue 4 failure while taking off, missed runway while landing, wheals failure while taking off or landing, outing of the runway, etc. This task can be very hard, depending on many factors. In many cases, passengers try to evacuate the aircraft without any kind of organisation, tactics or plans; the presence of fear and panic is huge and injuries and even deaths are very likely to happen. Also, very often, the cabin crew do not have precise and continual connection and communication both between themselves and with the passengers which implies a delayed or considerably longer evacuation. The fact that the aircraft must be evacuated immediately is disturbing enough in its own right, but in the presence of other phenomena such as fire, smoke, sparking, etc., the whole situation becomes extremely tense and likelihood for accidents significantly increases. Generally, evacuation from a landed aircraft can be realized by emergency exits which can be equipped with stairs, emergency slides and emergence ropes (SKY Bary, 2022).
Therefore, for safe and effective evacuation, it is very important to know which evacuation strategy to apply in different situations: in which direction to go, which exit to choose, how fast to go in order to avoid the jams and crowds, etc. In a situation such as force landing or a bomb threat, these tasks can be very hard to realise because of the presence of many different factors such as fear, stress, panic, lack of time, etc. It would be thus best to somehow predict as many potential scenarios as possible and calculate potential evacuation times. All of this is possible with the use of simulation software. So, this paper was written to show the advantages of simulation software use in the prediction of evacuation. The main motive and the aim of evacuation is to save human lives. The most important advantages of simulation software use are to calculate times needed for evacuation from aircraft in different situations and scenarios and predict a lot of potential situations and scenarios in a safe, inexpensive and effective way. The number of all potential scenarios is huge and it is almost impossible to predict all potential scenarios, but with use of simulation software a lot of scenarios can be realized and analysed so that the knowledge and results gained in that way generally significantly improve a degree and efficiency of evacuation. The main contribution of this work is in prediction -in determining the best evacuation scenarios for occupants in some real situations by using simulation software. The use of the simulation software method for predicting evacuation is still a novelty and a method not used enough for determining evacuation scenarios and calculating evacuation times. The use of simulation software is safe for human lives because real occupants are not involved. It is also very cost-effective Jevtić, R., Evacuation of aircraft on land, pp.972-992 because it does not require the use of different material resources. And, of course, it is very precise because simulation software uses checked algorithms for calculations with the influences of many different factors (speed of occupants, stairs dimensions, number of occupants, etc.).

Pathfinder simulation software
The main method used in this paper was the simulation method. Although computer-based simulations have been used in last 20-25 years, it is still a method not often used (Galea et al, 1998). Simulation is possible by the use of proper simulation software, called Pathfinder software, version 2021. There are very important reasons for simulation software use in evacuation. Safety is above all. It would be almost impossible in reality to design and test evacuation scenarios without accidents and even victims and material resources destruction. Then comes accuracy. The software of this kind shows a great degree in precision and accuracy. In addition, the time needed for calculating the whole simulation is significantly shorter than the time needed for a simulation without simulation software.
This powerful simulation software provides simulations of people moving along various passageways such as stairs, elevators, or ramps with different speeds of occupants. There are two different simulation modes: a so-called SFPE mode and a steering mode. One of very important characteristics of this software is to "import" files from other programs which significantly increases the compete simulation process because in that case it is not necessary to draw the environment (Thunderhead, 2017;Jevtić, 2021 The evacuation from the aircraft was simulated with two different scenarios: using ordinary stairs for passengers and using emergency slides. For the first scenario, there were three different simulations realized: with one front door opened, with two doors opened (the front and the back ones) and with three doors opened. All used doors in simulations for this scenario were on the same side of the aircraft. Although there are four doors on both sides of the aircraft, in real situations at airports, mostly one or two entry/exit doors with stairs are used. The speeds of passengers/occupants were 0.2 m/s, 0.3 m/s, 0.4 m/s, 0.5 m/s, 0.75 m/s, 0.95 m/s and 1.15 m/s. These speeds were chosen because of the lack of space in the aircraft for bigger speeds and the existence of seats and a narrow aisle in the middle of the aircraft.
For the second scenario, there were eight different cases simulated. The first case involved all eight doors opened; the second case involved one door closed and seven doors opened; the third case involved two doors closed and six doors opened; the fourth case involved three doors closed and five doors opened; the fifth case involved four doors closed and four doors opened; the sixth case involved five doors closed and three doors opened; the seventh case involved six doors closed and two doors opened, and the eighth case involved seven doors closed and one door opened. For each of seven cases, the emergency slides were used. The simulation model of the A 321 aircraft with its interior is presented in Figure 2 in Pathfinder software while the emergency slides of the aircraft marked with numbers from 1 to 8 are presented in Figure 3. Many details in figures could be visible if the HIDE function were not activated.

Simulation results
All simulation results for this paper were realized on a laptop Dell Latitude, with Intel® Core™ i7-1185G7 (4 Core, 12M cache, base 3.0GHz, up to 4.8GHz, vPro) processor and 16 GB of RAM memory. It is recommended to use a computer with "strong" hardware support for work with simulations.
Some simulation moments are presented in Figures from 4 to 7, while the simulation results are given in Figures 8 to 25.
Because of a huge number of realised simulations and the paper limitations, only the results for the fastest and the slowest possibilities for every case of the second scenario were presented. Analysis of the results The total number of realised simulations was 255. The first scenario involved evacuation from the aircraft but with the use of ordinary stairs, for noted speeds of passengers/occupants. The second scenario involved evacuation with the use of emergency slides. Because of eight doors with eight emergency slides, every potential combination of opened/closed doors was simulated. Of course, due to the paper limitations, only the fastest and the slowest possibilities of seven cases of the second scenario were presented (the first case of the second scenario had only one possibility).
The realized results for the first scenario showed that the longest time needed for a complete evacuation of the aircraft was for the case where one door was opened and one staircase in use, for the passengers/occupants' speed of 0.2 m/s and it was 1137.4 seconds ( Figure 8). The shortest time needed for a complete evacuation of the aircraft was for the case where three doors were opened and three stairs in use, for the passengers/occupants' speed of 1.15 m/s and it was 132.4 seconds ( Figure 10). These times are in line with similar calculated and realised times on other similar aircraft types.
There were a lot of potential possibilities needed for some cases from the second scenario, such as the second, the third, the fourth, the fifth, the sixth and the seventh possibility. Because of the paper size limitations, only the fastest and the slowest possibility for every of the noted cases of the second scenario would be presented. It was necessary to analyse this huge number of potential possibilities in order to comprise all potential cases.
There was only one possibility for the first case of the second scenario where all available doors/exits were opened. The shortest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 1.15 m/s and it was 42.9 seconds. The longest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 0.2 m/s and it was 122.7 seconds (Figure 11).
There were eight possibilities for the second case of the second scenario. The shortest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 1.15 m/s and it was 46.6 seconds, when the third or the fourth or the fifth or the sixth door was closed (Figure 12). The longest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 0.2 Jevtić, R., Evacuation of aircraft on land, pp.972-992 m/s and it was 134.7 seconds, when the first or the second doors were closed (Figure 13).
There were twenty-eight possibilities for the third case of the second scenario. The shortest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 1.15 m/s and it was 48.8 seconds, when the first and the seventh doors were closed ( Figure  14). The longest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 0.2 m/s and it was 178.9 seconds, when the third and the sixth doors were closed (Figure 15).
There were fifty-six possibilities for the fourth case of the second scenario. The shortest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 1.15 m/s and it was 64.8 seconds, when the second, the fourth and the seventh doors were closed ( Figure 16). The longest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 0.2 m/s and it was 191.3 seconds, when the third, the fourth and sixth doors were closed ( Figure 17).
There were seventy possibilities for the fifth case of the second scenario. The shortest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 1.15 m/s and it was 79.4 seconds, when the second, the fourth, the sixth and the seventh doors were closed (Figure 18). The longest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 0.2 m/s and it was 221.6 seconds, when the third, the fourth, the fifth and the sixth doors were closed (Figure 19).
There were fifty-six possibilities for the sixth case of the second scenario. The shortest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 1.15 m/s and it was 100.8 seconds, when the second, the fourth, the sixth, the seventh and the eighth doors were closed ( Figure 20). The longest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 0.2 m/s and it was 276.2 seconds, when the third, the fourth, the fifth, the sixth and the seventh doors were closed ( Figure 21).
There were twenty-eight possibilities for the seventh case of the second scenario. The shortest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 1.15 m/s and it was 127.5 seconds, when the second and the fourth doors were opened ( Figure 22). The longest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 0.2 m/s and it was 348.25 seconds, when the first and the second doors were opened ( Figure 23). There were eight possibilities for the eighth case of the second scenario. The shortest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 1.15 m/s and it was 208.5 seconds, when the third door was opened (Figure 24). The longest time needed for a complete evacuation of the aircraft was for the passengers/occupants' speed of 0.2 m/s and it was 376.65 seconds, when the second door was opened ( Figure 25).
It is very important to note that the speeds of passengers/occupants were the same for all of the realised simulations, which is almost impossible in real situations because of a lot of factors such as fear and panic, different anatomy, positions, group and individual behaviour and many others. As an example, fear and panic can have a significant influence on human behaviour in terms of disorder and confusion, which directly implies an increase in evacuation time, accidents and even death epilogues (Kady & Davis, 2009;Deng, 2016).
In comparison to other similar papers, it is important to add that the realised simulation results were in line with similar realised simulation results, although the jam effect on a complete evacuation times has not been taken into account. In comparison with similar simulations realised in the simulation model of the Airbus A330-300 aircraft, the evacuation times were shorter in cases when several doors/exits were available (42.9 to 48.8 seconds against 50 to 59 seconds). These results were expected because the Airbus A330-300 has 285 passengers (Choochart & Thipyopas, 2020). Also, in the comparison with similar scenarios realised on the SSJ-100 aircraft, similar results were expected and realised, taking into account all potential differences between scenarios and aircraft with slight differences (79.4 seconds against 92 seconds) (Suharev et al, 2020). Moreover, it is very important for an evacuation strategy and evacuation times to know the cause for an evacuation (fire, bomb threat, forced landing, fumes, etc.).

Conclusion
The results realised in this paper showed the evacuation times for two different scenarios with the use of stairs and emergency slides. The use of simulation software in the solutions of evacuation problems is of great significance. The most important advantages of simulation software use in evacuations are efficiency, cost-effectivenesss and safety. For some situations, of course, it is almost impossible to determine all potential evacuation routes and to calculate all evacuation times, but, with the use of this software, it is possible to calculate evacuation times Jevtić, R., Evacuation of aircraft on land, pp.972-992 for different evacuation routes and for different speeds of occupants. Also, it would be almost an impossible task to create a real model of the aircraft and test all potential scenarios with real humans as passengers with different speeds in a safe, precise and inexpensive way.
The main contributions of this paper are in calculating evacuation times for different speeds of passengers/occupants and in determining which combinations of opened/closed doors/exits are the most effective. In case that an aircraft must land immediately, many failures can occur so passengers cannot use all predicted exits. Therefore, it would be very useful in some real situations for passengers and crew members to know how to behave, organise and where and how fast to go in order to leave the aircraft in the fastest and safest way.
Future investigations would be directed towards calculations of evacuation times and predictions of evacuation routes with the presence of children, immobile or hard mobile persons, crowd and jams potentials and consequences, etc inside the aircraft. These calculations and simulations will provide proper evacuation strategies and precisely calculate potential evacuation times even in these cases, taking into account all potential factors (speed of hard mobile or immobile persons, dimensions of wheelchairs, etc).
Simulation software in evacuation presents a very important engineering tool with important advantages and its use for complex evacuation problems is mandatory.