How An Aircraft's Primary Flight Display Supports Pilot Situation Awareness

About SA in aviation

Many of the accidents nowadays are caused because of the loss of SA. This is happening when the pilots are not realizing that a safety-critical occurrence took place. The pilots sort any event in their mental model of the situation and try to solve the occurrence using the information that recalls in the brain. Perceiving the lost of SA triggers when the pilot realized that the followed pattern is false, and it is not applying to the current environment.

Using the three levels model of SA presented by Endsley, actions made during the take-off procedure could be divided. The first level of SA describes the observation and perception of the elements, in the actual case, the outside environment like airport, weather and runway and the inside environment described as the information given by PFD. The second level of SA involves comprehension, the interpretation, and understanding of the critical information from PFD. Last level, the third one of SA deals with a prediction about the near future and possible actions or events in the environment.

Take-off procedure

Taking into consideration the Airbus A320 PFD design, the pilot should be aware of some functions that PFD’s offering in order to ensure the safety of procedures, also to monitor some data, in order to predict future actions that have to be done.

For a better explanation of SA awareness during take-off procedure, some steps could be described as follows:

1. Shortly after increasing the engine power, a speed trend appears on the PFD.

This is very useful in order to know the estimation of the speed in 10 seconds. The pilot has to monitor this speed in order to know when it is safe to take-off. Firstly, when reaching 100kts they have to read it and to acquire the information. Shortly after, two more indicators appear on the screen, the V1 defined as the speed beyond it’s not recommended to abort take-off, and Vr – defined as the speed where the pilot has to use the stick in order to nose-up the aircraft.

Referring to the SA and Endsley model in this timeframe, some of the situational elements as speed, and signs are perceived and stored in the short-term memory.

After the information is processed from the visual point of view, the brain calls the corresponding knowledge about the situation. This is the link between the first level of SA where the information is just perceived as visual, and the second level of SA, where the brain offers information to the pilot about the procedure and what needs to be done. Because of the training and knowledge of the procedure, the pilot is able to predict the further steps which are necessary to be conducted. This loop is going from level two of SA to level three of SA in a dynamic system because the interpretation and understanding of the current situation are strongly linked to the next steps. After that, level three of SA is going back to level one, where the pilot perceives again the current situation of the aircraft, just after the input commends.

2. After reaching Vr, the pilot pulls the stick in order to nose-up the airplane.

PFD is used in order to monitor the attitude level, speed indications, and altitude. At this point the visual distribution is very important as the mental workload is increasing. There are multiple things to be monitored at the same time, as well as indicators of different modes. Situational awareness in this timeframe is the highest in level 1, decreasing slowly as the pilot absorb and perceive the information – level 2 of SA and predict next steps – level 3 of SA.

3. Once reaching a certain speed and altitude, the automation takes place and some modes are activated:

• a. Navigation ON(NAV) – shows that the aircraft will fly the programmed flight path
• b. Climb thrust & Climb mode
• c. Auto thrust engaged

Level 1 SA involves the visual monitor and get the information from PFD. Then the pilot must understand all the changes made on the screen and prepare for the next steps. During this time, the workload is still high, and the pilot has to be sure that the transaction between manual mode and autopilot doesn’t reduce the performance and SA.

4. In the time that the speed is increasing constantly, there are also two important steps to be made, in order to increase the speed limitations.

There are two letters that, when comes on the screen, the pilot must acknowledge them and retract the flaps and the slats. The letter F indicates the minimum speed for flaps retraction and letter S indicates the minimum speed for slats retraction. Taking into consideration the same three-level of SA developed by Endsley, on level 1 the pilot in command must be aware of the PFD messages and verbally confirm that the minimum speeds were approached. For experienced pilots, this 4th step should be predicted right after gaining the necessary speed for take-off, as it’s mandatory to be done on every take-off procedure. This put in evidence how the loop from level 3 of SA, which stands for prediction, get back to level 1 of SA.

5. After retraction of slats, the aircraft could speed up to the standard speed below flight level 100 – FL100.

During this period, when passing the transition altitude, pilots have to change the QNH pressure to standard (STD). Again, PFD is helping the pilot to maintain situational awareness and high safety standards by showing an alert when the FL060 was reached. Because of the workload decrease, there is also an improve in SA, in the way that the pilot may focus more on the PFD after finishing the necessary steps for take-off.

Micro-cognition

Taking all those steps into consideration, the conclusion about how PFD supports the pilot situational awareness could be drawn. During the take-off phase, there are many safety-critical phases that take place in a short period of time. The pilot must acknowledge a lot of information and it’s incredibly helpful to have most of it on the same system. Because of the high workload, sometimes SA decreases, as many of the processes have to be manually done and still monitored for any other further actions.

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Sensors as eyes and ears perceive the information and the long-term memory combined with skills and training conduct the human to have a response on each situation.

Because attention is limited, sometimes pilots are stressed. (Braune and Trollip, 1982) states that working memory is very important, allowing the pilot to modify attention deployment based on its goals. Relating this one to PFD, the pilot may check different parameters during each phase of take-off. This is also affecting the SA in the way that pilots may face a significant reduction in accuracy and a long time is needed to perform actions. SA is limited when the pilot must perceive many items in the same time with strong accuracy. By using long-term memory, the information may be processed faster, which means that the transition from Level 1 SA to Level 2 and 3 SA could me made faster, due to short time taken of interpreting data.

An important finding shows that the attention could be manipulated, so the PFD could be designed in the way that the pilot could see the notifications due to pop-ups. After the information is processed, it become more and more easier for the pilot to proceed with the actions, because after the information is stored in the short term memory, goes to the long-time memory, so next time facing the same situation, the memory for skills is called and the same maneuver can be done in shorter time.

Combining the Endsley model and Baddeley model for working memory, all levels of SA could be described using Phonological and Visuo-spatial loops.

The phonological loop helps the pilot to acknowledge the information during a take-off check with the help of PFD. Firstly, they read the words (i.e. FL100), after they spoke them out to check it with the other pilot. This loop helps for improving the long-term memory and to prepare yourself for the next steps that need to be done. Once perceiving the information (Level 1 SA), the brain stores it in the working memory and with help of existing knowledge, the information is understood (Level 2 SA) and future decisions occurs in the working memory (Level 3 SA).

Visuo-spatial loop combines spatial locations with information that is seen by the pilots on PFD (i.e. the pilot sees on PFD that needs to pull-up the stick right after passing some points from the runway) – Level 1 SA. After storing information and understanding it, the pilot must act properly, doing appropriate actions for the next steps – Level 2 and 3 SA.

Combining all the information and storing them in the brain, the long-term memory is updating the information every time. For example, the pilot recognizes the system messages that comes out in a particular moment during take-off procedure (form level 1 SA). Every message or sign could be linked to a particular situation during this phase (Level 2 SA). Using the long-term memory, the pilot can take actions in accordance with the mental model developed during time (Level 3 SA). Having the high-level of SA, the pilot develops a strongly and precisely scenario which allows him to know the exact time and moment when he must do the actions.

Developing the mental model while acquiring experience, the automaticity tends to appear. Then, the processes tend to be done faster, without lot of effort. In the case of take-off, the automaticity helps pilot in dealing with limited attention capacity in the way that the pilot could already know what needs to be done in certain moments.

This process involves the Central Executive system which connects all the data and prioritizes the attention to the most important tasks first. It could be strongly linked to the Endsley model of SA, more exactly the SA level 2 and 3. Central Executive supports Level 2 SA in the way that the relevant information is selected from PFD and stored in the working memory subsystems. Combining perceived information with task-relevant information given by long-term memory, the Level 2 SA is involved in creating the mental model of procedure. Aretz (1991) found that the pilot SA during navigation is highly supported by the Visuo-Spatial subsystem. When the workload increases, the pilot tends to use both subsystems in order to support performance during take-off procedure. The highest level SA is achieved by the pilot when the execution process starts, involving as well the Level 1 and 2 SA, because the maneuvers must be observed and any change in the system must be usually in the same way that the pilot is expecting to be.

Because there are not many pieces of evidence on the power of the central executive, the capacity and length of storage in the long-term memory couldn’t be measured. Having the interferences in the cockpit such as noises or other systems messages, the PFD is designed to help the pilot to restart the memory processes and to re-call the central executive by reinitiating the Phonological and/or Visuo-Spatial loops.

Conclusions

In order to avoid SA errors in the take-off procedure, the pilots firstly need to monitor and observe any available information on PFD. The SA errors could be identified quicker in the novice pilots’ actions, because their long-term memory may not store as much information as an experienced pilot does. In order to enhance the performance and situational awareness, training programs may be applied, especially in safety-critical phases of flight like take-off. Due to training and experience, the projection of future aircraft states (level 3 of SA) are not sometimes anticipated well by novice pilots. This is because of inflexibility to scan visually all data from the PFD. An experienced pilot could deal better with situational awareness due to his scanning capabilities, as well as interpretation of the data and prediction of future steps.

PFD is designed in a way that all necessary information could be communicated to the pilot in a logic manner. It also helps to monitor the short and long-term expectations, after the input on the system is made. By distributing attention, the human could benefit from real feedback over the actions performed and safely maintain the high level of SA.

References

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