Introduction
During the day a person makes hundreds of decisions. Flying an aircraft is no different, the pilot must use his decision making skills continuously. An American diplomat once said:
Only total inactivity will cause no errors Edward Phelps – US Diplomat
The pilot, unfortunately, cannot follow this course of action as the aircraft will eventually run out of fuel. The use of information and decision making is a complicated process. The neural pathway through the brain where information is received, a decision taken and a response executed are too complicated for this course. A simple model of what is called Human Information Processing (HIP) follows.
Sense
A physical stimulus has to be received by the receptors.
Stimulus Receptor
Sight Eyes Sound Ears Taste Tongue
Touch Proprioreceptive System
This raw energy is unusable to the brain and needs to be converted (transduced) into electrical impulses.
Stimulus Receptor
Transduction
Sensory Memory
ATPL Human Performance and Limitations 15-2 27 November 2003 Initially the information is sent to the Short Term Semsory Memory. The time that the information is stored is limited and depends upon the attention that can be paid. Information from the two main senses are held in:
Iconic Memory Visual sensory store which lasts for 0.5 to 1 second
Echoic Memory Auditory sensory store which lasts for 2 to 8 seconds
Once there is enough processing capacity in the brain then the information is passed on to the area of perception.
Attention is paid during each of the following processes. The amount of attention that can be paid to each piece of information is limited as will be seen later in this chapter.
Perception
An interpretation or impression based on one’s understanding of something
Perception is the process by which the brain recognises and interprets the transduced stimulus which has been held in the short term sensory memory. In the perceptive stage the mind starts to build up a mental model.
This entails building a 3-D model which builds pictures in our minds of: ¾ Where we are
¾ Where we are going ¾ Where we have been
It is true to say that our mental model is our conceptual way of understanding: ¾ What an object is
¾ How that object works
¾ What effect that object is going to have in our life
Stimulus Receptor
Transduction
Sensory Memory
Perception is based on the information we sense and our expectations of the world. Perception is based on the following inputs:
¾ The processing capacity of the brain ¾ Past experience
¾ Expectation
Unfortunately, once we have reached the perceptive process it is difficult for us to change our minds. It is at this stage that the human being is most likely to fall into the problem of Confirmation Bias.
Confirmation Bias
Confirmation Bias is part of the human error process that occurs when a false perception is made. It is a situation where a person has made a decision and only believes information that confirms that decision. Any contradictory information is ignored.
For example:
In a two engined aircraft where there is a burning smell in the cockpit. If one engine is shut down and the burning smell goes then it might be fair to assume that the correct engine has been shut down.
If in the above case the conditioning system is taking air from both engines then the burning smell might have gone for another reason and the incorrect engine shut down. In this case the pilot may be tempted to believe that he has shut the correct engine down and Confirmation Bias has been started.
Central Decision Making and Response Selection
Once perception is completed then a decision has to be made. Impulsive or immediate response can be made or the HIP continues with the brain using:
¾ The working memory and long term memory, or ¾ The motor memory system
ATPL Human Performance and Limitations 15-4 27 November 2003
Ultra-short Term Memory
If an immediate response is required then the brain replies on impulse using the “ultra short memory”. This memory can retain sensory inputs for about a second. This does depend on external factors such as strength of impression.
In the ultra-short term memory, material is processed very quickly according to its current importance. Importance or priorities will vary from person to person and with the situation.
Cocktail Party Effect
Cocktail party effect is one way that the brain uses this ultra short memory. A crowded Friday night bar where you are in conversation with friends. You are concentrating on your group when a person behind you says your name. Without altering expression you immediately change your attention to the other group.
Working Memory or Short Term Memory
Both terms are frequently used. Consider the following. If a pilot hears a warning bell on a flight deck then they will probably react in one of two ways:
¾ Switch off the sound in which case an immediate response has been made. ¾ Hold the information in memory whilst a search is made in order to identify the
problem. Stimulus Receptor Transduction Sensory Memory Perception Decision and Response
The above uses a continuous process where information is constantly entered and recalled from memory. During this period a decision has to be made where the information is stored – the short term memory or retrieval from the long term system. The central decision and response channel can only work one problem at a time and is thus a choke point within the brain.
Short Term Memory and its Limitations
When the brain accesses the short or long term memory system the short term memory will store information for a short time.
Used to retain information that is not needed in the long term memory, the short term memory only retains information for a limited period and its capacity is limited to:
¾ 7± 2 unrelated items of information that can be held for approximately 10-20 seconds unless active rehearsal is used to retain the information.
¾ A process called “chunking” can increase the number of items.
Stimulus Receptor Transduction Sensory Memory Perception Decision and Response Short Term Memory Long Term Memory
ATPL Human Performance and Limitations 15-6 27 November 2003 eg the use of telephone numbers
¾ A telephone code 041 is held as one item not three ¾ An area code 01455 is held as one item not 5
¾ 01455 477686 would be retained as 2 items not 11 which would overload the short term memory
Short term memory is prone to interference and any interruption can and will cause the loss of information.
For example:
You need to phone a person but do not know the number. You look it up in the phone book and start rehearsing it as you go to the phone. Before getting to the phone you are interrupted for about 30 seconds by something. The short term memory loses the phone number and you have to start all over again.
Environment Capture
The short term memory is prone to a problem known as environment capture. A frequently operated skill in the same environment (a habit) where the pilot has not made a conscious decision to operate the skill.
For example:
When flying in the traffic pattern. Pilots who delay undercarriage selection somehow have this information dislodged from the working memory especially if the delay is by some form of interruption like ATC instructions. The event will generate a standard response from what becomes a boring activity, flying several uneventful circuits. The pilot may make the final gear down call because he always makes it at this time. The mental model is completed and the pilot believes he has selected gear down. Only when the aircraft scrapes down the runway does the pilot realise that he has failed to select the gear.
Long Term Memory and its Limitations
Long term memory has two distinct parts:
Semantic Memory This is the store associated with what we know and do: the understanding of a word; how to fly an aircraft; facts - London is the capital of England.
This area of the brain stores all the information that is learnt, including that information we will never use. If a word or fact is forgotten it is because the neural pathways are forgotten, not that the information is lost. The information is stored in an area of the brain that has not been accessed for a long time.
Episodic Memory Episodic memory is a fluid memory that remembers events that have been experienced. It is coloured by our desires and expectations. Stories are not remembered factually but reviewed and changed to suit the teller’s needs. In eye witness reports episodic memory can have problems. Think about the reporting of aircraft crashes:
¾ All aircraft burst into flames before they crash
¾ All pilots fly the aircraft away from schools, hospitals and houses before they crash
Other problems occur with the “expert” witness. A pilot witnessing an aircraft crash has expectations of what was happening in the cockpit and will relate these as what he saw. A non-expert witness is more likely to give a better account. Children give the best eye witness reports as their episodic memory has not yet developed.
Motor Memory
When a new action is learnt then it initially seems difficult. Like riding a two wheel bike for the first time. Piloting is exactly the same, initial impressions of flying, ATC etc seem to make the task impossible when training is started. Like most actions which are well practised flying is eventually executed by a motor programme. Non conscious actions are used to fly the aircraft whilst talking on the radio uses conscious thought through the decision and response channel. The motor programme is by-passing the central decision and response channel.
ATPL Human Performance and Limitations 15-8 27 November 2003 A motor programme can be used when an action has been well practised and is repetitive. The performance of this action becomes automatic and no conscious thought need be applied. The process by which motor programmes operate is complex but as soon as the flying becomes difficult eg landing, the central decision and response channel has to be used to fly the aircraft.
Action Slip
The advantages of using motor memory is obvious, as it extends our capabilities. Action slip is an error process that is caused by the brain using motor memory.
For example:
Pouring a cup of tea, whilst watching TV, and then adding sugar to the cup. If there is some distraction on the TV we can find ourselves pouring tea into the sugar bowl. The action of pouring the tea is being carried out by a motor programme, with no conscious thought being applied. With the distraction the process of pouring the tea carries on and we start pouring the tea into the sugar bowl because the brain thinks it has progressed to the sugar stage, or:
BAC 1-11; My first officer was flying the leg. After T/O I carried out the usual checks. Brakes, U/C up, PAX notices off etc. Weather lovely, blue sky. W/V 270/18, temp +30C! At 1500 ft I
Long Term Memory Stimulus Receptor Transduction Sensory Memory Perception Decision and Response Short Term Memory Motor Memory Response Execution
noticed the flaps were retracted. I thought the F/O had retracted them early. Usually the flap is retracted at 200 ft plus in VFR or 3000 ft noise abatement. Almost immediately he mentioned that the flaps were retracted. "Oh, I see you have brought the flaps in" he said. "No", I replied, "I haven't touched them". He said that he hadn't either. Shortly after this he noticed the U/C was still extended. I raised it. There can be no doubt I raised the flap instead of the U/C after take-off. I had no memory of this. Why would I do this potentially dangerous thing on an aircraft with which I was completely familiar? I have no idea; no sickness, no stress, nothing dramatic personally.
Response Execution
Once the memory has been used the brain has to make a response. How appropriate the response depends upon the pressure that a person perceives that he is under. The following apply to decision making in all walks of life:
¾ If a delay is dangerous then a person will feel that they are under pressure to make a quick decision
¾ Quick decisions are usually made before all information is processed ¾ Where there is stress then a fast but less accurate response is made ¾ Sound stimulates the mind better than sight
¾ Where a person plans for the expected then it is possible that if there is any change then pressure will make the brain reply with the planned response
A crew planning for runway 13 from take off to landing. Only when they contact tower is runway 31 given as the landing runway yet they still land on runway 13.
¾ An old person may react more slowly than a young person yet the response is usually more accurate
Attention
Attention is a limit to HIP, it depends upon certain factors:
¾ The limit to the number of items working memory can hold.
¾ The rate at which information can be passed through the central processing system.
Whether attention is paid to a stimulus depends upon: ¾ The importance of the stimulus
ATPL Human Performance and Limitations 15-10 27 November 2003 Attention can be described in two ways.
Selective Attention
Selective attention is where inputs are sampled and given a priority. Detailed processing can only be carried out on one complex task. If there are too many demands on the attention then information will be lost.
In 1972, a Tristar on approach to Miami experienced a minor undercarriage malfunction. The crew selected the auto-pilot and looked into the undercarriage problem. Unfortunately, the auto-pilot setting was such that the aircraft entered a shallow descent. As the aircraft approached the ground, ATC, other aircraft, visual and audio warnings tried to attract the crew's attention to their danger. The crew's attention was focused on their undercarriage problem and were filtering out all other warnings, until it was too late to do so. The aircraft crashed killing all on board.
Divided Attention
Divided attention can be used to carry out two tasks that do not overload the HIP.
Motor programmes, which are run with no conscious thought, can be consciously checked by a pilot who diverts his attention away from the major task in order to check a sequence of operation.
Stress and Attention
Stress focuses the attention processes. Thus to complete a task, under stress, we focus entirely on that task in hand. This is always to the detriment of other problems.
Response Behaviour
Once a response has to be made the brain will use one of the three response behaviours.
Skill Based Behaviour
Skill based behaviours are procedures acquired through practice and that are executed without conscious thought. Skill based behaviour is obtained in two distinct manners:
¾ Concentration on the individual parts of a skill, giving them attention, until practice makes the individual processes second nature.
¾ Practising the whole skill with concentration on the final product. Eventually a motor programme is made which carries out the skill based response.
Once these skills are acquired then they seem to possess certain characteristics:
¾ The skill is not easily explained to others. This may cause difficulties if a pilot wishes to pass on the skill.
¾ If the skill needs to be modified then the component parts must be broken down and re-learnt.
Because of the uses of motor programmes in skill based response a pilot operating a skill makes the decision to do so and then has the attention to monitor the task. But if a distraction is introduced then the pilot may make an inadvertent operation. Environment Capture can also occur in skill based response.
All actions need to be consciously checked, especially those that are using sub-conscious thought.
The errors of skill do not normally happen to the student pilot; they happen to a pilot with experience.
Rule Based Behaviour
Rule based behaviour uses the short and long term memory to carry out actions. Rule based behaviour is stored in the long term memory and involves the use of the central decision and response channel. By using conscious thought the error problems that occur with motor memory skills are bypassed.
Simulator, procedural training or similar work that involves the use of Flight Reference Cards and checklists or plates are examples of this type of behaviour. The only problem relates to the well known saying:
Garbage in – Garbage out Knowledge Based Behaviour
Knowledge based behaviour is based on the reasoning powers that a person can use to arrive at a decision. The pilot is able to use his own thinking processes to evaluate and then reach a decision.
Feedback
When carrying out a task then we must continuously monitor the consequences of our actions. To enable the information to be processed, both internal and external feedback mechanisms are used.
ATPL Human Performance and Limitations 15-12 27 November 2003 Intentionally Left Blank