CNS/ATM resource kit – Chapter 8: Human factors

The original goals of human factors (HF) were to optimise human and system efficiency and effectiveness. As such, the term human factors, refers to the many issues whether personal, social, environment or organisational that affect how people perform tasks in their work and non-work environments. Within aviation, HF has been focused predominantly on error reduction, either through engineering in safety and efficiencies or through training and monitoring (checklists).

The intention of this chapter is to highlight some of the HFs that may impact those operating a GNSS, explore situational awareness, managing errors and discuss the human-machine interface. Pilots and engineers may also wish to read the human factors resource kits produced by CASA.

Don’t be led astray

Many of us have heard stories about people ending up in the wrong suburb, town or even country because they tried to follow directions from a GPS in their car or mobile phone mapping application.

  • March 2015: A group of Belgian tourists are sent on a detour of close to 1200 km (750 miles) after a GPS navigation error by their bus driver saw them arrive at La Plagne in the Pyrenees rather than La Plagne in the Tarentaise Valley.
  • June 2013: A woman follows her GPS right into the path of an oncoming train in Belmont, US.
  • January 2013: A woman leaves her home in Belgium intending to pick up a friend in Brussels, 144 km (90 miles) away. After switching on her GPS, she ends up in Zagreb, Croatia.
  • March 2012: Japanese tourists drive a rental car into the Pacific Ocean as they follow GPS instructions down a road toward Australia’s North Stradbroke Island.

Pilots have also had accidents to which their GPS units have contributed. Cockpit recordings indicate that a lack of familiarity with the GPS units’ functions, distraction and over-reliance were some of the error-producing influences on the pilots. These potential threats to performance from technology make clear the importance of understanding your strengths and shortcomings, and of the technology you are using.

An awareness of the limitations in the design, controls, displays and software logic of GPS units can avoid potentially dangerous errors such as:

  • incorrect data entries
  • incorrect interpretation of data
  • inadequate cross-checking from alternative sources
  • inappropriate decisions based on GPS output.

Influences on people


A number of factors influence the way that people interact with technology associated with CMS/ATM, such as GPS receivers, ADS-B transponders and cockpit display of traffic information (CDTI) units.

The ‘dirty dozen’ concept, originally designed in the 1990s to improve human performance in maintenance, refers to the most common factors which influence people to make mistakes. In the CNS/ATM context some of the ‘dirty dozen’ provide guidance on how to get the best of from the technology while avoiding the pitfalls.


Most human communication is obtained visually, with 55 per cent from body language, 38 per cent through tone and pitch and only seven per cent the actual words. People normally remember about 20 per cent of what they hear if all they have is sound, which is why aviation radio procedures require readback of essential information such as frequencies, turning instructions and radar codes.

Listening to directions from your GPS tends to be less effective than a passenger giving you the same information, since the passenger provides cues such as tone of voice and possibly gestures.

While technology can reduce pilot workload, the examples above show that interactive systems have limited means of communication with the human interface—so it’s not a matter of ‘set and forget’.

For example, ADS-B surveillance reduces the need for air-ground voice communications for position reports, reducing some pilot and controller workloads. When out of range of an ADS-B ground station, ADS-B IN receiver capability provides the pilot with local airspace information and thus a real time air traffic picture. This additional information should significantly enhance a pilot’s situational awareness.

However, the additional information being presented creates workload for the pilots because it has to be:

  • observed in a timely manner, thus increased scanning
  • interpreted correctly
  • used to contribute to the pilot’s decision-making process.

For example, instead of being instructed to change course or altitude by the ATC, the onus is on the pilots to come to a consensus. And there is an assumption the other aircraft in the vicinity are ADS-B OUT equipped and that the equipment is operating.


Just as using cruise control in a car doesn’t mean that you can travel at a constant speed regardless of other traffic, so there is no such thing as a routine flight. Your GPS may have worked well last time—but what if there’s an in-flight power failure, or it’s a different model this time?

As noted previously, ADS-B assists pilots through providing information, but what if there is more information than the system can provide? An over-reliance on the system to inform may lead to complacency with visual scans. Remember, if you only look for one thing, you may miss important signals because your perception is biased by your expectations and information filtering.

Furthermore, the displays of many GPS units are quite small, with the potential for display reading errors. Warnings such as RAIM are often indicated by small symbols or lights and if the screen is being dimmed by bright light the washout can limit what is actually seen.

A last comment on over-reliance is the old adage ‘use it or lose it’. Drivers in a simulator who follow satellite navigation instructions find it more difficult to work out where they have been than those who use maps. Instructed drivers also fail to notice that they have been led past the same point twice.

Roger McKinlay, the former president of the Royal Institute of Navigation in the UK suggests that our natural sense of navigation diminishes over time if we constantly outsource the responsibility to machines.

And skills need be practised. For example, flight planning and map-reading skills are likely to deteriorate for VFR pilots who routinely rely on the direct-to function on a GPS as their primary means of navigation.

Current knowledge

If dependency increases on ‘outsourced’ knowledge systems, than there is potential for any changes to the systems and procedures to be left to the device to update, rather than on the operator to keep current. The good practice of asking others, rather than assuming the automation is up-to-date, may lapse. To ensure correct procedures are followed, always use checklists and avoid working from memory.

For IFR pilots familiar with ground-based navigation aids, there will be some significant differences in an RNAV environment. These include the display of distance to the next waypoint, cross-track error measured in distance rather than degrees, and absence of slant range. This means that some old rules of thumb and situational awareness techniques may no longer apply. Be absolutely clear about the minimum descent requirements for the approach segment you are in.

A lack of equipment standardisation may cause problems when pilots move between aircraft. For example some CDTIs allow traffic on the ground to be filtered out while others don’t.

An ADS-B OUT interface in the cockpit will not display traffic or terrain, but may let the pilot enter the FLTID.

GNSS units have different modes of operation, including ‘go-to direct’, ‘nav’, ‘waypoint’, ‘alerts’ and ‘system status’, and the function inputs mean different things in different modes. Some equipment does not display the mode, which means pilots need to remember which one they are in.


Distraction is anything which draws a person’s attention away from the task at hand. It’s also the main cause of forgetting things. There is a tendency, when returning to a task after being distracted, to think we are further ahead than we actually are.

Concentrating on only one thing while flying can be dangerous, leading to loss of situational awareness and control. Using interactive equipment can capture your attention for longer than you think.

For example, it’s easy to become fixated trying to find a function hidden deep in the menu structure of a GPS. Familiarise yourself with the technology and do as much preparation as possible, such as entering the waypoints for alternates on the ground to cut the in-flight workload.

GNSS can distract pilots from other tasks, such as monitoring other instruments and scanning for traffic. It can also lull pilots into a false sense of security.


This is particularly, but not only, applicable to multi-crew operations. For example, it’s important to make sure that the information which goes into the GPS and ADS-B units is checked and double-checked, both for accuracy and for common sense. Accidents have happened because crews faithfully input data which was incorrect or ambiguous.


Fatigue is a natural physiological reaction to prolonged physical and/or mental stress. After 17 hours of wakefulness, you are functioning as if you had an equivalent blood alcohol level of 0.05 per cent. After 24 hours the level increases to 0.1 per cent. The more fatigued you are, the lower your cognitive processing speed and memory capacity, which detract from your ability to concentrate and make you more easily distracted.

An area near the front of the brain responsible for logical reasoning and complex thought seems particularly vulnerable to sleep deprivation. This may be why people typically have such a hard time recognising their own fatigue and level of impairment. We tend to underestimate our level of fatigue and overestimate our ability to cope with it. Don’t be pressured into flying if you are fatigued.


Stress can have many causes, and can result in a pilot being less attentive, or making a decision without considering all the information available. It can cause a narrowing of attention, or tunnel vision, making information-gathering (scanning) scattered and poorly organised.

Acute stress from too much work (overload) can be bad for situational awareness. But so can too little stress, or underload.

If a lot of information needs to be prioritised quickly, situational awareness will ultimately suffer. Real-time demands, such as dealing with an in-flight emergency, can cause acute stress to our senses, mental processing and body.

Conversely, during periods of low workload such as in long-haul flying, reduced vigilance may affect your motivation to actively find out what is going on around you. Automation in the cockpit can leave a pilot with little to do, and the lack of stimulation can lead to complacency.

Chronic stress is cumulative, and the result of life events such as family relations, finances, illness, bereavement or divorce can mean our threshold of reaction to demands and pressure at work is lowered. We may over-react inappropriately, too often and too easily.


Norms are unwritten rules or behaviors, dictated and followed by the majority of a group. They can be positive or negative, but most have not been designed to meet all circumstances. Don’t feel pressured into doing something a particular way just because ‘that’s the way it’s done around here’.

The following extracts from reports of occurrences around the world show the potential for human error in the use of GNSS equipment is.

  • ‘Due to a discrepancy between the flight plan stored in the GPS unit and the submitted flight plan, the aircraft tracked via a waypoint that was not on the flight plan.’
  • ‘The accident report of a collision between two aircraft stated that the pilot of one of the aircraft became preoccupied with programming his GPS unit and ran into the other aircraft, the pilot of which was practising ground reference manoeuvres at the time.’
  • ‘The pilot of an aircraft, which was destroyed when it struck trees on departure from an airport, told the investigator that his hand-held GPS receiver had fallen from the instrument panel during the take-off roll and jammed the flight controls.’
  • ‘The pilot was using a GPS receiver to navigate when, about 10 minutes before arrival, the receiver batteries failed. Becoming disoriented, the pilot then used up the remaining fuel trying to locate the airport, eventually making a forced landing into a parking lot.’

Situational awareness

The complexity of aviation operations means that there is potential for even small errors to cause serious problems. A key to avoiding them is to understand the consequences of particular actions.

Safe use of GPS in aviation requires:

  • sound theoretical knowledge
  • operational proficiency with the equipment
  • awareness of both system and human vulnerabilities
  • standardisation of systems and procedures wherever possible.

Ten clues to loss of situational awareness

These clues can warn of an error chain in progress—a series of events that may lead to an accident. Most accidents involving human error include at least four of these clues.

  1. Ambiguity: information from two or more sources that doesn’t agree.
  2. Fixation: focusing on any one thing to the exclusion of everything else.
  3. Confusion: uncertainty about a situation (often accompanied by anxiety or psychological discomfort).
  4. Failure to fly the plane: you are focused on non-flying activities.
  5. Failure to look outside: you are looking down.
  6. Failure to meet an expected checkpoint on flight plan or profile.
  7. Failure to adhere to standard operating procedures.
  8. Failure to comply with limitations, minimums, regulations etc.
  9. Failure to resolve discrepancies: contradictory data or personal conflicts.
  10. Failure to communicate fully and effectively: vague or incomplete statements.

How to maintain and improve situational awareness

Here are some simple tips to help maintain an adequate level of situational awareness in your flying activities.

  • Learn and recognise the symptoms that indicate you are losing situational awareness. For instance, you may be losing situational awareness if you are struggling with GNSS technology in flight, such as flicking through manuals or cycling through control menus.
  • Be well informed. Learn everything you can about the situation. In order to make sound decisions as a pilot, it is vital that you have appropriate and current information available and that it is used as much as is operationally useful.
  • Plan well in advance. ‘Know before you go’ by properly researching flight plans and obtaining the timeliest data possible. Pre-flight planning can start days before a flight and includes knowing everything you can about the aircraft’s capabilities, the weather and the airports at which you will operate.
  • Brief yourself and others on the plan. Take a few minutes to review your flight plan and to brief yourself and your passengers and/or crew on each phase of the upcoming flight. Cover the necessities such as airports, fuel planning, emergencies and anything else that might be useful for that flight.
  • Fly to your plan. Continually monitor the flight’s progress against the original plan that you briefed prior to departure. Always know exactly where you are and be prepared for the tasks that are required next.
  • Use an easily repeatable scanning technique. Make sure that it takes in engine instrument indications, flight instrument indications, aircraft heading, flight path, time, charts and the ground. Develop a scan that covers key items without distracting you too much. The scan should be well-rehearsed and second nature; be careful not to fixate on any one item.
  • Think ahead and rehearse your actions at key points. For example, rehearse your actions should the engine fail in cruise flight, or immediately after take-off.
  • Communicate clearly when operating at, or in the vicinity of, airports. Listen for key words that indicate the positions and intentions of other aircraft. Be aware that not all aircraft will be radio equipped, and even those which are, may not be listening on the appropriate frequency. Think ahead and have a plan for safe and orderly traffic separation.
  • Fly the plane within your limits and the aircraft’s performance limits.
  • Avoid locking on to a problem or task for too long—for instance, your intended landing point. Don’t keep looking only in one direction: keep the scan going, be aware of the relative position and movement of other traffic. Hold the heading and fly at a safe airspeed appropriate to current atmospheric conditions, maintaining your height above the surface.

Cockpit ergonomics

Many aircraft have been fitted with GNSS receivers some years after the aircraft was designed and built. As a result, displays are not necessarily in the ideal location in the cockpit, although IFR installations require the displays to be in the pilot’s field of view. Reflected sunlight can cause problems with both screen displays and annunciator lights and pilots should ensure familiarity with the illumination of the particular receiver installation before night flight.

Many GNSS receivers are coupled to the horizontal situation indicator (HSI) or the primary navigation display. Mode awareness is critical with these installations as different switching and logic arrangements are used to display data from GNSS, VOR, ILS and other sources. Pilots should also be aware of the attentional dominance of the HSI when navigating by a system not displayed on the HSI, and avoid this configuration where possible.

Where does my coffee cup go?

Donald Norman in The Design of Everyday Things (1988, revised 2013)

‘Even the comfort of the flight crew is ignored. Only recently have decent places to hold coffee cups emerged. In older planes, the flight engineer has a small desk for writing and for holding manuals, but the pilots don’t. In modern planes, there are still no places for the pilots to put their charts, their maps, or in some planes, their coffee cups. Where can the crew stretch their legs or do the equivalent of putting the feet up on the desk? And when it is mealtime, how does one eat without risking spilling food and liquids over the cockpit? The lighting and design of the panels seem like an afterthought, so much so that a standard item of equipment for a flight crew is a flashlight.’

Norman says the cramped, inconsiderate design of cockpits is a symptom of a more serious problem. ‘If comfort is ignored, think how badly mental functioning must be treated.

‘Why hasn’t this need been recognised? The need for mental, cognitive assistance should be recognised during the design of the cockpit. Why don’t we build in devices to help the crew? Instead, we force them to improvise, to tape notes here and there, or even to wedge pieces of paper at the desired locations, all to act as memory aids. The crew needs external information, knowledge in the world, to aid them in their tasks. Surely we can develop better aids than empty coffee cups?’

Norman’s proposed solution is user-centred design, meaning it puts the needs of the user before other considerations.

Design should:

  • make it easy to determine what actions are possible at any moment
  • make things visible, including the conceptual model of the system, the alternative actions, and the results of actions
  • make it easy to evaluate the current state of the system
  • follow natural mappings between intentions and the required actions; between actions and the resulting effect; and between the information that is visible and the interpretation of the system state.

Data entry in GNSS units

Both manually entered and database-derived information should be checked for reasonableness with a confidence check in the following cases:

  • prior to each compulsory reporting point
  • prior to or at arrival at each en route waypoint
  • at hourly intervals during area type operations when operating off established routes
  • after insertion of new data; for example, creation or amendment of a flight plan.

Many similar or identical waypoint names exist in a database and it is possible for pilots or software producers to load the wrong waypoint into a sequence inadvertently. Confidence checks should compare tracks and distances against charted information rather than simply scroll through a list of waypoints. Pilots should refer to their company operations manual and to CAO 20.18 for additional information regarding data entry.

Airmanship tips

A lack of mode awareness is a common hazard in computerised flight systems. You must be able to recognise the correct mode of operation for each phase of flight, particularly during instrument approach.

  • Ensure you are familiar with the operating procedures before using the GPS in instrument meteorological conditions (IMC).
  • Check the receiver operation, the database validity and your approach chart before flight.
  • Make sure the receiver is set up with the required navigation settings—distances in nautical miles, QNH in hectopascals etc. Also check the CDI scaling for en route operation.
  • Ensure the GPS is included in your instrument scan but avoid fixating on the receiver.
  • Review the functions of the GPS receiver before each flight by entering the complete flight plan, including the instrument approach procedure to your destination.
  • Do a confidence check of all tracks and distances.
  • As you become more familiar with the unit, guard against complacency, and use all navigation information available to cross-check GPS information.

Key points

  • GPS can deliver gains in reliability, accuracy and system monitoring ability, but training and system familiarity is essential.
  • The lack of standardisation of equipment can cause problems when pilots move between aircraft with different displays.
  • You might lose situational awareness if you are struggling with a GPS in flight, such as flicking through manuals or cycling through controls.
  • The amount of information humans can deal with at any one time is limited and at times, particularly in the IFR environment during high workload phases of flight, it is possible to exceed individual processing capacity.
  • Modern challenges in the human machine interface include cockpit design, which covers how to present information to the pilot; and automation design, covering the question of who should do what, in dividing the task of flying between humans and computers.
  • A lack of mode awareness is a common hazard in computerised flight systems. You must be able to recognise the correct mode of operation for each phase of flight, particularly during instrument approach.


Further reading


  • CASA (2006). A dark side to GPS? Flight Safety Australia, November–December. Retrieved April 2017.
  • CASA (2006). Civil Aviation Advisory Publication 179A-1(1). Navigation using Global Navigation Satellite Systems (GNSS). Canberra.
  • CASA (2006). Overview. Global Navigation Satellite Systems. Canberra.
  • CASA (2006). Instructor notes. Global Navigation Satellite Systems. Canberra.
  • CASA (2014). The error of our ways. Flight Safety Australia, September–October. Retrieved April 2017.
  • Dockrill, P. (2016). Over-Reliance on GPS Could See Us Lose Our Sense of Navigation, Expert Warns, Science Alert. Retrieved April 2017.
  • Harvard University Get Sleep website retrieved April 2017.
Published date: 24 June 2021
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