Human Performance and Limitations - Complete Summary
Table of Contents
The shel model
The gas laws
The Human Body
Nervous and endocrine systems
Central nervous system
Body temperature control
Spatial disorientation and illusions
Constant angle col isions
Health problems in aviation
Problems influencing a pilot
Tropical and epidemic diseases
Memory, learning and acquiring skills
James Reason’s model
Strategies for coping with human error
Flight deck ergonomics
70% of al the accidents are attributed to human errors. Many accidents are not caused by a
single factor only.
Human error can also be made by engineers/managers etc. on the ground. It’s not always the
pilot his fault.
Before training, the number of faults made by a human is 1:100. So, 1 fault in every 100 actions.
After training, this ratio can be brought back to 1:1000.
The shell model
The shel model is a model that lets liveware (people), relate to other
- Software. Someone reading a manual/ checklist.
- Hardware. Using switches/ controls in a plane.
- Environment. Weather conditions.
- Liveware (other people). ATC communications.
There are at least two ways of treating a safety culture:
- What the organisation thinks (attitude of employees towards safety).
- What the organisation does (procedures/ protection etc.).
ICAO tries to set up international safety standards, since there are big differences between
countries. To do so, they publish Standard and Recommended Practices (SARP’s).
This leads to an open culture: people report incidents freely to improve flight safety and learn from
previous accidents and incidents.
Swiss Cheese Model: sometimes, even with many safety barriers, an accident happens because
all borders are passed.
Dr. Reason thinks that a safety culture consists out of 5 elements:
- An informed culture. Organisation collects and analyses relevant data, and actively
disseminates safety information.
- A reporting culture. Cultivating an atmosphere where people have the confidence to
report safety concerns without fear of blame.
- A learning culture. Organisation is able to learn from its mistakes and make changes.
- A just culture. Unsafe acts will not be punished if the error was unintentional.
- A flexible culture. Organisation and the people in it are capable of adapting effectively to
SMS stands for a Safety Management System.
TEM stands for a Threat and Error Management. Difference:
- Threats: events/ errors that occur beyond the influence of an operational person.
- Error: action/ inaction by an operational person that leads to deviations from the
organisational/ operational intentions and expectations.
The atmospheric conditions are always compared to standards. This standard is called ISA, which
stands for International Standard Atmosphere. There are different standards at different heights:
The gas laws
There are multiple laws that describe how the volume, pressure and temperature of a gas can
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As pressure increases, volume decreases.
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As temperature increases, volume increases, if pressure remains constant.
Sum of the partial pressures gives the total pressure. So: 21% oxygen is responsible for 21% of
the total pressure.
Gas diffuses from high to low concentration areas.
States that the amount of gas dissolved in a liquid is proportional to the pressure of that gas over
General gas law
This law relates to both Boyle’s and Charles’ laws.
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The Human Body
inhaling and exhaling to transfer O2 to the blood
and CO2 to the air. When exhaling, the
intercostal muscles relax. Breathing can be
referred to as external respiration.
One cel -layer thick: here the O2 <->CO2 process
takes place. Gas transfer.
- Total capacity of 6000mL.
- Tidal volume of 500mL.
- Residual volume of 1000mL.
- Vital capacity of 5000mL.
Vital capacity is the difference between the capacity of the
lungs after maximum inhalation, and the capacity remaining
after maximum exhalation.
Residual volume is the volume remaining after maximum
Inspiratory capacity is made up of the resting tidal volume (air going in and out of the lungs
during normal respiration) and the inspiratory reserve volume (extra air being inhaled when
working out, when the body requires more oxygen).
Expiratory reserve volume is the volume of air in the lungs when the body is at rest, and normal
expiration has occurred. This comprises of the expiratory reserve volume and the residual
Haemoglobin is used to transfer O2, via red blood cells, through the body. CO2 dissolves in the blood
The rate of breathing depends on both O2 and CO2 concentrations. CO2 is more significant. Rising
CO2-concentration therefore means that it leads to a higher breathing rate, to restore the optimum
ratio between CO2 and O2.
CO is a toxic gas. The body ‘thinks’ you’re breathing in O2, but actual y gets tricked by the similar
looking CO-gas. When facing during flight:
- Put on oxygen masks.
- Switch off cabin heating.
- Open fresh air vents.
- Avoid smoking.
- Maybe land ASAP.
shown in red. Carry oxygenated blood from the heart
to the body tissues. Exception: pulmonary artery
(heart to lungs, unoxygenated).
shown in blue. Carry unoxygenated blood from the
body to the heart. Exception: pulmonary vein (lungs
to the heart, oxygenated).
main artery from heart to the rest of the body. Heart
itself is supplied with oxygenated blood via the coronary arteries.
Heartbeat: right ventricle à lungs à left atrium à left ventricle à
- 72 bpm in rest
- 70ml blood per beat
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Normal, typical blood-pressure is 120/80. Depends on:
- Work of the heart.
- Peripheral resistance.
- Elasticity of arterial walls.
- Blood volume and viscocity.
caused by reduction in the amount of haemoglobin available.
Hypoxia is the shortage of oxygen. In a normal situation, 21% of the air at sea level is oxygen (O2),
from where there is 14,5% in the lungs. It does not lead to shortage of breath, since there is no
excess of carbon dioxide.
The external pressure changes are greatest at low level. At sea level, 103mm Hg shows the
partial pressure of oxygen at sea level.
There are a few stages described in order to show what a shortage of oxygen does to our body.
This is important since modern airliners are operating at high altitudes with low concentrations
1. Indifferent stage.
0ft – 10.000ft with a saturation of 98% - 87%.
2. Compensatory stage.
10.000ft – 15.000ft with a saturation of 87% -
3. Disturbance stage.
15.000ft – 20.000ft with a saturation of 80% -
4. Critical stage.
20.000ft – 23.000ft with a saturation of 65% - 60%.
100% oxygen is needed between 33.700ft and 40.000ft. Above 40.000ft, 100% oxygen under
pressure must be used.