Introduction

From the initiation of the pre-flight process through the securing of the aircraft at the end of the flight, there are hundreds of decisions to be made and actions to be taken, ranging from weather interpretation, fuel uplift and route of flight selection to the operation of the aircraft and its systems to the navigational aspects of the flight. Proper procedures must be observed and executed to effect the safe completion of the flight and to ensure that no hazard is created to either the aircraft in question or to other aeroplanes in its proximity. Obviously, anything that impairs a pilot's ability to make decisions or execute the associated tasks will increase the potential for an accident or incident.

Discussion

The impairment resulting from the use of some prescription and non-prescription drugs and from the use of alcohol are well documented. As the negative effects of both alcohol and drugs can be exacerbated by the environmental factors of altitude and low humidity found in an aircraft and further affected by circadian cycle, irregular food intake, fatigue or lack of exercise, their effects on pilot performance can be quite profound. National Aviation Authority (NAA) regulations, in general, prohibit the intake of alcohol within the 8 hours prior to flight and some regulators and many companies have extended that prohibition to the period starting 12 hours before reporting for duty or, in some cases, even longer. Likewise, there are numerous regulations prescribing minimum time periods that must be observed between certain medical procedures, anaesthetics and injections and the subsequent return to flying status. Virtually all Company Operations Manuals (COM) will strongly discourage self-medication due to the potential of performance degrading side effects. The effects of alcohol and of some drugs are as follows:

Alcohol

When alcohol is consumed, it is very rapidly absorbed into the blood and tissues of the body but the process of detoxification is quite slow. The impairing effects of alcohol are apparent quite soon after ingestion but it takes about 3 hours for the effects of 1 ounce of alcohol to wear off. Nothing, inclusive of sleep, coffee or exercise, will speed up this process or minimise the effects of the alcohol.

It has been recently determined that alcohol is absorbed into the fluid of the inner ear and will stay there after it has been eliminated from the blood, brain and body tissues. Since the inner ear affects balance, the presence of alcohol within the vestibular apparatus can lead to spatial disorientation and the potential of vertigo.

The presence of alcohol in the blood interferes with the normal absorption of oxygen by the tissues and can result in histotoxic hypoxia. As the reduced cabin pressure at high altitudes has already reduced the ability of the haemoglobin to absorb oxygen (Hypoxic Hypoxia), the effect of alcohol in the blood, during flight at high cabin altitudes, becomes much more pronounced than it would be at sea level. The negative effects of one drink can be magnified as much as 2 to 3 times due to the cumulative effects of alcohol and altitude.

Drugs

Drugs, and the condition or illness for which they are being taken, can negatively impact on pilot performance and efficiency and, as a consequence, can pose a significant risk to safety of flight. Both prescription and non-prescription (over-the-counter) drugs can impair judgement and degrade coordination. Common side effects of many non-prescription drugs, such as cold tablets, cough mixtures, antihistamines, appetite suppressors and laxatives, include drowsiness, confusion, blurred vision and dizziness. The effects of some of these drugs can be even more pronounced at altitude than they are on the ground. Drugs can also have a cumulative effect and, if more than one drug is taken at the same time, the combined negative effect may be well in excess of that of the individual drugs. Likewise, prescription drugs such as antibiotics or antidepressants can have a pronounced affect on judgement, mental acuity and coordination. The advise of a qualified aviation medical practitioner should be sought to ensure that it is safe to fly during the course of a prescribed drug regimen. Obviously, the use of any illicit drug is completely incompatible with flight safety.

• Antihistamines: Antihistamines are often taken to reduce the affects of an allergy or for a specific allergic reaction. They cause a level of sedation with varying degrees (dependant upon both the drug and the individual) of drowsiness, degraded reaction time and disturbances of equilibrium and balance.

• Sulfa Drugs: Sulfa drugs are antimicrobial drugs which inhibit the growth of bacterial. They also cause an allergic reaction in a significant percentage of the population. Side effects of these drugs also can include visual disturbances, dizziness, impaired reaction time, and depression.

• Tranquillisers: Tranquillisers affect reaction time, cause drowsiness, reduced concentration and division of attention.

• Motion Sickness Medications: Motion sickness remedies, in both oral and topical format, can cause drowsiness and depress brain function. They can also result in temporary deterioration in judgement and in decision making skills.

• Weight Loss Drugs: Appetite suppressing drugs inclusive of amphetamines can cause feelings of well being that can affect judgment.

• Barbiturates: Barbiturate, including phenobarbital can noticeably reduce alertness.

Related Articles

• Spatial Disorientation
• Hypoxia
• Prescription

Further Reading

• Drug Use Trends in Aviation: Assessing the Risk of Pilot Impairment, NTSB study on which examines trends in the prevalence of over-the-counter, prescription, and illicit drugs identified by toxicology testing of fatally injured pilots between 1990 and 2012. Published in Sept. 2014.
• FAA AC 120-117: ‘Voluntary Disclosure Reporting Program for Apparent Violations of the Drug and Alcohol Testing Regulations’, December 2017