Two aviation occurrences in 1999, one of them a fatal mustering
incident and the other a wheels-up landing, highlight some of the
potential hazards of fatigue on flying performance.
Mustering accident
A newly-licensed private pilot was fatally injured at Mindaroo
Station in Western Australia when mustering sheep with a Cessna
172. The accident happened late in the afternoon at the end of more
than eight hours of low-level flying following nine days of intense
flying activity.
During the nine days, the pilot had flown 68 (tachometer) hours.
The flying was both mentally and physically demanding, involving
sheep spotting and low-level mustering.
The pilot, who had no formal low-level or mustering training,
had to manoeuvre the aircraft in conditions that were sometimes
turbulent, and was operating under constant aircraft noise and
vibration. On the day of the incident, he had taken no more than a
short break, which included refuelling after about four hours of
flying.
It is quite possible that he was unaware that fatigue had
affected his flying performance.
The pilot had exceeded the flight duty times normally permitted
for a commercial operation (dealt with in Section 48 of the Civil
Aviation Orders). Although these requirements are not mandatory for
private operations such as this one, they are a guide to flying
limits.
In the absence of any formal duty time requirement, the pilot
was responsible for determining his own daily flying limitations.
This was done in conjunction with the property owners, property
manager and the mustering party. A typical day started at 0700
local time and the pilot worked through the day until just before
last light.
Wheels-up landing incident
In this incident, the pilot of a Cessna 210 had forgotten to
re-engage the landing gear circuit breaker, which had popped during
the flight.
On the morning of the incident, the pilot woke at 0530 local
time and started his tour of duty at 0630. The pilot had flown an
Instrument Flight Rules (IFR) check flight for 2.3 hours in the
morning and his performance was considered to be above average.
The pilot departed on a Visual Flight Rules (VFR) charter
towards the end of the tour of duty. The pilot had pulled the
circuit breaker after it popped to prevent damage to the electric
motor that had continued to run. This procedure was in accordance
with the Cessna 210 Operating Handbook recommendation.
On final approach, the pilot selected the landing gear down but
forgot to re-engage the landing gear circuit breaker and the
landing gear did not deploy. The investigation revealed that the
pilot did not recall hearing the landing gear warning horn nor did
the pilot notice the status of the landing gear indicator
lights.
The investigation concluded that the pilot was probably
suffering from a transient fatigue-related memory lapse and, unlike
the incident at Mindaroo Station, was not suffering severely from
accumulated fatigue. "The pilot reported that he was very tired on
the day of the occurrence and he had been for some time leading up
to the incident," the ATSB report said.
During the investigation, the pilot's work and rest history for
the 14 weeks before the incident was examined using a computerised
fatigue algorithm developed by the Centre for Sleep Research.
The results demonstrated that the pilot probably wasn't
suffering severely from cumulative fatigue. Of more significance
was that the pilot had been on duty for more than 12 hours and had
been awake for almost 14 hours.
Effects of fatigue
Research has shown that the effects of fatigue are similar to
moderate alcohol consumption. On-the-job performance loss for every
hour of wakefulness between 10 and 26 hours is equivalent to a .004
per cent rise in blood alcohol concentration. Eighteen hours of
wakefulness is usually considered to be equivalent to a blood
alcohol concentration of .05. A person who has been awake for this
length of time will act and perform as if they have consumed .05 of
alcohol.
The result is significantly delayed response and reaction times,
impaired reasoning, reduced vigilance and impaired hand-eye
coordination.
The article 'Pilot Fatigue and the Limits of Endurance',
Flight Safety Australia (April 1999), reported that
fatigue makes a pilot less vigilant and more willing to accept
below par performance, and a pilot begins to show signs of poor
judgement. It reported that expert research into fatigue had
established that it degrades a pilot's:
- Muscular strength and coordination
- Vision and perception
- Memory
- Performance monitoring
- Error management
- Decision making
- Motivation and attitudes
- Communication
- Ability to cooperate.
But the greatest single threat is being unaware that it is
happening.
Before the mustering incident at Mindaroo Station, the pilot had
been talking to the ground mustering party by radio as well as
flying the aircraft (possibly below 500 ft). The ATSB investigation
found that he had worked very long hours in a highly demanding job
in which he was inexperienced.
He had received minimal training that would help him to
understand the visual illusions associated with low-level flight.
The investigators considered that in the absence of specific
training for low level flying operations, he was probably unaware
of the appropriate techniques to safely manoeuvre an aircraft at
low level.
According to the ATSB Occurrence Brief (number 199903464) a
human factors report noted that the pilot had worked long hours in
a job in which he was inexperienced and that he probably found this
type of flying both physically and mentally demanding. The report
concluded that at the time of the incident the pilot was suffering
from the effects of fatigue, possibly impairing his ability to
safely operate the aircraft.
According to the Centre for Sleep Research's 1999 report to the
Neville Committee Fatigue and Transportation it has been
difficult for researchers to determine all the factors that cause
and contribute to fatigue; and "determining the relative importance
of these factors under different conditions has also been
problematic".
However, research had concluded that when a person works long
hours, for more than say 50 hours a week, there is increasing
competition between restorative sleep and the other activities of
daily living.
Non-work factors contribute to overall fatigue by a reduction in
the opportunity for sleep and recovery. These include social
factors and domestic arrangements (for example working away from
home) sleep disorders and shift work.
"For example, the same roster could have quite different effects
according to social circumstances," the report stated. "A 12-hour
night shift might have very different consequences for an 18-year
old single male living on his own compared to a 35-year old single
mother of two toddlers without access to 24-hour childcare
facilities.
"Taken together, both employees and employers have clear
responsibilities with respect to managing fatigue. The basic
responsibilities of both parties relate to ensuring that adequate
sleep can be obtained between shifts so that fatigue does not reach
dangerous levels during shifts. Thus, lack of sleep causes fatigue
and sleep allows recovery from fatigue.
"Employers have a duty of care to provide safe work schedules
that permit adequate time for an employee to sleep, rest and
recover as well as fulfil their social and domestic
responsibilities.
"Employees also have a duty of care to use their time away from
work in a safe and responsible mannerto ensure that they obtain
sufficient sleep and recovery in order to complete their work
duties in a safe and responsible manner."
How safe are you?
There are many flying organisations operating with exemptions
from the requirements of CAO 48 issued by the Civil Aviation Safety
Authority (CASA).
Whether you are working to the flight and duty time guidelines
under CAO 48, or under an exemption, how safe are you? Are there
other factors in your life that may make you more tired than
usual?
Remember, the onset of fatigue is insidious.