Condicionantes de la intensidad de trabajo

By far the greatest cause of accidents, LOC accounted for 49.7% of the sample and 41.8% of all fatal occurrences. If for any period of time an aircraft performs manoeuvres or movements not explicitly demanded by the pilot, the pilot is deemed to have lost control. In most circumstances, control can easily be regained and there are no adverse consequences. Where no attempt to regain control is made, or recovery is either difficult or not possible, there is a likelihood that an accident will ensue. LOC can be induced by the pilot or by external influences. Within the sample 65.8% of accidents were categorised as pure LOC, 90.6% of which were attributed to HF. More than one quarter (25.5%) of these resulted from the pilot bouncing the aircraft on landing. This can happen for a number of reasons, including poor technique, poor judgment and simple lack of skill. The results of a bounce can be severe if it is not countered effectively, ranging from damaged aircraft to serious injury; the initial LOC (the bounce) may induce further LOC in terms of directional control, or overrunning the runway and collision with vehicles, buildings or other obstacles.

Similar and arguably transferrable from the bounce category, the approach profile of the aircraft was attributable to 24 accidents. The approach profile is the speed, rate of descent and horizontal accuracy of the approach path in relation to the runway centre line. If these are not properly managed, the aircraft can enter a number of undesirable conditions, including excessively high rate of descent resulting in a heavy (and damaging) landing, a stall and/or an undershoot (where the aircraft contacts the ground and/or obstacles before the start of the runway.

Management of the flight and other controls contributed to 45 LOC accidents, all of which occurred during either the take-off or landing phases. Light aircraft are generally sensitive to movements of the controls and thus do not require much physical effort to fly normal manoeuvres. When reacting to external forces such as the wind, it is quite possible to make excessive inputs to the yoke or rudders and subsequently lose control. Similarly, insufficient inputs, particularly at vulnerable times

such as take-off or landing can allow an aircraft to enter a loss of control situation, although this is less common than over control.

For student pilots, high stress situations such as take-off and landing can induce simple mistakes, as they are not yet familiar with the aircraft or the process of operating them. One student with just 20 hours experience (all on the same aircraft type), in an attempt to maintain the aircraft on the runway centre line made a rudder input in the opposite direction to that required, turning the aircraft in the opposite direction from that expected and ultimately lost full control.

In addition to flight controls, inappropriate inputs on other controls such as the throttle or flap levers can also have an unfavourable effect on the controllability of a light aircraft and such events are recorded in the sample data.

Among other contributory causes to LOC, the most notable ones involved overrunning the runway due to poor decision making and/or planning and accidents where condition of the runway resulted in aircraft veering off, landing gear collapsing and ‘nose-overs’ where the aircraft overturns in a longitudinal direction due to the nose wheel either snapping off or digging into soft ground.

Although not so numerous, unsecured aircraft resulted in 16 LOC accidents, usually due to the parking brake not being set whilst starting the engine, or by pilots not noticing their aircraft moving whilst distracted by other tasks such as talking on the radio or performing pre-flight checks. One occurrence however resulted in an un-piloted aircraft taking off and crashing into nearby woods. This extreme case was caused by the pilot not having positioned chocks under the wheels and leaving the throttle in a position so as to elicit an unexpected engine start whilst turning the propeller (some aircraft require the propeller to be turned in order to move oil through the engine prior to starting).

The most lethal form of LOC is that of stalling and/or spinning. Stall recovery techniques are both taught and examined at PPL level, but spinning in the 1990s was removed due to safety concerns, namely that the instruction was causing more accidents than were ultimately being prevented. Whereas a light aircraft is relatively easy to un-stall, (most training aircraft such as the Cessna 152 having a natural tendency to return to controlled flight themselves, given sufficient time and associated height), a spin is more difficult to recover due to the rotation involved, essentially being a condition of stalled flight in which the aircraft enters a spiral descent due to disproportionate amounts of lift being produced by each wing (Thom, 1994). In the sample there were 48 accidents induced by stalling, 10 of which were fatal. Only six accidents were officially categorised as spin occurrences, but all resulted in fatalities. These events took place for a number of reasons ranging

from incorrect configuration of the aircraft through poor techniques in landing or taking off to poor management of speed.

The dual categorisation of LOC and meteorology accounted for 33.2% of accidents, 86.1% of which involved movement of the air; wind gusts, crosswinds, turbulence, down draughts. All but two of these accidents took place on or near the ground in either the take-off or landing phases. Maintaining positive control of the aircraft at these times is crucial as the available time for recovery is severely limited and high levels of awareness and skill would be required to effect a successful recovery.

On take-off or landing, any kind of air movement can put the aircraft into a critical condition in an instant; turbulence or gusting winds can almost instantly starve the aircraft’s wings of the airflow they need to produce lift, thus entering it into a stall requiring a quick response to recover. Similarly, an aircraft can easily be swept across a runway in a crosswind, particularly once airborne and failure to counter this or indeed an excessive motion in an attempt to counter it can lead to LOC. Whilst normal practise is to take-off and land into a head wind, up to specific limits as prescribed by the manufacturer, an aircraft is capable of taking off when the wind is blowing across the runway, but the pilot must use techniques taught in training to keep the aircraft in a straight line. Poor technique or ignoring manufacturer’s recommendations can result in LOC in the aforementioned manner.