INSIDE STORY
lowering the nose even though it has. The result may be an increasingly inappropriate control action leading to an excessive nose down attitude, sometimes with fatal consequences. Although a banked aircraft can feel level, a pilot can develop a sensation of flying with one wing low despite the attitude indicator showing straight and level flight — ‘the leans’. It’s a frequent experience for instrument trained pilots manoeuvring in IMC. Occasionally, the sensation can be powerful enough to cause the pilot to mistrust the instruments and it might continue to distract the pilot until there is a clear view of the ground. Figure 2, below, shows the, so-called,
four forces of flight. Newton’s third law states that all forces occur in equal and opposite pairs. Weight is the downward
counterpart generated by the upward lift force on the wings, an increase in lift causes an apparent increase in weight. In flight, weight is not gravity. Too many pilots have died assuming that it is. The lift on the wings gives the pilot a sense of weight and this force feels the same as the effect of gravity when sitting stationary in a chair. But this force isn’t gravity, gravity involves a force directed towards the centre of the earth and which is constant for any given mass. The weight vector that results from
aerodynamic lift on the wings is neither of these things. Both its intensity and its direction are under the control of the pilot. He/she uses the lift force not only to maintain altitude but also to manoeuvre the aircraft. Fore and aft movement of the control column will alter its intensity and a change in the aircraft attitude its direction. Pilots die by assuming that the force they feel is the result of gravity, and therefore earth vertical, when it is not.
Figure 2
DISTRACTION A fully instrument rated helicopter pilot encountered worsening weather over Dartmoor and decided to divert. He pulled up into cloud and started to make radio calls to his revised destination to inform
them of his change of plan. The next thing he noticed, as he described it, was that the cockpit turned green; he had broken cloud and was heading down towards green fields. He was fortunate to have sufficient height to recover and continued, somewhat chastened, to his destination. As he reflected, he could well have
instructed his co-pilot to make the RT call, leaving him to concentrate on flying the aircraft. There would have been nothing about the feel of the aircraft that would have alerted him to his nose-down descent.
INEXPERIENCE Flying the aircraft on instruments involves a considerable increase in workload and inexperienced pilots whose visual flying is approaching the limit of their capacity may be overwhelmed by the requirement for instrument flight if the aircraft inadvertently enters cloud. What’s more, if a pilot has been
attempting to fly on external vision in deteriorating conditions, in the time between switching from the view outside to the instruments the aircraft might have departed from straight and level flight. The consequence of this is that the first glance at the artificial horizon might show an
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