Night lighting assessment
Very few helicopters are restricted to operations purely during daylight hours therefore assessing the efficiency of the internal lighting arrangement forms an important part of any cockpit evaluation. Illumination is provided in the cockpit to assist the pilot to locate and identify switches and controls in addition to allowing information to be read from cockpit instruments and displays. However it must be remembered that in most tasks the pilot’s primary visual task will involve looking outside the cockpit for external references and the internal lighting should not make this more difficult. The assessment method for night lighting follows the normal cockpit assessment process of conducting a ground evaluation first and then moving on to airborne evaluations. The ground assessment can be conducted using covers to create a fully dark cockpit but further flight assessments under a range of ambient light conditions are essential.
The first task conducted on a night lighting assessment is an evaluation of the illumination of all controls and instruments. Floodlighting often leads to parts of the cockpit being completely in shadow or at best poorly illuminated. Even a small shadow across an instrument can cause problems in extracting information from it. The difficulty of providing balanced and well-controlled illumination can even result in some instruments and controls not being illuminated at all.
The next considerations are control and balance of lighting. With control the designer has to match two opposing requirements. Ideally the pilot would like to be able to control the intensity of illumination for every switch, control and instrument individually to ensure an even balance. On the other hand this would make it difficult and time consuming to switch the lighting on and off and to set the required intensity. The universal solution to this problem is to group lights onto lighting circuits each controlled by a single switch. These groups can be arranged either by cockpit location, such as the complete overhead console, or by function, such as the engine controls. If the balance of lights across a group is not correct it can be problematic; either the brightest instrument can be at the right intensity and the dimmest unreadable or the dimmest readable and the brightest distracting. The balance of lighting is checked to ensure that it is even across individual instruments. The precision with which lights can be controlled is also important as the aircraft will have to be operated in the whole spectrum of environmental light conditions from brightly lit dispersals to near complete darkness. For lights that perform a warning or advisory function it will normally not be advisable to allow the pilot full control over the intensity as it could lead to the light being dimmed to the extent that it cannot be seen.
A major problem with cockpit illumination is unwanted reflections from the variety of internal lighting sources. The position of these reflections is determined and if they cannot be eliminated completely then a judgement is made on the effect they will have during the operational role. External lights such as landing lamps can also create reflection problems. Although not part of a cockpit assessment the effectiveness and control of external lights is usually evaluated during the night lighting assessment.
The provision of lighting during emergencies and following system malfunctions is also assessed. Items such as door jettison handles require luminous markers to be placed on them to provide illumination that is totally independent of the aircraft electrical system. The lighting for critical instruments and displays should not be dependent on the electrical generation system but should be on a busbar supplied directly from an aircraft battery.
The first stage in the testing process is to conduct a failure modes, effects and criticality analysis to determine where problems may lie. The next stage, which is conducted on the ground, is to physically fail or deselect the electrical supply. This is done even if a failure modes analysis indicates that there will be no problem. Following ground tests a carefully planned airborne test is conducted in an incremental manner. The test pilot ensures that the items illuminated and the intensity of illumination are satisfactory for all possible conditions and tasks. During the lighting assessment consideration is also given to engine starting where the power drain on the battery may lead to loss of effective lighting for the engine instruments.
The provision of utility lighting for illuminating piloting documentation such as maps, kneeboards and checklists is also considered. This illumination is usually achieved through ‘wander lamps’ or ‘stalk lights’. Assessment criteria here are controllability, effectiveness and rigidity once adjusted to a position. Checks are made that stalk lights cannot be placed in a position where they could interfere with the flight controls.