2.3.4.2. Logo lights
Referring to Fig. 11, logo lights are used to illuminate the tail fin; this is primarily for promotional purposes, i.e. for the airline to highlight their logo during night operations at an airport. Apart from the advertising value at airports, they are often used for additional awareness in busy airspace. Taxi lights (or runway turn off lights) are sealed beam devices with 250 W filament lamps located on the nose, landing gear or wing roots. They are sometimes combined with the landing light and used when approaching or leaving the runway. Taxi lights improve visibility during ground operations; they are directed at higher angle than landing lights. Runway turnoff lights, in the wing roots, are normally only used at night on poorly lit runways. A typical fixed landing and taxi light circuit is shown in Fig. 12. On some aircraft types, taxi lights will switch off automatically with gear retraction. It is common practice to have taxi lights on whilst the aircraft is in motion as a warning to other aircraft and vehicles.
Figure 11 Exterior lights (turn off/logo)
Figure 12 Fixed landing light circuit
2.3.4.3. Landing lights
Landing lights are located on the wing tips, or on the front of the fuselage, usually at fixed angles to illuminate the runway. They are sealed beam devices with 600-1000W filament lamps; a parabolic reflector concentrates light into a directional beam. The high current requirement is controlled via a relay. Some landing light installations have a retractable assembly located on the underside of the wing. This has a reversible motor and gear mechanism to drive the light out against the airflow; a typical circuit is illustrated in Fig. 13. The alternative location for a landing light is in the wing leading edge; this has a transparent cover to provide aerodynamic fairing. Inboard and outboard landing lights (Fig. 14) provide extended illumination of the landing area.
2.3.4.4. Wing illumination
Ice inspection lights (Fig. 14) are often installed to check ice formation on wing leading edges and engine intakes. Typical lights are the sealed beam type with filament lamps of 50-250 watts. They are recessed into the fuselage or engine nacelle with a preset direction that illuminates a section of the wing that can be viewed from the flight compartment.
Figure 13 Retractable landing/taxi light circuit
Figure 14 Exterior lights (landing/wing)
2.3.4.5. Service lights
Service lights are provided throughout the aircraft as illustrated in Fig. 15. These lights are powered from the aircraft ground servicing bus. Examples include:
• cargo bays
• wheel wells
• equipment bays
• fuelling panels.
Wheel wells lights are normally only used during the turnaround at night during the pre-flight inspection; they can also be used on to see the mechanical gear down-lock indications at night.
Figure 15 Exterior lights (servicing)
2.3.4.6. Navigation lights
The primary external lights required for navigation purposes are the beacons and anti-collision lights, see Fig. 16.
Figure 16 Exterior lights (beacons/strobes)
The navigation (or position) lights are a legal requirement for night flying. Navigation lights are normally based on filament lamps, providing steady illumination. They are located at the extremes of the aircraft, see Fig. 17, and provide an indication of the aircraft's direction and manoeuvres. Navigation lights are based on regulations that define the colour, location and beam divergence such that the aircraft is visible from any viewing angle; these colours and divergence angles are:
• green, starboard wing, divergence of 110 degrees
• red, port wing, divergence of 110 degrees
• clear (white), tail, divergence of ±70 degrees either side of aircraft centreline (140 degrees total).
Figure 17 Navigation lights - angular coverage
The traditional location of the white light is on the tail cone or fin tip; some aircraft have the rear facing light on the trailing edge of each wing tip. The wing lamps are 20 W filament lamps, the tail lamp is 10 W. Coloured filters produce the specific colours; these filters must not shrink, fade or become opaque. A typical navigation light circuit is shown in Fig. 18. Note that the lights are controlled by single switch and protection device.
Figure 18 Navigation light circuit
Some aircraft are installed with LED position lights; these are formed with a bank of LEDs, see Fig. 19. Helicopters have varying navigation light installations due to their specific geometry, see Fig. 20.
Figure 19 Position lights: (a) LED type; (b) wing tip location
Figure 20 Helicopter lights: Twin landing lights on nose; Navigation light below door; Additional landing light on rear skid
Anti-collision lights often supplement navigation lights; these can be provided either by a strobe light, rotating beacon or a combination of both, see Fig. 21. Anti-collision lights are also used as a warning that the engines are running or are about to be started. They are typically not switched off until it is considered safe for ground personnel to approach the aircraft. Strobe lights are typically located on the:
• vertical stabilizer
• wing tips
• tail/lower wing surfaces
• fuselage.
Figure 21 Anti-collision strobe lights
These anti-collision lights are controlled by a single switch, with a single protection device. Anti-collision lights used in conjunction with the navigation lights enhance situational awareness for pilots in nearby aircraft, especially during night-time or in low-visibility conditions.
The rotating beacon comprises a filament lamp, reflector, motor and drive mechanism that gives the effect of a light through a red filter that flashes 40-50 times per second. A typical rotating beacon is illustrated in Fig. 22. They are located on tail fins and the upper and lower fuselage (or tail boom on a helicopter).
Figure 22 Rotating beacon (top of fin)
Strobe lights are wing-tip and tail-fin mounted to supplement navigation lights. The strobe light produces a high intensity white flash of 1 mS duration at approximately 70 flashes per minute through a white or red filter; these provide light that can be seen from several miles.
Many external lights are based on sealed beams. A sealed beam combines an incandescent filament lamp and reflector into a single assembly. The reflector concentrates the light from the lamp into a predetermined beam shape; the assembly is fitted with a clear glass front cover that is permanently sealed to the reflector and cannot be removed. The filament lamp is inserted through a hole in the rear of the reflector and retained by a locking mechanism.