provide direction and information to taxiing aircraft and airport vehicles. Smaller aerodromes may have few or no signs, relying instead on diagrams and charts. Lighting Many airports have lighting that help guide planes using the runways and taxiways at night or in rain or fog. On runways, green lights indicate the beginning of the runway for landing, while red lights indicate the end of the runway. Runway edge lighting consists of white lights spaced out on both sides of the runway, indicating the edges. Some airports have more complicated lighting on the runways including lights that run down the centerline of the runway and lights that help indicate the approach (an approach lighting system, or ALS). Low-traffic airports may use pilot-controlled lighting to save electricity and staffing costs. Along taxiways, blue lights indicate the taxiway's edge, and some airports have embedded green lights that indicate the centerline. Weather observations Weather observations at the airport are crucial to safe takeoffs and landings. In the US and Canada, the vast majority of airports, large and small, will either have some form of automated airport weather station, whether an AWOS, ASOS, or AWSS, a human observer or a combination of the two. These weather observations, predominantly in the METAR format, are available over the radio, through automatic terminal information service (ATIS), via the ATC or the flight service station. Planes take-off and land into the wind to achieve maximum performance. Because pilots need instantaneous information during landing, a windsock can also be kept in view of the runway. Aviation windsocks are made with lightweight material, withstand strong winds and some are lit up after dark or in foggy weather. Because visibility of windsocks is limited, often multiple glow-orange windsocks are placed on both sides of the runway. Airport ground crew (ground handling) Most airports have groundcrew handling the loading and unloading of passengers, crew, baggage and other services. Some groundcrew are linked to specific airlines operating at the airport. Among the vehicles that serve an airliner on the ground are: A tow tractor to move the aircraft in and out of the berth. A jet bridge (in some airports) or stairs unit to allow passengers to embark and disembark. A ground power unit for supplying electricity. As the engines will be switched off, they will not be generating electricity as they do in flight. A cleaning service. A catering service to deliver food