The word helipad is a portmanteau meaning helicopter landing pad, a landing area for helicopters. Though helicopters can usually land anywhere flat, a fabricated helipad provides a clearly marked hard surface away from obstacles where a helicopter can land. Helipads are usually constructed out of concrete and are marked with a circle and/or a letter "H", so as to be visible from the air. They may be located at a heliport or airport where fuel, air traffic control, and service facilities for aircraft are available. Usually a helipad does not have fuel and service facilities for aircraft, as does a heliport, and does not maintain a full time air traffic controller. Conversely, a helipad may also be located away from such facilities; for example, helipads are commonly placed on the roof of hospitals to facilitate MEDEVACs. Large ships sometimes have a helipad onboard, and some businesses maintain a helipad on the roof of their office tower. Helipads are not always constructed out of concrete; sometimes forest fire fighters will construct a temporary helipad out of wood to receive supplies in remote areas. Landing pads may also be constructed in extreme conditions like on frozen ice. The world's highest helipad, built by India, is located in the Siachen Glacier at a height of 21,000 feet above the sea level. Rooftop helipads sometimes display a large two-digit number, representing the weight limit (in thousands of pounds) of the pad.
