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Touchdown and liftoff area (TLOF)Date：8/7/2018 8:12:28 PM
Touchdown and liftoff area (TLOF)
a. TLOF location. TLOFs of general aviation heliports are at ground level, on elevated structures, and at rooftop level. Center the TLOF within the FATO. At a PPR rooftop or other PPR elevated facility, where the entire FATO is not load-bearing, locating the TLOF in a load-bearing area (LBA) that is as large as possible may provide some operational advantages. In this case, locate the TLOF in the center of the LBA.
b. TLOF size. Design the TLOF so the minimum dimension (length, width, or diameter) is at least equal to the RD of the design helicopter (except as noted in (2) below). Design the TLOF to be rectangular or circular. Each has its advantages. A square or rectangular shape provides the pilot with better alignment cues than a circular shape, but a circular TLOF may be more recognizable in an urban environment. Increasing the LBA centered on the TLOF may provide some safety and operational advantages. At PPR facilities, if only a portion of the TLOF is paved, design the TLOF so the minimum
length and width of this paved portion is not less than two times the maximum dimension (length or width) of the undercarriage of the design helicopter. Locate the center of the TLOF in the center of this paved portion. To avoid the risk of catching a skid and the potential for a dynamic rollover, make sure there is no difference in elevation between the paved and unpaved portions of the TLOF.
(1) Elevated public general aviation heliport. If the FATO outside the TLOF is not loadbearing, increase the minimum width, length or diameter of the TLOF to the overall length (D) of the design helicopter.
(2) Elevated PPR heliports. At PPR rooftop or elevated facilities where the height of the TLOF surface above the adjacent ground or structure is no greater than 30 inches (76 cm), and there is a solid adjacent ground or structure equal to the rotor diameter (RD) able to support 20 lbs/sq ft (98 kg/sq m) live load, design the minimum dimension of the TLOF to be at least the smaller of the RD and two times the maximum dimension (length or width) of the undercarriage of the design helicopter. Locate the center of the LBA of the TLOF in the center of the FATO.
(3) Elongated TLOF. An elongated TLOF can provide an increased safety margin and greater operational flexibility. As an option, design an elongated TLOF with a landing position in the center and two takeoff positions, one at either end. Design the landing position to have a minimum length equal to the RD of the design helicopter. If the TLOF is elongated, also provide an elongated FATO. Figure 2–3 shows an elongated TLOF and an elongated FATO.
c. Ground-level TLOF surface characteristics.
(1) Design loads. Design the TLOF and any supporting TLOF structure to be capable of supporting the dynamic loads of the design helicopter.
(2) Paving. Provide either a paved or aggregate-turf surface for the TLOF. Use portland cement concrete (PCC) when feasible for groundlevel facilities. An asphalt surface is less desirable for heliports as it may rut under the wheels or skids of a parked helicopter. This has been a factor in some rollover accidents. Use a broomed or roughened pavement finish to provide a skid-resistant surface for helicopters and non-slippery footing for people. For PPR heliports where only a portion of the TLOF is paved, design the paved portion to dynamic loadbearing. Design the adjacent ground or structure of the TLOF for the static loads of the design helicopter.
d. Rooftop and other elevated TLOFs.
(1) Design loads. Design elevated TLOFs and any TLOF supporting structure to capable of supporting the dynamic loads of the design helicopter. An elevated heliport is illustrated in Figure 2–4.
(2) Elevation. Elevate the TLOF above the level of any obstacle in the FATO and safety area that cannot be removed.
(3) Obstructions. Elevator penthouses, cooling towers, exhaust vents, fresh-air vents, and other raised features can affect heliport operations. Establish control mechanisms to ensure obstruction hazards are not installed after the heliport is operational.
(4) Air quality. Helicopter exhaust can affect building air quality if the heliport is too close to fresh air vents. When designing a building intended to support a helipad, locate fresh air vents accordingly. When adding a heliport to an existing building, relocate fresh air vents if necessary or, if that is not practical, installing charcoal filters or a fresh air intake bypass louver system for HVAC systems may be adequate.
(5) TLOF surface characteristics. Construct rooftop and other elevated heliport TLOFs of metal or concrete (or other materials subject to local building codes). Use a finish for TLOF surfaces that provides a skid-resistant surface for helicopters and non-slippery footing for people.
(6) Safety net. If the platform is elevated 4 feet (1.2 m) or more above its surroundings, Title 29 CFR Part 1910.23, Guarding Floor and Wall Openings and Holes, requires the provision of fall protection. The FAA recommends such protection for all platforms elevated 30 inches (76 cm) or more. However, do not use permanent railings or fences since they would be safety hazards during helicopter operations. As an option, install a safety net meeting state and local regulations but not less than 5 feet (1.5 m) wide. Design the safety net to have a load carrying capability of 25 lbs/sq ft (122 kg/sq m). Make sure the net does not project above the level of the TLOF. Fasten both the inside and outside edges of the safety net to a solid structure. Construct nets of materials that are resistant to environmental effects.
(7) Access to elevated TLOFs. Title 29 CFR Part 1926.34, Means of Egress, requires two separate access points for an elevated structure such as one supporting an elevated TLOF. Title 29 CFR Part 1910.24, Fixed Industrial Stairs applies to stairs. Design handrails required by this regulation to fold down or be removable to below the level of the TLOF so they will not be hazards during helicopter operations.