aircraft anchored balloon cable checks circular colors colours control controlled duty-pilot engineers fabric filled flight-operation gondola height helium helium-balloon high inspected inspections large limited mesh metal-cable metal-line monitored monitoring motion movement net passengers pilot piloted registered ride safe safety secure secured sights sightseeing Singapore tethered tourists views weather-limits wind-limits autumn backdrop background calm cirrus cloud clouds cloudy cosmos cumulus dreamy ecological ecology fluffy formation formations free freedon heaven heavens horizon light limit limits meteorology mood natural nature nimbus outdoor panorama peace peaceful rain restriction restrictions road sign skies sky space speed speeding spring storm strato-cumulus stratus street summer sunlight sunlit sunny texture tranquil tranquility unrestricted wallpaper weather weirdvis winter