In 1963, GATC introduced the 4180 Cubic Foot Airslide covered hopper to their product line. Designed for shippers of such commodities as flour, starch, and sugar, these two-bay cars featured ten round loading hatches and four outlets. As with their other Airslide designs, it featured their patented ‘Airslide’ unloading system which uses pressurized air to aerate the special fabric lining of the bays, effectively fluidizing the commodity and allowing it to flow more easily during unloading.
As with most any locomotive or rolling stock, the 4180cf Airslides underwent production changes over their production span. These changes were typically the result of improvements in fabrication, changes in railroad regulations, and/or changes in vendor components. This evolution is unofficially termed as ‘phases’ by railroad enthusiasts. Per noted freight car historian Eric Neubauer’s definitive work on Airslide covered hoppers, 4180cf Airslide production broke down as follows:
Phase ‘HAT’ – These Airslides featured full-height ladders at the side corners, hat-section side posts, high handbrakes, and “Z” section horizontal end braces, and wire-loop roping eyes. Built from 2/63 – 5/64.
Phase ‘TZH’ – This evolution to the 4180cf design was similar to the previous HAT cars, but with a change to the truck centers, and a change to bolster jacking plates with integral roping eyes, in place of the wire loops. Built from 6/65 – 3/66.
Phase ‘TZL’ – Outwardly identical to Phase ‘TZH’ cars, these Airslides featured low-mounted handbrakes and half-height ladder grabs at the side corners, to comply with changes to freight car appliance regulations. Built from 9/66 – 1/69.
Phase ‘TZC’ – This phase introduced notable changes to the 4180cf design, mainly the change of the side posts, except those at the bolsters, to a fabricated square-column style. The posts at the bolsters remained ‘hat-section’, as on previous production. This phase was produced during the first half of 1966.
Phase ‘HZ’ – This phase progression from Phase TZC saw the posts at the bolsters change from hat-section posts, to I-beam style posts. Produced for a brief period from 8/69 to 1/70.
Phase ‘HC’ – The final 4180cf Airslide variant, this version featured square tube-style horizontal end braces, in place of the Z-style of previous versions. They were produced from 10/70 until 10/80.
Production of the 4180cf Airslide would continue until 1980 when it was superseded by the larger 4566cf Airslide design. Most continued in service into the 2000s. Age and obsolescence thanks to larger Airslides and newer Pressure-Differential designs have slowly thinned their ranks. BNSF has repurposed several 4180cf Airslide Covered Hoppers for buffer car service so they continue in operation today.