@misc{indiciae6e72ccff6b67,
  title = {Slope criteria affecting construction and operation of airports and heliports},
  author = {Rachel M. Barker},
  year = {1976},
  doi = {10.3133/ofr76446},
  url = {https://pubs.usgs.gov/publication/ofr76446},
  note = {Source identifier: ofr76446}
}