High resolution infrared spectroscopy is a very useful technique for remote sensing of atmospheric constituents. From an aircraft it is possible to use emission or absorption spectroscopy to measure total quantities of constituents above the aircraft or profiles at altitudes below the flight. The adaptation of a commercial high resolution (0.06 cm-1) Fourier transform infrared spectrometer for use in absorption spectroscopy on a jet aircraft is described, emphasizing methods of dealing with the difficulties of the aircraft environment. Atmospheric constituents with concentrations less than one part per billion can be measured.