Abstract. High-resolution CH₄ and CO₂ measurements were made on board the FAAM BAe-146 UK (Facility for Airborne Atmospheric Measurements, British Aerospace-146) atmospheric research aircraft during a number of field campaigns. The system was based on an infrared spectrometer using the cavity-enhanced absorption spectroscopy technique. Correction functions to convert the mole fractions retrieved from the spectroscopy to dry-air mole fractions were derived using laboratory experiments and over a 3 month period showed good stability. Long-term performance of the system was monitored using WMO (World Meteorological Office) traceable calibration gases. During the first year of operation (29 flights) analysis of the system's in-flight calibrations suggest that its measurements are accurate to 1.28 ppb (1σ repeatability at 1 Hz = 2.48 ppb) for CH₄ and 0.17 ppm (1σ repeatability at 1 Hz = 0.66 ppm) for CO₂. The system was found to be robust, no major motion or altitude dependency could be detected in the measurements. An inter-comparison between whole-air samples that were analysed post-flight for CH₄ and CO₂ by cavity ring-down spectroscopy showed a mean difference between the two techniques of −2.4 ppb (1σ = 2.3 ppb) for CH₄ and −0.22 ppm (1σ = 0.45 ppm) for CO₂. In September 2012, the system was used to sample biomass-burning plumes in Brazil as part of the SAMBBA project (South AMerican Biomass Burning Analysis). From these and simultaneous CO measurements, emission factors for savannah fires were calculated. These were found to be 2.2 ± 0.2 g (kg dry matter)⁻¹ for CH₄ and 1710 ± 171 g (kg dry matter)⁻¹ for CO₂, which are in excellent agreement with previous estimates in the literature.