The Danish Air Force Home Guard is operating 2 Britten-Norman 2A-21 aircraft. To minimise the noise impact of their operations, exhaust mufflers were installed. Anotec was contracted to obtain the noise certificate for this modification in accordance with ICAO Annex 16, Chapter 10. To this end a flight test campaign was performed at Roskilde airport, where we deployed our mobile flight test lab. Our pilot guidance system was installed in the aircraft to maximise data quality whilst minimising the test time. The test data were analysed with our approved analysis software CEDRA and results reported to EASA. The noise certificate was obtained from EASA a month after the flight tests.