The GDC22 Data Converter received ARINC 429 and GAMA 429 labels from a Garmin model GPS400, modifies the content of label 116, creates label 270 from the data contained in label 275G and stores labels 001, 012, 114, 314 and 321 for transmission. It discards all other received labels. The GDC22 then transmits the modified and unmodified data in ARINC 429 format for use by a Thales HSI.