What was found
DURING ROUTINE MAINTENANCE AND RECERTIFICATION OF THE AIRCRAFT AIR DATA COMPUTERS AND FLIGHT MANAGEMENT SYSTEM THE TECHNICIANS NOTED THAT THE ADC S SYSTEM HAD BEEN MODIFIED TO USE P/N 7000700-637 ADC S IN PLACE OF THE DEHAVILLAND INSTALLED P/N 7000700-920 UNITS. THERE IS CURRENTLY NO APPROVAL IN PLACE TO USE THE 637 UNITS IN THE DASH 7. A SEARCH OF THE AIRCRAFT MAINTENANCE RECORDS HAS FAILED TO PROVIDE ANY APPROVAL OF THE ADC SYSTEM MODIFICATION OR APPROPRIATE ENGINEERING DOCUMENTS AND CERTIFICATION.