The fact that a couple of enhancements to the designs of nonprecision instrument approaches date back to the 1970s should not deter their use whenever feasible as a countermeasure to controlled flight into terrain (CFIT), says Hugh Dibley, a former international airline captain who currently trains Airbus A320 flight crews.
He recently has begun to advocate a well-known mitigation comprising the combination of constant-angle, nonprecision approaches that have distance-measuring equipment (DME) aligned with the final approach course and a standard operating procedure (SOP) that calls for flight crew use of the DME distance–altitude tables on the associated charts to check aircraft altitude at prescribed distances from the runway threshold.
In the early 1970s, British Airways introduced constant-angle descents — beginning at about 7,000 ft over the center of London — into London Heathrow Airport by adding DME navigational aids (transponders) to instrument landing systems (ILS) an…
