Well-designed systems require a certain measure of redundancy if they are to function acceptably during occurrences of partial failure or abnormality.
In the National Airspace System (NAS) of the United States, there currently exists a dangerous and unacceptable lack of redundancy: the inability of flightcrews operating under radar control in instrument meteorological conditions (IMC) and according to instrument flight rules (IFR) to verify the propriety of radar vector assignments issued to them by groundbased air traffic controllers.
The problem has three dimensions: (1) the criteria used by the FAA in the formulation of minimum vectoring altitudes (MVAs) are different from, and generally more permissive than, those used in the determination of the “minimum” IFR altitudes portrayed on aeronautical charts used by pilots; (2) pilots operating in (IMC) are routinely directed away from published routes to which the charted minimum IFR altitudes apply; and (3) pilots presently have no accurate, independent, and timely inflight method of efficiently determining the MVAs applicable to their particular flight path, so many attempt to substitute other procedurally derived (but operationally inapplicable) altitudes in lieu of proper MVA information.
The practice of substituting inappropriate minimum altitude information for applicable MVAs will be examined, along with the writer's suggestion that the FAA's planned Hode-S Beacon System be evaluated as a candidate medium for providing timely, cost-effective, and off-published-route MVA information to pilots of all types of aircraft.