Sir - I refer to "Why a precision approach is safer" (Letters, Flight International, 17-23 April, P62), in which Dimitris Vourdoubas and Capt John Raby argue the pros and cons of attempting to fly a non-precision approach to a constant slope.
Unfortunately, non-precision approaches vary, not least in that the missed-approach point (MAP) may be an altitude; or a distance, either before or after the navigation aid; a fix at the navaid; at a specified time after thenavaid; or at an intersection or abeam a fix.
As long as all altitude limits are respected and rates of descent sensible, some approaches demand that you get to minimum descent altitude as soon as possible, then fly level to the MAP, thus allowing time for a good look-out - especially if it is necessary to manoeuvre to a non-aligned runway. Other approaches, particularly straight-in ones where the MAP is comfortably before the runway threshold, may better be flown to a constant slope.
Whichever the preferred technique, cockpit workload needs to be reduced by "keep-it-simple" principles and, finally, the pilot must be allowed the flexibility to fly the technique (within reason) with which he or she is most comfortable under prevailing conditions.
GORDON BRETAG
Queensland, Australia
Sir - I would like to clarify part of my letter on precision approaches.
What makes it difficult in bad weather conditions and in reduced visibility to establish a visual reference when a non-precision approach is used is when the attempt is made to convert a non-precision approach to a precision one, by flying a 3¡ path.
An aircraft passing the final approach fix inbound should descend to the minimum descent altitude (MDA) with a higher rate of descent (certainly not with a 3¡ glidepath). This is legal and permits the pilot to maintain level flight until the MAP. The crew then has a better chance to establish visual contact because it flies for longer at the MDA.
It should be clear that an MDA is not a decision height (DH) of the instrument-landing system or precision-approach radar. The DH is the MAP for the precision approach, while the MDA is not.
DIMITRIS VOURDOUBAS
Athens, Greece
Source: Flight International
