I would have expected most Ppruner’s to have learnt by now that the safest method of flying a non precision approach is by using a stable, constant angle approach; then at MDA or the nominated height above, commence a go around if the required visual reference is not achieved.
For the uncommitted then please refer to the Flight Safety Foundation’s ALAR Training Tool Kit and the related CFIT accident examples. Do not forget to use the rad alt …? Yes it can be used as a safety instrument on an NPA. At 10 nm or greater from the airfield the charted procedure should always keep the aircraft above 2500 ft RA. Above 500 ft RA until the final fix, and thereafter always above 250 ft RA until MDA. For those who still duck under; then as soon as your airline fits TAWS; a) the safer we will all be and b) keep you hat ready for visits to the chief’s office to explain those TERRAIN alerts.
I understand that the risk due to height loss depends on which approach construction method is used. Those constructed with TERPS may have slightly more obstacle clearance (higher MDA); thus any loss of height below that is less significant than for approaches constructed with PANSOPS. I also understand that a JAA committee has reviewed a paper assessing the risk of using MDA as ‘DH’ i.e. accepting GA flight below MDA. There appears to be a very small increase in risk such that it could be ignored in comparison with the greatly reduced risk of a CFIT accident when flying CANAPA and using MDA as DH. I guess that any JAA decision will take another 10 committee stages and a year or five to agree yet another compromise.
Some of the most important issues seen in NPA accidents are the lack of planning - calculating required VS and timing, and the failure to use of constant airspeed. Investigations concluded that many crews were unaware of the hazards of making an approach at high constant VS and then decelerating. The effect of the decelerating airspeed without VS adjustment caused the flight path to be well below the expected vertical path; thus the flight path aims short of the runway. This error can be detected by use of alt / dist charts.
I hope that everyone now uses approach charts with tables of altitude vs distance;… and why can’t we have charts with the visual descent point (alt / dist) on them?