Robert,
I was privileged to have met Dr Pinsker on several occasions where we discussed the differences between open and closed loop landing flare manoeuvres, and thence go-around manoeuvres. He also introduced me to the idea of lift energy, where the wing generates the energy and the tailplane distributes it. Thus, by using more ‘up’ elevator during a go-around, providing more ‘up’ energy, there is less height loss etc, etc.
I flew many of his test points exploring height loss during go-around, these were mainly from 50 ft in support of the Economic Cat 3 Programme at Bedford. I suspect that the ht loss formula used in JAR AWO stemmed from this work, but it may only be relevant to rad alt operations. I think that ground effect was also considered.
There is an example of achieving a new system ‘sub-classification’ in JAR-OPS 1 (sub part E) with the ‘super fail-passive’ autopilot, where an approved system can benefit from lower visibility minima providing operational procedures are modified – GA for any failure. However the method for this approval requires operational demonstration of ‘a highly reliable system’ in service, and only applies to the automatic components of the AWO system. The piloting aspects were covered by existing GA training from 50 ft – no change.
I assume that the benefits sought from the use of modern altimetry would only apply to Cat 1 or NPA approaches.
Where a pressure source is to be used perhaps the largest altitude error will come from the accuracy in setting the datum, which depends on the human’s ability or ‘desire’ (human factors) for accuracy. Geometric altitude (GPS) should not have this problem, but I do not have sufficient details to speculate further. It might be easier to envisage the certification of GPS altitude in the new role if it were already in common use for all altitude tasks. I note that there are quantified reports of significant GPS altitude errors due to external electronic interference.
The current problem of GA altitude loss from MDA (or just above) has been well researched. And even though in some instances a GA from MDA infringes current safety margins (PANS-OPS / TERPS differ) many regulators judge that the benefits of a stabilised, continuous descent with GA at MDA vastly outway the hazards of a ‘dive and drive’ procedure. Thus the benefits (improved safety) come from viewing the overall operation, consisting of the regulations (‘system’ safety), and the operational flight aspects (crew human factors). Such an approach might be required for the altimeter / GA ht loss proposals.
I would be concerned if the arguments for a revision crept into changing more than the altitude component (OCH/A) i.e. “we can go lower, we will be closer, thus we can reduce the visibility”. As with many weather related operations there are few such direct relationships and it should be noted that the ‘transformational’ weather conditions (Cat 2, Cat 1, and NPA instrument to visual transition) often result in situations that require a GA or in which, having made a decision to land, it can subsequently be incorrect.
There are several examples of such regulatory creep i.e. use of certified HUD landing minima for take-off, but the HUD symbols did not enable safe flight with an engine failure during take-off; an engine failed GA was assumed to be a non HUD instrument task (lateral accelerometer). There are similar debates about lowering Cat 2 visibility minima with the removal of the 80% autopilot coupled rule, but the auto / manual flight aspects in this instance are not related.
Dr Sidney Dekker has written an interesting paper on the problem of small changes, gaps, or assumptions made in regulatory methods, see
Past the edge of chaos. A quote from his paper would be good guidance for any regulator, design team, or test pilot:-
“The most important ingredient of engineering a resilient system is constantly testing whether ideas about risk still match with reality; whether the model of operations (and what makes them safe or unsafe) is still up to date. Helios 522 may suggest that we, in Europe, may still be applying models that no longer are.”