AW139 Cat. "A" and Cat. "B" discussion

[Geoffersincornwall]

Outwest et al

From a practical point of view there has to be something other than a Cat A procedure for take off and landing for it is simply not possible for all types of operations to comply with it's rigid protocols. This observation is especially poignant when the RFM emphasises that any deviation from the profiles defined in Supplement 12 etc. will render the performance data inapplicable. What constitutes a 'deviation'? Ten knots? five? twenty feet? ten? Very tricky to teach when you have that degree of inflexibility.

For those non Cat A operations (i.e.. the majority) they must do the best they can to manage the risks of operating from ad hoc sites (HEMS, POLICE, SAR, Corporate, VIP, VVIP, Private). Of course it would be handy if you could use the published Cat B profile but that was developed (or so I understand) in order to deliver the certification requirement (to state the distances required to land and take off over a fifty foot obstacle).

I suggest that it cannot be the case that no other take off or landing profile is permitted, if that were the case then we have a problem. The reality is that you do what you have to do and minimise the exposure to an engine failure. The AW139 has to be one of the best, if not THE best medium machine in that respect.

Teaching Cat B in the sim (and we are assured that the sim's performance mirrors the real aircraft) I can demonstrate that in the event of an engine failure during take off it's possible to bring ground speed back to zero or close to it at weights up to 6400 and thereby cope with poor terrain with minimum damage to the airframe.

The emphasis of Cat A is on climb performance whereas Cat B - or maybe I should call them 'non-Cat A' profiles - do not necessarily require a climb capability as long as you can see and avoid the obstacles.

So from my viewpoint it would be OK to say that a Cat B take off is anything that is not Cat A. In other words it is a profile that comes with no performance guarantees. Mr Baggi is an expert on the certification process and I bow to his knowledge and expertise in this respect but the operating world is much much bigger than that defined by the certification criteria. Maybe it will be necessary to have another way of describing profiles that are operationally essential but unable to fit those described by the certification process or we simply call the PC2 or PC3.

There are many out there who will use a familiar profile but are unable (or unwilling) to comply with the mass requirements or unable to quantify the obstacle environment with the accuracy required by the Cat A protocols. There are also those that do use a Cat A profile AND observe the mass limitations but due to operational constraints also have the problem of quantifying the obstacle environment. This is common when using ad hoc operating sites. None of these can be described as Cat A Operations and so they are unlikely to be PC1 compliant either.

G.