The CAT A Confusion.....
For years and years there has been confusion as to what CAT A is all about. And I get the feeling that there is still misunderstanding around the terminology.
Very simply [and I will be simple as Nick is watching] CAT A procedures provide you with a set of procedures and flight profiles that are used to ensure/guarantee [as far as the test data can be trusted] that you can safely fly out of a "Departure Point", or safely land back at the same "Departure Point" should you suffer a OEI situation.
As I said earlier, the "Departure Point" can be a Runway, a Ground Level Heliport or an Elevated Platform....and different profiles apply to each one of them.....refer to the CAT A section of your RFM.
The limiting factor of all these "Departure Points" is how much distance there is in front of you to land or to continue.
The most controversial departure is off a runway. There are CAT A Runway Profiles predicated for various aircraft for runway departures....but why would you use it???
The discussion is normally contaminated when using this profile off a runway, because CAT A assumes that there is only a "Definitive" distance to accelerate / OEI /Reject back on distance available. But then it becomes messy because you’re on a huge long runway, so the whole profile now seems a nonsense.
Let’s look at two other Profiles which make a little more sense!!!
Elevated Platform....Remember the aim is to either land back on to the platform or to safety fly away [Not to land on the ground under and in front the platform...but to fly away]. I don't want to talk about specific helicopter types here, but the profile will include a vertical climb, then at a certain height the helicopter will move away from the Elevated Pad and start to fly away...at that point of forward flight the helicopter has reached CDP. Prior to CDP it has the performance to land back on the Elevated Platform and after CDP, it has the performance to achieve Vtoss and climb away.
Remember the definition of Vtoss: In the OEI configation, with the remaining engine set at the 2.5 minute limits, Vtoss is the speed that will ensure the helicopter will climb at 100 Ft/min.
Don't be confused here with International Offshore Standards.....Oil Platform departures are NOT CAT A...there is NO guarantee that you can clear the platform or clear the water if suffering an OEI...unless you are operating to the much reduced weights of CAT A...and then you will soon go broke?? Offshore Ops are not CAT A.
The most restrictive of all the CAT A's is the level Heliport Departure.
Imagine that you have a Heliport totally surrounded by buildings [houses]....Now you have to fly a profile that will ensure/guarantee you will land back on that small heliport if OEI or have the capacity at any stage after CDP to climb over those houses and safety return to home!...crashing is not an option here, you must have the required performance to fly or you can't fly CAT A from this heliport.
Hence you must get yourself in a position to reach Vtoss....this normally involves a vertical and rearward climb to about 100 -130 ft, so you can always see the landing area. At any stage during the climb that you incur a OEI, then the only place your going is back on that heliport.....don't even think about anything else.
OK, now safely at 130 ft or so, then you smartly move the cyclic forward, that point is CDP. Any OEI after that point is an absolute overshoot, you have no other option as you are past CDP. [If you try to land back, the pad will be to close under you and the fence and the first house will be your final resting place].
Once you dive away, normally 15 - 25 degrees nose down, Vtoss will be achieved and you can then be assured of a flight home!!!
There is always talk of CAT A....but really it is a rare event in most pilots lives....CAT B is 99.9% of your life.
I would think the most obvious folk that would use CAT A is EMS chaps going into and coming out of congested inner Suburban Hospital pads.
But at what cost..?? To achieve these CAT A profiles the extra performance must come from somewhere???...that means a reduction in MTOW to enable the profiles to be flown.
Todays aviation world demands us to haul as much payload as possible, so CAT A unless specifically required is very seldom used.
[And talked about to much!!]