What is Category A?

[crop duster]

Flying cropdusters we don't have much need for IFR except maybe ( I Follow Roads) so for those of us that would like to know but are afraid to ask, what are the requirements for Category A?
Barryb :confused:

[MightyGem]

In the UK it's the ability of a twin engined helicopter to be able to continue to climb, above a set rate to avoid obstacles, if an engine fails just after take off. There is probably a requirement for it to be able to maintain level flight if it loses one in the cruise, but I'm not sure on that.

[Nick Lappos]

Cat A is refered to in FAR Part 29 (Airline Transport Rotorcraft) and is a set of design and performance standards to assure safety. It involves a set of procedures and the charts to go with them to assure that anywhere along the flight path a prescribed climb capability exists after a critical Decision Point on takeoff, and before a Landing Decision Point on approach. Before the CDP and after the LDP, the procedures describe what the heliport dimensions must be, and what the obstruction clearance capabilities are.

True Cat A is not required in any operations in the US and few in the world, but many Ops requirements call for "Enroute Cat A" which means that they accept the inability to make a successful climb away during the few seconds it takes to get to climb speed on takeoff, but demand that the hours spent in cruise allow single engine cruise capability. Most helicopter airlines in the world operate as Air Taxi (Part 135), not as Airline (Part 127) because the FAA recognizes the economic burden of hard Cat A vice the tiny probability of engine malfunction causing a flight mishap.

The real issue is that Cat A from low speed requires vastly reduced payload for today's helicopters, and much larger engines for helicopters specially designed for it. For example, the S-92 is hard Cat A from hover to hover, the S-61 is not at all like that. The S-92 has two engines at 2500 Hp each, the S-61 has two at 1400 Hp.

Cat A requires clearance of a hypothetical 35 foot barrier, climb rate of at least 100 fpm until Vy, then maintaining at least 150 feet per minute climb 1000 feet above the heliport and anywhere enroute.

The design requirements have lots of stuff about separation of the engines (so one quitting doesn't jeopardize the other), as well as fire zone integrity (so you can have a "High and Mighty" type fire and keep flying.)

Old BCAR had a similar set of requirements called "Group A" which were similar in intent, if not detail.

[B Sousa]

In The World of Crop Dusting, Category A would be you flying from Bubbas Ranch over to a sourgum filed to spray. You would recognize the field by the color of the mud kicked up when your wheels skipped along. You would only be able to see the flagman from 1200 feet and would also be so low that you would only see him when he dove into a ditch to avoid you hitting him. He would be further confused as you are flying a Biplane and he could only see one wing as the upper is in the clouds....
Upon return you could tell where you had been by the types of wires wrapped around the main gear and Old Maudes phone line off the tail wheel
Thats sort of Cat A....

[SASless]

Nick,

Fingers crossed here.....what kind of performance can we expect out of the S-92 for a ship pilot hoist op at +45 C day? Maintain Hover and depart OEI with 1.5 hours fuel aboard and 6 pax plus crew after an engine failure??? Is that how far technology has gotten us?

Is not the answer here....to build helicopters with sufficient power margins that allow reasonable performance on one engine to allow for specialized ops that are becoming more prevalent as time goes on....Pilot hoists, SAR hover recscues,high rise fire rescues (WTC type disasters?), mountain rescues?

[Nick Lappos]

Sasless,

That is exactly what we exchanged thoughts over in the other thread. You lament that new missions threaten us, and demand OEI capability in those missions, but you do not demand OEI SAFETY!

While we can do a dynamic maneuver by using a blend of technologies, the raw power to simply hover OEI is not yet possible without major tradeoffs. I doubt that even a three engined helo can meet your requirements.

I won't repeat all the stuff from the other post, just jump to the bottom line:

What is so magic about an engine failure? Why do you not demand that we withstand a bounce off the water, since that is the prevelant cause of accidents? Have you looked at the data from the OGP report?

[TeeS]

Nick

your mention of three engine helicopters brought to mind a conversation many years ago when the EH101 was first being talked about. One of the pilots made the ('I think') valid point that we make so much fuss about cat 'a' performance, yet the North Sea had never to our knowledge had a performance related accident. However we had just gone through a rash of gearboxes falling apart at their input shafts. It appeared to us that the only effect of adding a third engine was to increase the possibility of an aircraft ditching by 50%.

[Nick Lappos]

TeeS,

Since I am the Program Manager of the S-92, I should jump up and agree with your post!

But, in all honesty, the third engine was put in the EH because it grew big enough to need the total horsepower, but there was no pair of engines big enough to fit the bill. We had the same choice with the 53E when we grew it from the 53D.


Nick