‘Cat A’ conundrum
Thread Starter
Joined: Apr 2019
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From: England
‘Cat A’ conundrum
Dear Fellows,
I am over in Melbourne this week and staying in a hotel right next to the heliport (a small, double pad, pontoon on the river). There is a constant stream of helicopters so I took the opportunity to go and watch for a while. As an aside, if you don’t like helicopters, it probably was not so nice with the noise if you are trying to get a lay-in in the hotel!
Anyway, It was the same handful of aircraft doing the circuit to and from the race course and only one was a twin. The twin stood out as it did a Cat A take-off every time. When I was watching, it was the drop off, so all were empty of passengers on take-off. It made me wonder if the singles would have benefited from such a take-off profile, albeit not within Cat A scope, or if the twin was any safer using that profile when it has redundancy anyway. The Cat A cost a little more time/money to perform compared to the straight up and out profile of the singles.
Any views? Especially if you were one of the pilots involved over these days?
PS, the whole operation looked well managed with plenty of ground crew helping passengers and smooth and consistent approaches (mainly passed my hotel room window at eye level!)
I am over in Melbourne this week and staying in a hotel right next to the heliport (a small, double pad, pontoon on the river). There is a constant stream of helicopters so I took the opportunity to go and watch for a while. As an aside, if you don’t like helicopters, it probably was not so nice with the noise if you are trying to get a lay-in in the hotel!
Anyway, It was the same handful of aircraft doing the circuit to and from the race course and only one was a twin. The twin stood out as it did a Cat A take-off every time. When I was watching, it was the drop off, so all were empty of passengers on take-off. It made me wonder if the singles would have benefited from such a take-off profile, albeit not within Cat A scope, or if the twin was any safer using that profile when it has redundancy anyway. The Cat A cost a little more time/money to perform compared to the straight up and out profile of the singles.
Any views? Especially if you were one of the pilots involved over these days?
PS, the whole operation looked well managed with plenty of ground crew helping passengers and smooth and consistent approaches (mainly passed my hotel room window at eye level!)
Joined: Apr 2012
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From: Down under
As a lowly single engine pilot I'm interested in this also.
How marginal is the single engine performance of big twins machines? Can you always fly at Vy at MTOW with one engine? What about at 30kts?
If it can fly (ROC) at 30 knots with one engine out I can't help thinking a maximum performance style takeoff with an abort point may actually be less risky if anything else failed e.g. tail rotor (aw139 Leicester)
How marginal is the single engine performance of big twins machines? Can you always fly at Vy at MTOW with one engine? What about at 30kts?
If it can fly (ROC) at 30 knots with one engine out I can't help thinking a maximum performance style takeoff with an abort point may actually be less risky if anything else failed e.g. tail rotor (aw139 Leicester)
Joined: Feb 2006
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From: Germany
Hi,
there are quite differences in the case of an engine failure, flying a single or a twin ;-)
So the single engine helicopter pilot has not really many choices.
He needs speed and altitude to carry out an autorotation (ok, to some extend a vertical autorotation is possible)
The twin pilot has options.
If the departure path allows a landing - or transition into OEI (one engine inoperative) flight / fly away, he can choose this departure and saves a few seconds of time.
If in doubt or not possible, the twin pilot will choose the CAT A (or a profile close to it) for departure, regardless of the number of passengers - cause he wants to walk away in case of an engine failure....
Doing so, he would not only walk away but have a functional helicopter (except of that one failed engine).
It needs to get used to it transition from single to twin - but if your instructor has shut down an engine often enough - and you have experienced how stressless it is to land again / fly away at the proper height, you certainly start to see the advantages of a CAT A profile ;-)
there are quite differences in the case of an engine failure, flying a single or a twin ;-)
So the single engine helicopter pilot has not really many choices.
He needs speed and altitude to carry out an autorotation (ok, to some extend a vertical autorotation is possible)
The twin pilot has options.
If the departure path allows a landing - or transition into OEI (one engine inoperative) flight / fly away, he can choose this departure and saves a few seconds of time.
If in doubt or not possible, the twin pilot will choose the CAT A (or a profile close to it) for departure, regardless of the number of passengers - cause he wants to walk away in case of an engine failure....
Doing so, he would not only walk away but have a functional helicopter (except of that one failed engine).
It needs to get used to it transition from single to twin - but if your instructor has shut down an engine often enough - and you have experienced how stressless it is to land again / fly away at the proper height, you certainly start to see the advantages of a CAT A profile ;-)
Joined: Oct 1999
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From: Den Haag
I've had some off-the-books time in an EC135 and it can HOGE OEI at its MTOW,
Joined: Feb 2006
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From: Germany
well, even if all the user I know won’t top up on refueling to stay within limits
the performance OEI isn’t that bad, if you use the 30 sec and/or two minutes power.
And that’s the power you can use on a Cat A departure to either land again (less power required than for hovering) or to transition into flight.
The link in the orher comment, page 61 following
the performance OEI isn’t that bad, if you use the 30 sec and/or two minutes power.
And that’s the power you can use on a Cat A departure to either land again (less power required than for hovering) or to transition into flight.
The link in the orher comment, page 61 following
Joined: Feb 2006
Posts: 927
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From: Germany
the other donk won’t necessarily quit working, if you exceed the times
only instead of changing one - you have then to change two engines and a gearbox 😜
so if you have people hanging below your helicopter- and one engine dies, I‘d rather exceed limits than dropping people to certain death, only to stay within limits...
Best, if proper planning prevents the need to...
Avoid imitations
Joined: Nov 2000
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From: Wandering the FIR and cyberspace often at highly unsociable times
Avoid imitations
Joined: Nov 2000
Aviation Qualifications: ATPL
Posts: 15,110
Likes: 1,083
From: Wandering the FIR and cyberspace often at highly unsociable times
As a long time twin engine pilot, with regard to whether or not to carry out a Cat A departure, I see no reason not to minimise personal risk irrespective of legal requirement, to save a few seconds.
In any case, a smoothly flown Cat A puts less strain on the transmission than does a maximum power pull departure. It also allows me to reject forwards and down visually back to the departure point far more easily than a trying to descend onto it vertically. There might well be reasons other than engine malfunction to reject.
In any case, a smoothly flown Cat A puts less strain on the transmission than does a maximum power pull departure. It also allows me to reject forwards and down visually back to the departure point far more easily than a trying to descend onto it vertically. There might well be reasons other than engine malfunction to reject.
Joined: Dec 2006
Posts: 1,303
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From: UK and MALTA
Have I entered a parallel universe???
Honestly so much rubbish posted on this thread.
CAT A Performance Profiles are hugely varied between the types of helicopters. There are profiles that accelerate almost level. Profiles that go up and backwards/sideways to/from a helipad and profiles that do a whole combination in between. All dependant on the space available and the obstacles around the TLOF.
Each manufacturer publishes a solution based on the engine and rotor performance. There are several different solutions for engine limitations alone.
Trying to explain the difference between a CAT A Departure and a CAT B Departure is really simple:
CAT A - In the event of critical OEI, the helicopter can either: continue the take-off, OR land safely.
CAT B - In the event of critical OEI, a forced landing will be required.
Strain on MGBs and other stuff is irrelevant. If it were there life of the transmission would be curtailed by the number and nature of the CAT Profiles performed.
That's it!
Where's JimL when we need him.
Honestly so much rubbish posted on this thread.
CAT A Performance Profiles are hugely varied between the types of helicopters. There are profiles that accelerate almost level. Profiles that go up and backwards/sideways to/from a helipad and profiles that do a whole combination in between. All dependant on the space available and the obstacles around the TLOF.
Each manufacturer publishes a solution based on the engine and rotor performance. There are several different solutions for engine limitations alone.
Trying to explain the difference between a CAT A Departure and a CAT B Departure is really simple:
CAT A - In the event of critical OEI, the helicopter can either: continue the take-off, OR land safely.
CAT B - In the event of critical OEI, a forced landing will be required.
Strain on MGBs and other stuff is irrelevant. If it were there life of the transmission would be curtailed by the number and nature of the CAT Profiles performed.
That's it!
Where's JimL when we need him.
Joined: Nov 2010
Posts: 35
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From: London
From the T3 RFM Hover Ceiling OGE graph (2 minute power):
Zero wind, bleeds off - MTOM HOGE at 15 degrees C at sea level is 2700kg (2740kg at 30 second power)
From the graph for Max Take-off and Landing Mass for Cat A (VTOL3 profile (Confined helipad)):
Max Mass = 2980 (i.e MTOM) at Sea Level and 26 deg C.
Zero wind, bleeds off - MTOM HOGE at 15 degrees C at sea level is 2700kg (2740kg at 30 second power)
From the graph for Max Take-off and Landing Mass for Cat A (VTOL3 profile (Confined helipad)):
Max Mass = 2980 (i.e MTOM) at Sea Level and 26 deg C.
Last edited by helisniper; 5th November 2019 at 11:57. Reason: Added max mass/alt/temp for Cat A
Joined: Feb 2006
Posts: 927
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From: Germany
Still, the limits for the 30 seconds / two minutes limits, which permit (or not) that a CAT profile is flown are engine and transmission limits.
Newer helicopter actually record the strain of the components - and using much power increases the cycles recorded - and therefore can shorten the time between overhaul.
The original quote about limits was about exceeding them, in case someone dangels underneath and can´t be dropped safely fast enough - which was a litte bit of a thread drift - but no reason to get rude.
best regards
Joined: Jul 2017
Posts: 14
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From: Stockholm
Have I entered a parallel universe???
Honestly so much rubbish posted on this thread.
CAT A Performance Profiles are hugely varied between the types of helicopters. There are profiles that accelerate almost level. Profiles that go up and backwards/sideways to/from a helipad and profiles that do a whole combination in between. All dependant on the space available and the obstacles around the TLOF.
Each manufacturer publishes a solution based on the engine and rotor performance. There are several different solutions for engine limitations alone.
Trying to explain the difference between a CAT A Departure and a CAT B Departure is really simple:
CAT A - In the event of critical OEI, the helicopter can either: continue the take-off, OR land safely.
CAT B - In the event of critical OEI, a forced landing will be required.
Strain on MGBs and other stuff is irrelevant. If it were there life of the transmission would be curtailed by the number and nature of the CAT Profiles performed.
That's it!
Where's JimL when we need him.
Honestly so much rubbish posted on this thread.
CAT A Performance Profiles are hugely varied between the types of helicopters. There are profiles that accelerate almost level. Profiles that go up and backwards/sideways to/from a helipad and profiles that do a whole combination in between. All dependant on the space available and the obstacles around the TLOF.
Each manufacturer publishes a solution based on the engine and rotor performance. There are several different solutions for engine limitations alone.
Trying to explain the difference between a CAT A Departure and a CAT B Departure is really simple:
CAT A - In the event of critical OEI, the helicopter can either: continue the take-off, OR land safely.
CAT B - In the event of critical OEI, a forced landing will be required.
Strain on MGBs and other stuff is irrelevant. If it were there life of the transmission would be curtailed by the number and nature of the CAT Profiles performed.
That's it!
Where's JimL when we need him.
Joined: Jun 2008
Posts: 1,413
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From: England & Scotland
I think the original question was whether singles would benefit from following a Cat A profile departure.
Singles are trying (one would hope) to minimize time in the avoid curve. Their departure profile is therefore going to try to pick up speed at low height then fly away. A Cat A profile would not do that, so I think it would make the single more at risk to follow the Cat A departure profile.
Singles are trying (one would hope) to minimize time in the avoid curve. Their departure profile is therefore going to try to pick up speed at low height then fly away. A Cat A profile would not do that, so I think it would make the single more at risk to follow the Cat A departure profile.
Joined: Dec 2006
Posts: 1,303
Likes: 23
From: UK and MALTA
I think the original question was whether singles would benefit from following a Cat A profile departure.
Singles are trying (one would hope) to minimize time in the avoid curve. Their departure profile is therefore going to try to pick up speed at low height then fly away. A Cat A profile would not do that, so I think it would make the single more at risk to follow the Cat A departure profile.
Singles are trying (one would hope) to minimize time in the avoid curve. Their departure profile is therefore going to try to pick up speed at low height then fly away. A Cat A profile would not do that, so I think it would make the single more at risk to follow the Cat A departure profile.
