Category A Takeoff: Background
Ok .. I still see more negatives from backing up than positives so don’t ever do them myself. I get the point that if it’s in the manual you do it ..... just wonder how they came to that conclusion!!!
With respect to performance, the main point of a Category A procedure is to provide engine-failure accountability.
With an engine-failure anywhere in the profile, the pilot should be able to return to the take-off point or continue the flight safely (avoiding all obstacles) to a place where a landing can be carried out - all without damage to the helicopter.
For a helipad departure:
Category A is a certification standard which provides assurance of continued flight in the event of a failure by employing design assessment, to reduce the probability of failure. Engine isolation ensures that one engine failure is unlikely to lead to a second, and fire in an engine compartment can be detected, contained and/or extinguished. These provisions give a level of confidence that the helicopter can be operated for continuous periods over a hostile environment.
Category A requires performance data so that One Engine Inoperative (OEI) obstacle clearance from take-off, through climb, cruise and landing can be calculated. This data should include: mass related take-off and landing procedures; heliport/helideck size limitations; distances and climb gradients (or rates of climb); and one-engine inoperative climb performance graphs. From these procedures and graphs an operator/pilot can establish an OEI flight trajectory.
The failure rates for engines and tail-rotors (should) differ by four orders of magnitude. When reliability of any system does not reach the desired level it is mitigated by the provision of redundancy (in this case two engines).
JimL
With an engine-failure anywhere in the profile, the pilot should be able to return to the take-off point or continue the flight safely (avoiding all obstacles) to a place where a landing can be carried out - all without damage to the helicopter.
For a helipad departure:
- at any point up to the TDP and following an engine-failure, the pilot must be able to return to the take-off point and land the helicopter safely. That means that the pilot has to have sufficient visual cues to be able to conduct the landing, and the helicopter sufficient power to allow a controlled descent and landing.
- from the TDP and following an engine-failure, the pilot must be able to clear all obstacles by a safe margin, climb and continue to the flight to a point where a safe OEI landing can be carried out.
Category A is a certification standard which provides assurance of continued flight in the event of a failure by employing design assessment, to reduce the probability of failure. Engine isolation ensures that one engine failure is unlikely to lead to a second, and fire in an engine compartment can be detected, contained and/or extinguished. These provisions give a level of confidence that the helicopter can be operated for continuous periods over a hostile environment.
Category A requires performance data so that One Engine Inoperative (OEI) obstacle clearance from take-off, through climb, cruise and landing can be calculated. This data should include: mass related take-off and landing procedures; heliport/helideck size limitations; distances and climb gradients (or rates of climb); and one-engine inoperative climb performance graphs. From these procedures and graphs an operator/pilot can establish an OEI flight trajectory.
The failure rates for engines and tail-rotors (should) differ by four orders of magnitude. When reliability of any system does not reach the desired level it is mitigated by the provision of redundancy (in this case two engines).
JimL
The vertical procedure is more easily reproducible - vertical climb to a radalt height using a given vertical speed ensures consistency and works well for elevated pads where going backwards will invalidate a radalt reading. However, there are greater performance constraints due to zero airspeed and it is easier to lose sight of the reject area (also leading to a lower usable TDP).
The Back-up technique allows a higher TDP and brings performance benefits due to being able to acquire airspeed from the higher reject heights. However, there will be greater variability in how it is flown as it relies on a sight picture, and the rate of climb and rearwards speed need judgement rather than fixed parameters. It also introduces the risk of backing into an obstacle if not properly assessed.
I've flown and trained both, and variations on them, including a hideous home-concocted company version for the B212 which was easily mishandled and was not a bunch of fun having to sit along during base checks/OPCs (actually caused more spread skids during training than actual engine failure events!)
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JimL
Now double the exposure time to the tail rotor in a reverse climb and what does that do to the orders of magnitude...?
The failure rates for engines and tail-rotors (should) differ by four orders of magnitude.
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Like ShyT I do at least one Class 1 back up each working day. It is the safest way to operate. There is always power in hand, the profile is written that way, the reject in the event of a power failure simple and easily controlled. You're putting the whole back up out of proportion. And as FNW says "it keeps you out of the avoid curve." and he should know, he's been teaching this stuff for long enough, and in his current job deals with these profiles several times a day.
Don't try to re-write the laws of physics, they were written long before you and I came along, and they work just fine. I'd always prefer a class 1 back up from most sites to batting along with the collective under my armpit. The only one I had any real doubts about was the S76 vertical, which is quite an aggressive, full power manouvre.
SND
There is no Exposure Time in Category A operations.
'The reliability programme of aircraft in operation and maintenance is a combination of statistic monitoring and recording of the events associated with the airworthiness of an aircraft. The results obtained by monitoring reliability in operation may serve as a basis for supplementing or modifying the aircraft maintenance programme; such changes would indicate the malfunction of components or systems manifesting lacks and the need for early control, or replacement during utilization.'
https://www.maintworld.com/R-D/Aircr...lity-Programme
Any failure of a tail-rotor in a larger aircraft results in a challenge to the pilot - as you have seen from experiences shared on other threads.
Helicopters are certificated on an understanding that they will meet the projected reliability rates. If they do not, it is for the Airworthiness Authority to establish a route to rectification. This can result in amendment to maintenance procedures but cannot mitigate the event that causes the review.
JimL
'The reliability programme of aircraft in operation and maintenance is a combination of statistic monitoring and recording of the events associated with the airworthiness of an aircraft. The results obtained by monitoring reliability in operation may serve as a basis for supplementing or modifying the aircraft maintenance programme; such changes would indicate the malfunction of components or systems manifesting lacks and the need for early control, or replacement during utilization.'
https://www.maintworld.com/R-D/Aircr...lity-Programme
Any failure of a tail-rotor in a larger aircraft results in a challenge to the pilot - as you have seen from experiences shared on other threads.
Helicopters are certificated on an understanding that they will meet the projected reliability rates. If they do not, it is for the Airworthiness Authority to establish a route to rectification. This can result in amendment to maintenance procedures but cannot mitigate the event that causes the review.
JimL
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SND
My point exactly, catering for event of power failure on very reliable engines (and you have two of them) and not catering for event of tail rotor failure and in so doing increasing exposure time too.
Except not in this case...
the profile is written that way, the reject in the event of a power failure
they were written long before you and I came along, and they work just fine.
Now double the exposure time to the tail rotor in a reverse climb and what does that do to the orders of magnitude
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212man;
Please feel free to borrow my wall to bang your head against! You're arguing with the man who believed that taking off overweight was fine so long as you didn't overtorque or over temp. That took nearly 6 pages sto get some common sense going.
Chop; pay heed to JimL, he was my Senior Pilot once, knows his way round an aircraft and was the policy man at CAA and JAR where all this stuff was decided.
SND
Please feel free to borrow my wall to bang your head against! You're arguing with the man who believed that taking off overweight was fine so long as you didn't overtorque or over temp. That took nearly 6 pages sto get some common sense going.
Chop; pay heed to JimL, he was my Senior Pilot once, knows his way round an aircraft and was the policy man at CAA and JAR where all this stuff was decided.
SND
My feeling is that a rapid throttle chop and attempted AUTO from 120-200 feet and zero IAS may not be the obvious answer.
No, I've taken to sticking needles in my eyes - it's much more enjoyable!
My only comment and observation with respect to tail rotor drive failures and reaction time is; they don't happen without an associated thud, clunk, clatter, grinding noise or preceding high frequency vibration. As handling pilot, you should be in no doubt when the excessive yaw rate that you're experiencing, with the power pedal fully forward, is a tail rotor drive failure.
Several hundred horse power going through the tail rotor drive system doesn't fail 'quietly'. In many of the simulator sessions that I've experienced, these essential clues were often missing.
JJ
Several hundred horse power going through the tail rotor drive system doesn't fail 'quietly'. In many of the simulator sessions that I've experienced, these essential clues were often missing.
JJ
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A back up procedure to a TDP of 200 ft isn't going to take double the time to reach 200 ft in a vertical climb - why would it?
Now using same criteria going backwards, having less (if no) head wind, using more pedal (and therefore more power) and having a longer distance to go (The hypotenuse) with same power available will obviously reduce ROC, then you have to rotate even more at the top (from nose up attitude to nose down).Then allow time to accelerate forwards to zero GS. So taking twice as long is a guess on my part, but every one I have seen appears to take twice as long as a simple up, rotate and away.
Psychophysiological entity
My only comment and observation with respect to tail rotor drive failures and reaction time is; they don't happen without an associated thud, clunk, clatter, grinding noise or preceding high frequency vibration.
Chopjock,
Not all aircraft prescribe climbing at MTOP during a VTOL procedure so your rate of climb calculation is flawed. Most outline a rate of climb to maintain so 200ft vertically or 200ft backwards will be reached at the same time.
FNW
Not all aircraft prescribe climbing at MTOP during a VTOL procedure so your rate of climb calculation is flawed. Most outline a rate of climb to maintain so 200ft vertically or 200ft backwards will be reached at the same time.
FNW
Choppy - you are a cad arent you.
You're stubborn, I'll give you that.
we've established you have learning difficulties over the years so lets make it simple......again:
When a component is found to fail less often than another, checks and measures are reduced appropriately.
in the case of engines Vs tail rotors, its in the region of 4:1.
Our "authorities" bless them all, have experience and access to experts and stats.
With these tools, they risk manage the issue and produce best practice. If it doesn't work, they review.
No-one has come up with a better solution yet but i am sure they would love to hear from you.
Commercial ops departures have been revised and reviewed several times over the years as the odd engine failure pops up.
But sorry to burst your bubble choppie but tail rotor failures during departure (even when they are under extra strain) don't feature much in the stats.
Now i know we are a nanny state in the UK but we haven't quite reached the stage where every problem requires evasive manouevres - yet. If we did we'd either engineer tail rotors out of existence or stop flying altogether.......there....is that easier to understand?
Remember choppie....we're not talking about those radio controlled helos you fly.........
SEE POST NUMBER 79
You're stubborn, I'll give you that.
we've established you have learning difficulties over the years so lets make it simple......again:
When a component is found to fail less often than another, checks and measures are reduced appropriately.
in the case of engines Vs tail rotors, its in the region of 4:1.
Our "authorities" bless them all, have experience and access to experts and stats.
With these tools, they risk manage the issue and produce best practice. If it doesn't work, they review.
No-one has come up with a better solution yet but i am sure they would love to hear from you.
Commercial ops departures have been revised and reviewed several times over the years as the odd engine failure pops up.
But sorry to burst your bubble choppie but tail rotor failures during departure (even when they are under extra strain) don't feature much in the stats.
Now i know we are a nanny state in the UK but we haven't quite reached the stage where every problem requires evasive manouevres - yet. If we did we'd either engineer tail rotors out of existence or stop flying altogether.......there....is that easier to understand?
Remember choppie....we're not talking about those radio controlled helos you fly.........
SEE POST NUMBER 79
Last edited by Thomas coupling; 4th Nov 2018 at 14:24.
I've flown and trained both, and variations on them, including a hideous home-concocted company version for the B212
I always felt like a proper dolt performing that take off as I looked down a nice long runway in front of me with thousands of feet of concrete well in excess of anything I would need to use during a rejected takeoff.....but what ho Skippy....it is the way we do things here.
At another Operator in the USA that is very well known for using EMS Airbus Singles for spontaneous bonfires....It was their policy during OEI landings in the 412 to make a shallow approach at 60 knots until 50-75 feet from the surface and then "dive" to get within a few feet of the surface so as to "be in ground effect" while making the run on landing well above translational airspeed.
When asked what would happen if the remaining engine failed while the "diving" to the surface (think nose down, descending, and very close to the ground while you consider that statement.....they opined no problem....just do as we say.
Had I not feared dying in the crash.....I thought about rolling off the throttle during one of those approaches on a Check Ride but always chickened out before doing so.
What I did do.....is follow the policy while doing the check ride then do what every operator of Twins advocated in doing OEI Landings.....omitting the diving part.
Somehow I always reach a conclusion that these kinds of things get over thought by the authorities because of factors not related to the actual safe operation of the aircraft.
Engines should meet a reliability figure of 1 x 10**-5; in ICAO parlance, this qualifies them as very reliable (the reason for the low standard is that a failure, at worst, should only result in an outcome of 'Major' - i.e. 'physical distress including injuries).
Tail-rotors should meet a reliability figure of 1 x 10**-9 because a failure could result in an outcome of 'Hazardous' or 'Catastrophic' - i.e. a fatality or multiple fatalities.
Reliability targets for tail-rotors are therefore 4 orders of magnitude better than engines - i.e. 10,000.
(A probability does not mean that a failure will occur after the reliability number has been reached, it can occur at any time but it should only occur once in the period.)
A helicopter certificated in Category A can depart or arrive utilising Category A procedures where failure of an engine should not result in damage.
A single-engine helicopter can depart or arrive using a Category B procedure where failure of the engine should not result in damage. It does this by accelerating below the HV avoid curve until it achieves a climb speed clear of the 'knee' of the HV curve.
Any departure other than that published in the Flight Manual - for either a Category A or Category B helicopter - could, following an engine-failure, result in a 'Hazardous' or 'Catastrophic' outcome (with a probability for a single of 1 x 10**-5, or for a twin or 2 x 10**-5).
An engine-failure in the cruise for a twin will be a non-event. An engine-failure in the cruise for a single might result in an outcome of 'Major' (as above) unless it is being flown over a hostile environment in which case the outcome might be 'Hazardous' or 'Catastrophic'.
In the recent accident, the profile flown was the AW169 Category A procedure. Whatever caused the accident was not the result of having flown this procedure. It was within the defined and certified operational envelope.
JimL
Tail-rotors should meet a reliability figure of 1 x 10**-9 because a failure could result in an outcome of 'Hazardous' or 'Catastrophic' - i.e. a fatality or multiple fatalities.
Reliability targets for tail-rotors are therefore 4 orders of magnitude better than engines - i.e. 10,000.
(A probability does not mean that a failure will occur after the reliability number has been reached, it can occur at any time but it should only occur once in the period.)
A helicopter certificated in Category A can depart or arrive utilising Category A procedures where failure of an engine should not result in damage.
A single-engine helicopter can depart or arrive using a Category B procedure where failure of the engine should not result in damage. It does this by accelerating below the HV avoid curve until it achieves a climb speed clear of the 'knee' of the HV curve.
Any departure other than that published in the Flight Manual - for either a Category A or Category B helicopter - could, following an engine-failure, result in a 'Hazardous' or 'Catastrophic' outcome (with a probability for a single of 1 x 10**-5, or for a twin or 2 x 10**-5).
An engine-failure in the cruise for a twin will be a non-event. An engine-failure in the cruise for a single might result in an outcome of 'Major' (as above) unless it is being flown over a hostile environment in which case the outcome might be 'Hazardous' or 'Catastrophic'.
In the recent accident, the profile flown was the AW169 Category A procedure. Whatever caused the accident was not the result of having flown this procedure. It was within the defined and certified operational envelope.
JimL
Last edited by JimL; 4th Nov 2018 at 13:22.
make a shallow approach at 60 knots until 50-75 feet from the surface and then "dive" to get within a few feet of the surface so as to "be in ground effect"