Shetland Chinook legacy remembered
Never having flown the Chinook. nor having been employed by that company except for a 3 month interlude, I feel eminently qualified to comment on its suitability as an offshore public transport machine.
I have been employed as a North Sea pilot for 3 decades and it takes no great intelligence to appreciate that the inherent weakness of the Chinook design is the importance of keeping the rotors synchronised.
Hence THREE of the five gearboxes ARE SUPERCRITICAL as a failure in any one of them will cause the rotor blades to clash. This is not true of other conventional helicopter designs, where a failure in either gearbox isn't necessarily going to have immediate fatal consequences.
From vague memory, the Chinook ditching certification trials were performed in a wave tank, probably using a model airframe in a relatively gentle sea state. But on an average North Sea day with wave heights of around 3 metres, the low-mounted Chinook front rotor would inevitably hit a wave before the rotors could be stopped and the ensuing breakage of a synchronising driveshaft or gearbox would allow front and rear rotors to clash.
Fatalities from flailing blades chopping into the cabin are almost guaranteed. Now who's going to try and convince me that I shouldn't give opinions on something I know nothing about? Don't waste the effort. Non-BAH/BIH pilots were discussing this aspect long before the disaster; I remember it all too well.
I have been employed as a North Sea pilot for 3 decades and it takes no great intelligence to appreciate that the inherent weakness of the Chinook design is the importance of keeping the rotors synchronised.
Hence THREE of the five gearboxes ARE SUPERCRITICAL as a failure in any one of them will cause the rotor blades to clash. This is not true of other conventional helicopter designs, where a failure in either gearbox isn't necessarily going to have immediate fatal consequences.
From vague memory, the Chinook ditching certification trials were performed in a wave tank, probably using a model airframe in a relatively gentle sea state. But on an average North Sea day with wave heights of around 3 metres, the low-mounted Chinook front rotor would inevitably hit a wave before the rotors could be stopped and the ensuing breakage of a synchronising driveshaft or gearbox would allow front and rear rotors to clash.
Fatalities from flailing blades chopping into the cabin are almost guaranteed. Now who's going to try and convince me that I shouldn't give opinions on something I know nothing about? Don't waste the effort. Non-BAH/BIH pilots were discussing this aspect long before the disaster; I remember it all too well.
Oh, the folly of...
"3 of the five" may be 'supercritical' but no less and no more critical than "1 out of one" - It's not as though you disconnect everything after every landing - or fold blades every night? - A bit of a non-argument really.
Having been onboard during Chinook water landings I can say that they can cope well with some spashy scenes - probably just as much as others can. I cant say about Fwd blade clearances, but I'm sure there are less worried about tail blades.
Having worked on the end results of three CH47 incidents - no-one was chopped up by blades coming through the sides, although at least two people I know were pushed off their seats.
When walking towards one incident I asked a senior pilot if the lack of a cockpit roof, rotor and gearbox would shake him? - to which he said that many other helis would have shaken themselves apart in the air, well before this particular event - in which all aboard survived without any significant injuries.
Your statements seem to be myth-guided?
"3 of the five" may be 'supercritical' but no less and no more critical than "1 out of one" - It's not as though you disconnect everything after every landing - or fold blades every night? - A bit of a non-argument really.
Having been onboard during Chinook water landings I can say that they can cope well with some spashy scenes - probably just as much as others can. I cant say about Fwd blade clearances, but I'm sure there are less worried about tail blades.
Having worked on the end results of three CH47 incidents - no-one was chopped up by blades coming through the sides, although at least two people I know were pushed off their seats.
When walking towards one incident I asked a senior pilot if the lack of a cockpit roof, rotor and gearbox would shake him? - to which he said that many other helis would have shaken themselves apart in the air, well before this particular event - in which all aboard survived without any significant injuries.
Your statements seem to be myth-guided?
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When walking towards one incident I asked a senior pilot if the lack of a cockpit roof, rotor and gearbox would shake him? - to which he said that many other helis would have shaken themselves apart in the air, well before this particular event - in which all aboard survived without any significant injuries.
The entire top deck was empty, rotor system, gearboxes, pylons, the lot, all gone.
Hence THREE of the five gearboxes ARE SUPERCRITICAL as a failure in any one of them will cause the rotor blades to clash. This is not true of other conventional helicopter designs, where a failure in either gearbox isn't necessarily going to have immediate fatal consequences.
Yes the Chinook has three very important gear boxes...FWD, AFT, and Combining....and yes...if one of them fails you have had the schnitzel...but in how many other helicopters does one not become sausage following a MGB failure?
One can argue there is three times the chance..but that is a fallacy. One must compare the actual rate of MGB failures by aircraft type per flying hour and then make an argument based upon that data.
I feared something getting under the Synch Shaft far more than I ever worried about a Gear Box failure....as they were pretty much unheard of whereas the loss of Synch shafts had occurred. Just as riveted ends of control tubes happened for a while. We even had blades rotatiing in the cuff due to Incidence Bolt failures....but yet the Chinook matured and those problems were cured/solved and became things of the past.
Bad maintenance seems to be the major culprit in any aircraft loss these days....except when Pilots forget how to move the sticks after letting the Auto Pilot do the driviing too much.
Much was made about Quill Shaft failures....but not once did I ever hear of that particular shaft failing as it was so over engineered and built way beyond the strenght it needed to be...that it was more an Old Wive's Tale than a genuine risk.
Anyone that diss's the Chinook is just suffering from Penis Envy in my book.
ShyTorque,
That is BBs soft-top incident indeed. And I was asking a 7 Sqn S/L at the time. my job was to remove the Aft Xmsn - which I did...horizontally.
"...where a MRB gearbox seized in the hover?"
No, it didn't. The Xmsn input shaft thrust bearing had been installed the wrong way round. It moved and allowed the drive gear to dissengage.
SaSless...
Impedence Bolts. I was lucky enough to have a fascinating conversation with an AAIB investigator regarding Impedence Bolts while investigating another accident.
...No. I wasnt working on any Sqn at the time.
That is BBs soft-top incident indeed. And I was asking a 7 Sqn S/L at the time. my job was to remove the Aft Xmsn - which I did...horizontally.
"...where a MRB gearbox seized in the hover?"
No, it didn't. The Xmsn input shaft thrust bearing had been installed the wrong way round. It moved and allowed the drive gear to dissengage.
SaSless...
Impedence Bolts. I was lucky enough to have a fascinating conversation with an AAIB investigator regarding Impedence Bolts while investigating another accident.
...No. I wasnt working on any Sqn at the time.
I think it is obvious to everybody that that is not a water landing... Big rotorwash, coning angles etc. That is just washing the dust off the bottom of the aircraft. There is a SK76, without flotation gear inflated, that has inadvertently gone into the water deeper than that and has flown away.
I'd like to see that "water-skimming" exercise done with 3 metre waves, or alternatively with the collective fully down in 1.5 metre waves. Either way the outcome wouldn't be pretty.
How does the 225/Super Puma do in the same conditions of three meter waves and no floatation? Any reason there is a move to add "Righting" floats to keep the aircraft right side up or at least on one side rather than wrong side up?
Compare apples to apples!
Compare apples to apples!
They (225/Super Puma) don't have inter-meshing rotors. That's been my central point since I made my first unwelcome comment. I'm by no means the first to comment on this and I can't understand why others turn a blind eye to the consequences of rotor synchronisation being lost after one rotor hits a wave before the other.
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I'll join in on colibri's side.
I worked with 2 of the people who died in that crash and flew as self loading freight 4 or 5 times on Chinooks - so I do not have a high opinion of them.
From the freight's viewpoint they were noisy, cramped and difficult to get into and out of - and that was without there being a problem and having to use the limited escape routes.
Helicopters tend to be very intolerant of transmission failures generally - introducing a variety of new and interesting failure modes in addition to those of a single rotor helicopter, means that either the design, engineering and maintenance has to be considerably better to maintain the SAME level of safety.
That situation may now have been achieved with the military variants - but somehow I doubt it. Certainly it has its uses in terms of heavy lift but not for people. Or at least not people who can choose.
I worked with 2 of the people who died in that crash and flew as self loading freight 4 or 5 times on Chinooks - so I do not have a high opinion of them.
From the freight's viewpoint they were noisy, cramped and difficult to get into and out of - and that was without there being a problem and having to use the limited escape routes.
Helicopters tend to be very intolerant of transmission failures generally - introducing a variety of new and interesting failure modes in addition to those of a single rotor helicopter, means that either the design, engineering and maintenance has to be considerably better to maintain the SAME level of safety.
That situation may now have been achieved with the military variants - but somehow I doubt it. Certainly it has its uses in terms of heavy lift but not for people. Or at least not people who can choose.
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It is telling how virtually all pilots who have flown the Chinook love and trust it while its pax who have flown in it 3 or 4 times seem happy to join in a safety-centred debate slagging it of and implying it unsafe on the basis of it being "noisy and uncomfortable" or leaking oil on their bags...
I think this amply illustrates the difference between decisions/judgements made from a position of knowledge and kneejerk prejuduices made with no knowledge or factual basis whatsoever. The tragedy is that in this crazy world of ours the latter is sometimes allowed to overrule the former when in reality it isn't even worth acknowleging. I think all is's pilots would agree that the 234 was lacking in comfort - it was cramped, 40 seats - one less row would have been better, the windows were small, but what's that got to do with anything? Vibrate? Nonsense. Not in the cruise it didn't. The dynamic vib control (the saddle-tanks were mounted on nodal beams) worked well but could and did cause larger than normal vibration at certain phases of flight, usually t/o and landing. But so what? That's a transient comfort matter, nothing related to safety. Emergency exits I agree were insufficient and I think all the pilots acknowledged that too. That was an unforseen error made at the time of ordering them.
I am not convinced by the argument that blades would strike the water in a ditching either, while turning the front blades were well out of harm's way and only drooped at very low speed when a strike would not be dangerous. Not many waves are steep enough to reach a point perhaps 3-4 metres high before they've lifted the hull just beyond. Sounds rather far-fetched (no pun intended) to me, and I'm sure must have been examined in the certification process. A ditching in such severe conditions would overturn a conventioonal helo almost instantly and almost certainly be unsurvivable even if egress was made. I know for sure which one I'd prefer to be in.
And to the poster who triumphantly pointed out the capsizing of the ditched BV234 (I didn't think it would take long for that pavlovian response to appear) for your information this had nothing whatsoever to do with the aircraf's stability as you yourself inadvertently pointed out. It floated as stably as a barge but eventually overturned due to water entering the cabin over a period of time past the aft bulkhead dam, a rubber seal like a car door seal had been torn by passing personnel and baggage over the preceeding months and did not seal properly. The hull loss was directly attributable to a ten dollar piece of rubber seal. That was an expensive lesson on the back of a safe and successful ditching that proved the types ability to cope easily with the event.
I think this amply illustrates the difference between decisions/judgements made from a position of knowledge and kneejerk prejuduices made with no knowledge or factual basis whatsoever. The tragedy is that in this crazy world of ours the latter is sometimes allowed to overrule the former when in reality it isn't even worth acknowleging. I think all is's pilots would agree that the 234 was lacking in comfort - it was cramped, 40 seats - one less row would have been better, the windows were small, but what's that got to do with anything? Vibrate? Nonsense. Not in the cruise it didn't. The dynamic vib control (the saddle-tanks were mounted on nodal beams) worked well but could and did cause larger than normal vibration at certain phases of flight, usually t/o and landing. But so what? That's a transient comfort matter, nothing related to safety. Emergency exits I agree were insufficient and I think all the pilots acknowledged that too. That was an unforseen error made at the time of ordering them.
I am not convinced by the argument that blades would strike the water in a ditching either, while turning the front blades were well out of harm's way and only drooped at very low speed when a strike would not be dangerous. Not many waves are steep enough to reach a point perhaps 3-4 metres high before they've lifted the hull just beyond. Sounds rather far-fetched (no pun intended) to me, and I'm sure must have been examined in the certification process. A ditching in such severe conditions would overturn a conventioonal helo almost instantly and almost certainly be unsurvivable even if egress was made. I know for sure which one I'd prefer to be in.
And to the poster who triumphantly pointed out the capsizing of the ditched BV234 (I didn't think it would take long for that pavlovian response to appear) for your information this had nothing whatsoever to do with the aircraf's stability as you yourself inadvertently pointed out. It floated as stably as a barge but eventually overturned due to water entering the cabin over a period of time past the aft bulkhead dam, a rubber seal like a car door seal had been torn by passing personnel and baggage over the preceeding months and did not seal properly. The hull loss was directly attributable to a ten dollar piece of rubber seal. That was an expensive lesson on the back of a safe and successful ditching that proved the types ability to cope easily with the event.
CH-47 Water Ops
The following pics from a February 1965 test at Ft Rucker on a new A model with a rear dam kit:
( Probably should add, relative to the discussion at hand, that this machine did not have a rotor brake. Surely the 234 would have had one, and most likely the emergency procedures would have cited an immediate, full on application after a water landing in high sea state. I don't know the 234, but one would assume the rotor brake disc would be located between the combining box and the aft transmission. 234 pilots can correct this info.
( Probably should add, relative to the discussion at hand, that this machine did not have a rotor brake. Surely the 234 would have had one, and most likely the emergency procedures would have cited an immediate, full on application after a water landing in high sea state. I don't know the 234, but one would assume the rotor brake disc would be located between the combining box and the aft transmission. 234 pilots can correct this info.
Last edited by JohnDixson; 10th Nov 2011 at 13:50. Reason: Additional Comment
"Vibrate? Nonsense. Not in the cruise it didn't."
One of my colleagues used to fly it regularly as a co-pilot on flights between Aberdeen and the East Shetland Basin. He told me that it was not uncommon for him and others to get off the co-pilot's seat during the cruise to get some relief from the vibration.
Exactly how he did that I don't know. Whether he just lifted himself partially from the seat for a short while, or whether he vacated the flight deck is irrelevant. What is certain is that he found the vibration sufficient to give him headaches and backaches.
I can empathise with your sentimental attachment to the Chinook. I'm sentimentally attached to the S61N, but that doesn't make me blind to its weak points such as being seriously underpowered on one engine.
Have you actually seen the steepness and short intervals of waves on the North Sea on a rough day? If you think that one of the rotors (particularly the front) wouldn't contact the water until the blades were drooping to a standstill, then you need a reality check.
Yes, I'm envious of those who've flown it, but not to the extent that I'd have wanted to spend much time in the Chinook over rough water. This line of argument is already pointless, so I'd better just leave you and all with real experience on the type to selective reminiscences.
One of my colleagues used to fly it regularly as a co-pilot on flights between Aberdeen and the East Shetland Basin. He told me that it was not uncommon for him and others to get off the co-pilot's seat during the cruise to get some relief from the vibration.
Exactly how he did that I don't know. Whether he just lifted himself partially from the seat for a short while, or whether he vacated the flight deck is irrelevant. What is certain is that he found the vibration sufficient to give him headaches and backaches.
I can empathise with your sentimental attachment to the Chinook. I'm sentimentally attached to the S61N, but that doesn't make me blind to its weak points such as being seriously underpowered on one engine.
Have you actually seen the steepness and short intervals of waves on the North Sea on a rough day? If you think that one of the rotors (particularly the front) wouldn't contact the water until the blades were drooping to a standstill, then you need a reality check.
Yes, I'm envious of those who've flown it, but not to the extent that I'd have wanted to spend much time in the Chinook over rough water. This line of argument is already pointless, so I'd better just leave you and all with real experience on the type to selective reminiscences.
Last edited by Colibri49; 10th Nov 2011 at 12:45.
Do I know what the North Sea looks like....Yes.
Given a choice of the Chinook or any other type that is or has ever worked the North Sea Oil Support industry.....without a single second's hesitation it would be the Chinook (234) as first choice!
As to my choice of aircraft to ditch in the North Sea...again without a second's hesitation it would have been the 234 as it is one very large boat with a lot of inherent stabilty due to its length and width.
Likewise as a Pilot...the spring assisted jettisonable crew doors is a big plus. No hunting for a way out in the Chinook.
As a passenger...that might be a much different kettle of fish. The seating decision was made by the customer, the exits were dictated by the customer, thus I cannot fault the aircraft for that situation...but do fault those making the decisions.
I have played boat captain in the Wokka.....and she makes a very fine boat she does. She was designed to be landed in the water as a part of normal operations. That is a good start if one has to "ditch".
Is not one of the questions the Industry struggles with is when to limit aerial operations due to Sea State conditions?
And...it is the one that generally has been ignored the most all these years and still does not have a effective answer in place!
Given a choice of the Chinook or any other type that is or has ever worked the North Sea Oil Support industry.....without a single second's hesitation it would be the Chinook (234) as first choice!
As to my choice of aircraft to ditch in the North Sea...again without a second's hesitation it would have been the 234 as it is one very large boat with a lot of inherent stabilty due to its length and width.
Likewise as a Pilot...the spring assisted jettisonable crew doors is a big plus. No hunting for a way out in the Chinook.
As a passenger...that might be a much different kettle of fish. The seating decision was made by the customer, the exits were dictated by the customer, thus I cannot fault the aircraft for that situation...but do fault those making the decisions.
I have played boat captain in the Wokka.....and she makes a very fine boat she does. She was designed to be landed in the water as a part of normal operations. That is a good start if one has to "ditch".
Is not one of the questions the Industry struggles with is when to limit aerial operations due to Sea State conditions?
And...it is the one that generally has been ignored the most all these years and still does not have a effective answer in place!
Not knocking the aircraft, but;
I would have thought that the holes in the side were put in by the manufacturer. He would have modified those holes according to the regulations of the country that the aircraft was to be registered in. There was no further requirement in this particular case so the customer had no decision to make.
I was among the first to volunteer to fly the Chinook when it was mooted that Bristow may buy them. I missed out on that for obvious reasons. I regret not being able to fly it as I would have done if I had remained in the Royal Air force. However, at the end of the day, the 332L was the better helicopter for the North Sea; and this has been proven by the almost universal application of it worldwide on long range offshore applications.
This thread is getting like the Harrier thread on the military forum. It's gone, sorry, there's nothing you can do can bring it back. Let the subject rest.
the exits were dictated by the customer,
I was among the first to volunteer to fly the Chinook when it was mooted that Bristow may buy them. I missed out on that for obvious reasons. I regret not being able to fly it as I would have done if I had remained in the Royal Air force. However, at the end of the day, the 332L was the better helicopter for the North Sea; and this has been proven by the almost universal application of it worldwide on long range offshore applications.
This thread is getting like the Harrier thread on the military forum. It's gone, sorry, there's nothing you can do can bring it back. Let the subject rest.
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I think that some here are forgetting one very important thing.
The pilots only fly the aircraft. Like it or not, the passengers of a civilian aircraft are the customers. Nothing much else counts.
The pilots only fly the aircraft. Like it or not, the passengers of a civilian aircraft are the customers. Nothing much else counts.
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Colibri, it can be utterly maddening how some people argue from the specific to the general on this forum, and how it seems to be necessary to write caveats to every contrary eventuality when making a simple point.
I said it did not vibrate in the cruise and thought I'd qualified enough with my extensive explanation. Evidently not enough though... as I was discussing the pax it didn't occur to me that someone might want to bring the flighdeck into it. My mistake! The LH seat in the 234 was sited at probably the strongest vibration node in the aircraft and could be uncomfortable at tines. One of those frequencies was resonant freq of the end of the human nose which made it tickle and bring on a long-tern desire to sneeze. I certainly never felt the need to get out of my seat or suffered any physical effects and am a bit surprised anyone else did, I don't recall the vibes being that bad.
I haven't seen anything sentimantal here ignoring obvious faults - indeed the (relatively few) faults are being discussed in detail. Pilots tend to be more practical than sentimental which is why those who have the knowledge of this machine tend to prefer it over other more conventional craft, especially those that were unergonomic, labour intensive and grossly underpowered & short on range, frequently developed red-hot gearboxes or depended on the 100% success rate of several tetchy and delicate gasbags or they were guaraneed to fall over when ditched. I'd respectfully suggest that preference is founded on a sound Professional judgement of the respective merits of the various types rather than on sentimentality, and the result is petty conclusive.
And finally, no, as a Chinook, Seaking, S61 pilot, Naval person, Yachtsman and sand-castle builder I've clearly never seen waves on the N Sea. (sigh) Next question?
I wouldn't propose the 234 for anything but short public trips, but the N Sea was and is not a "public" environment. The pax are travelling to work on company provided transport so can't expect the levels of comfort that apply to bucket and spade trips. It is no different to miners going to work standing in a dark metal cage or fishermen/offshore windmill workers hanging on to a railing for grim death. I'd say they have it pretty good compared to many.
I said it did not vibrate in the cruise and thought I'd qualified enough with my extensive explanation. Evidently not enough though... as I was discussing the pax it didn't occur to me that someone might want to bring the flighdeck into it. My mistake! The LH seat in the 234 was sited at probably the strongest vibration node in the aircraft and could be uncomfortable at tines. One of those frequencies was resonant freq of the end of the human nose which made it tickle and bring on a long-tern desire to sneeze. I certainly never felt the need to get out of my seat or suffered any physical effects and am a bit surprised anyone else did, I don't recall the vibes being that bad.
I haven't seen anything sentimantal here ignoring obvious faults - indeed the (relatively few) faults are being discussed in detail. Pilots tend to be more practical than sentimental which is why those who have the knowledge of this machine tend to prefer it over other more conventional craft, especially those that were unergonomic, labour intensive and grossly underpowered & short on range, frequently developed red-hot gearboxes or depended on the 100% success rate of several tetchy and delicate gasbags or they were guaraneed to fall over when ditched. I'd respectfully suggest that preference is founded on a sound Professional judgement of the respective merits of the various types rather than on sentimentality, and the result is petty conclusive.
And finally, no, as a Chinook, Seaking, S61 pilot, Naval person, Yachtsman and sand-castle builder I've clearly never seen waves on the N Sea. (sigh) Next question?
I wouldn't propose the 234 for anything but short public trips, but the N Sea was and is not a "public" environment. The pax are travelling to work on company provided transport so can't expect the levels of comfort that apply to bucket and spade trips. It is no different to miners going to work standing in a dark metal cage or fishermen/offshore windmill workers hanging on to a railing for grim death. I'd say they have it pretty good compared to many.
Last edited by Agaricus bisporus; 10th Nov 2011 at 16:28.