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Robinson Safety Courses

Old 29th Oct 2001, 18:58
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For many years I (and many others) have avoided the Robbo. Against one's better judgement, I hear you say, I recently got checked out on the R22.
Every pilot who flies a Robbo will benefit from the safety course of that I am sure. It is a VERY light helicopter and has its own agenda.

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Old 30th Oct 2001, 13:51
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Lu,

Thanks for posting the POH. Nothing I have said seems to disagree with it other than the application of aft cyclic. It has shown me where you get the idea that flapping is so dangerous. As it says Lu, excessive flapping occurs during the sideslip of the aircraft. Same as I stated above: flapping is due to the acceleration/deceleration of the disc NOT due to cyclic application as you continue to assert. Sideslip is accelerating the disc in the direction of the sideslip causing a new flapping to equality to occur (which will be barely noticeable to the pilot), and flapback in that direction which will be noticeable, coupled with the attendant fuselage roll, and pitch up or down dependant upon rotor direction. The pitch can actually be quite severe, but is often not considered. It is these forces that add to the danger of mast bump. Cyclic application is not the same thing as side slip.

Summary: Cyclic input does not cause excessive flapping, sideslip can. Again – I think you have some fundamental misunderstandings about flapping. I will put my two cents worth in the other thread from DJ as well.
Lu, you say: >>Many of your objections to my comments are based on your knowledge of Bell flight theory and using that logic; you question or object to my postings about the Robinson.<< I agree to a point, but my objections are based on rotor theory, not just on Bell systems. I fundamentally reject some of your basic propositions – such as that the disc goes “wild” during zero G. You base your theories on these fundamental flaws, hence I take issue with them. I would like you to go back to the point form above so we can continue to nut out these issues, rather than meander onto generalisations.

You said >> Tim Tucker who was a test pilot during development of the R22 also teaches many safety courses. He tells the students to add a tad left cyclic when pulling back on the cyclic to load the main rotor. No other instructor has his experience or technical background and in their ignorance or whatever they follow the instructions in the POH.<<
As I said previously in reference to Tim Tucker, He knows his stuff and I don’t. I can only teach what the manufacturer recommends and what I can justify. Just curious though…if he was the test pilot, why did he not ensure that the POH included the application of left cyclic so that everyone could benefit from his results? Would be great to get him on pprune to hear what someone of his experience has to say.

You then say >>The POH says to bring the cyclic back without adding any lateral cyclic. If it can be proven at some later date that the 18-degree offset of the control system is a factor it can be proven that Tim Tucker was right and if you did the control movement in accordance with the POH you could increase the right roll rate. A highly experienced pilot could possibly recover from this situation. However if a newbie enters this condition he will most likely instinctively push the cyclic left and chop off his rotor or the tail boom.<<

This confuses me Lu. You say that a highly experienced pilot could recover from an increased right roll rate due to using the POH technique, but then you say a newbie will roll left and chop the tail boom off. Firstly, how does the experienced pilot recover from the right roll without using any left cyclic? Secondly – isn’t the newbie using Tim’s technique? What did you mean here? Thirdly - I believe mast bump would be the result, not chopping off the tail boom (although that may indeed occur subsequently).

Lastly you ask: >>one question. How many Bell Helicopters have a restriction against sideslip and out of trim flight?<<
The UH-1H certainly does, and I believe the 212 as well. It is something like “application of full pedal above 80 KIAS is prohibited”

Also it has prohibitions against negative or zero G manuevers as well as something about the rapid lowering of the collective from 45 psi will cause a pitch down and roll right and possibly mast bump. Any Huey/Bell gurus, please correct me if I am wrong.

In other words, the Bell does have restrictions WITHOUT an 18 degree offset OR conning hinges. What do you know?


Edited for (some of the ) spelling.

[ 30 October 2001: Message edited by: helmet fire ]
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Old 30th Oct 2001, 14:17
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helmet :

( I love being able to call someone that and get away with it ! ).

I think I'm the guy who posted the thing, aeons ago, about "aft and a tad of left cyclic" - I heard Tim Tucker say that during a discussion on low G when I was on my safety course in Oz, about 2.5 years ago ( reminder to self - go on another one soon ).

If my memory serves right, he said the reason that the "tad of left" cyclic wasn't included in the manual was that, although it increased the effectiveness of the recovery, it wasn't crucial and therefore was left out - if misjudged you can dig yourself deeper in the hole rather than recovering.

At the time, he ( Tim ) had about 15000 or so helicopter hours, and people with that level of experience I would imagine can pole pretty accurately and judge "a tad". I can't imagine someone with my hours being able to do quite the same and live to tell the tale . . .

BTW, he found out all about the exact techniques while test flying to EXPLORE the low G regime, until he realised he'd probably gone far enough without mishap.
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Old 30th Oct 2001, 15:14
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Fairy,
(I am a "tad" uncomfortable about calling anyone a fairy,but... )

Thanks for that. Makes perfect sense. One of the reasons I go ppruning is to hear from the Tim Tuckers of this world. I would love to hear his stories on all this. A test pilot exploring zero G in a teetering head must really know his stuff.
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Old 31st Oct 2001, 07:43
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To: helmet fire

I’ll try to respond to each paragraph as applicable.

We are looking at two different things. Sideslip and cyclic input. Cyclic (left) during recovery from a zero G situation can result in severe flapping. Sideslip in the case of the Robinson can also cause severe flapping. These are not my words they are published in the Robinson POHs for the R22 and R44.

My statement about the disc going wild alluded to the severe flapping when improperly recovering from a zero g situation.

Regarding Tim Tucker, as the test pilot he was required to bring any problems relative to handling qualities to the attention of the engineering group and the certification authorities. This is a requirement of the certification document for normal category helicopters. My question is did he notify Robinson of the problems. I would think that he did not or if he did Robinson did not react to the input. After many mast separations and rotor incursions additional research was performed and it was decided that in order to minimize the possibility of mast bumping the helicopter should be restricted from sideslipping and flying out of trim as both maneuvers would result in severe flapping and cause mast bumping and or rotor incursion.

The certification requirements for normal category rotorcraft require that sideslipping and flying out of trim be demonstrated in order to gain certification. Both the Robinson and the Bell had to demonstrate these maneuvers. It seems that the restriction of the sideslipping of the 205 and 212 sets the maximum speed at which side slipping can be accomplished. This restriction may have come out of the certification trials or later on as a result of an in service problem. The Robinson on the other hand is restricted totally from performing sideslip or out of trim flight at any speed. This was done to minimize the possibility of mast bumping. If you had followed my posts of last year I addressed whether the Robinson design was certifiable. If Frank Robinson were to place the two designs up for certification at this time the FAA would reject the design because they could not meet the certification requirements that dictate the performance of sideslip at 90-degrees and out of trim flight at 10-degrees at a specified speed. My basic question still stands. If the Robinson is restricted from sideslip and out of trim flight now because of the catastrophic results stemming from these maneuvers then how did it get through the certification process without this being discovered?

In accordance with Safety Notice SN-11 when entering zero G the tail rotor thrust will cause the helicopter to rapidly roll to the right. It specifically states not to try to counter the roll with cyclic input until you have loaded the main rotor. This is accomplished by gently bringing the cyclic aft. When the rotor is loaded the pilot can then use cyclic to counter the roll. In the case of a low time pilot the survival instinct may be stronger than his knowledge base and he moves the stick to the left and causes flapping which results in mast bumping/rotor incursion. If my contention of the 18-degree offset were correct then this would further exacerbate the problem by increasing the roll rate with the same results with the low time pilot. An experienced pilot could go with the roll after regaining control of the rotor and maneuver out of the roll into stable forward flight.
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Old 31st Oct 2001, 11:16
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Lu, do you even read my posts before replying? Examples:

a. you said: >>We are looking at two different things. Sideslip and cyclic input.<< This is the point I made to you above!

b. you said: >>Cyclic (left) during recovery from a zero G situation can result in severe flapping.<< You keep repeating this line without responding to my continued assertion that CYCLIC APPLICATION DOES NOT RESULT IN SEVERE FLAPPING. No, not even during zero G. Sideslip does, cyclic doesn’t. That’s why I brought up the differences between them. I say again Lu, you need to grasp the fundamentals of flapping.

c. You said: >>My statement about the disc going wild alluded to the severe flapping when improperly recovering from a zero g situation.<< There was no such inference in the statement. You have stated this on so many threads, including retreating blade stall, gyroscopic precession, etc, and at none of those times did you infer it was during a “recovery” situation. I will respond yet again that the disc DOES NOT behave wildly when using cyclic – even under zero G. Even during a recovery. See my first post on this thread.

d. You have ignored my repeated question: If a Bell system is vulnerable to mast bump in exactly the same circumstances as a Robbie, and it does NOT have the 18 degree offset, nor the flapping hinges – how can the 18 degree offset or flapping hinges be the culprit??????

e. Why do the mast bumping incidents of Bell helicopters not get your attention? I bet there has been just as many, if not a lot more due to time in service?

f. You state that: >>the helicopter [was] restricted from sideslipping and flying out of trim as both maneuvers would result in severe flapping and cause mast bumping and or rotor incursion.<< Isn’t flying out of trim and sideslipping the same thing? It is when I am flying.

g. Again we hit that old chestnut of cyclic causing severe flapping: >>he moves the stick to the left and causes flapping which results in mast bumping/rotor incursion<< Not true methinks Lu, See above.

You then state that :>>If my contention of the 18-degree offset were correct then this would further exacerbate the problem by increasing the roll rate<< Interesting assertion Lu, how do you think the offset increases roll rate? Do you believe this always happens, or only with zero G? If only with zero G, how does the G affect the offset?

Thanks for the back and forward Lu, it certainly helps keep back the cobwebs from flight school!

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Old 31st Oct 2001, 13:06
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Re the situation with mast-bumping/chopping of your tail boom, I fly very carefully, having read and re-read all of the journals especially the comments on Pprune from you very experienced pilots regarding the problems with Neg G on teetering head heli's, however my question is:-
If Neg G is entered, whether purposefully or by accident of the operating pilot, does anyone know what the time scale of incident is likly to be between entering Neg G and mast or tail separation, and if one did unfortunatly enter into Neg G, is that it, all over in say one, two or three seconds, or would you be able to recover to land back at base, or would it be to land urgently, and if having landed back at base, would that Heli then need a severe strip down check or would it be safe for the next flight?
I realise these may be "Crystal Ball" questions, but what I am trying to see is where are the limits to mast bumping/neg G, and could it be another flight/pilot that gets the prize, that has been lined up by an earlier incident?
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Old 31st Oct 2001, 13:20
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VFR :

I'm not convinced there are limits for negative G. Personally, if I ever got there I think the most important factor in deciding whether to get down on the ground would be the strength of the resulting smell in the cockpit.

Seriously, my tactics are 1) avoidance, 2) aft cyclic to reload, 3) DEEP breath, and finally 4) probably put the thing down immediately under power to reduce exposure time if the mast has been bumped because if I get past (1) I'd be a test pilot without the CV to back it up.
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Old 31st Oct 2001, 16:21
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As I'm attending the Nov safety course, is there anything anybody would like me to ask Frank or Tim ?

Should I ask whether they think the heli would pass re-certification ?
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Old 31st Oct 2001, 17:23
  #30 (permalink)  
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RSH

Where are you doing the course in Nov? Who did you contact to book on it and do you know if there is any space left on it?

Thanks
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Old 31st Oct 2001, 18:26
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I'm doing it at the factory in Torrence and I booked it way back in June. From looking at their web site, the next free spaces are in Feb but you could give them a call and see if anybody backs out.
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Old 31st Oct 2001, 20:29
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To: helmet fire

Here are my responses to your points A through G:

A) Sideslip according to the Robinson POH is to be avoided as it and out of trim flight will result in high flapping loads and cause mast bumping. The application of left cyclic during recovery from a zero g condition is to be avoided because it can result in high flapping loads causing mast bumping. Application of left cyclic or any other direction when flying within the normal envelope will NOT cause high flapping loads. This is why I differentiated sideslip and left cyclic during zero G recovery from the use of cyclic under normal conditions.


B) Please read A) above. If you have an argument with this then I would suggest you contact Robinson or, get a copy of the POH looking under section 4 (last page-unnumbered) and Safety Notice SN-11 as those are the sources that I quote.

C) It is true that the disc does not behave wildly under a zero G condition it is only if you apply left cyclic during the recovery that the flapping loads and frequency increase to the point of mast bumping. Once again this is in the POH.

D) If you can accept the possibility of there being an 18-degree offset in the controls when flying forward to compensate and allow the helicopter to fly forward then, you must understand that the pilot has inputted right cyclic to accomplish this. If in the recovery from a zero G incident the pilot pulls the cyclic aft in accordance with the POH he will have a right bias in his control input. It is this right bias that will add to the already prominent right roll and cause the helicopter to violently roll to the right. It is at this point experience comes into play. The highly experienced pilot can load the rotor and keep rolling the helicopter and bringing it back into stable flight. The inexperienced pilot will try to correct the roll before fully loading the rotor and cause mast bumping. Any application of left cyclic during recovery from zero G will result in mast bumping and under normal recovery from zero g there is a right roll component. If the 18-degree offset comes into play the condition will be further exacerbated.

I believe that this is why Tim Tucker told his students to add a tad left cyclic during recovery from zero G. He ,if I am correct was telling his students to compensate for the offset.

E) I was manager of Technical Assistance for Bell Helicopter International for three years and I was very aware of rotor loss and mast bumping on Bell Helicopters. At my last count during my association with Bell there had been 63 mast separations on several different models. It was during that time that Bell put rubber bumpers on the heads and strengthened the masts on the 205s. The Robinson has experienced over 30 mast separations to my recollection.

F) The Robinson POHs address sideslip and out of trim flight as two different things both of which should be avoided. The Normal Rotorcraft certification document also addresses the demonstration of out of trim and sideslip as two different things both of which must be demonstrated for certification.

G) Once again your argument is with the Robinson POHs and not with me.

Your final paragraph is answered above.

[ 31 October 2001: Message edited by: Lu Zuckerman ]
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Old 31st Oct 2001, 20:47
  #33 (permalink)  

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To: Rock_Steady_Hover

“As I'm attending the Nov safety course, is there anything anybody would like me to ask Frank or Tim ?
Should I ask whether they think the heli would pass re-certification ? “

Ask the following: Since the Robinson helicopters are restricted from sideslip and out-of-trim flight can the R22 and R44 meet the requirements of the Certification Requirements for Normal Category Rotorcraft which require demonstration of both to include 90-degree sideslip and 10-degree out of trim.

Also ask them to explain how their rotor system that has an 18-degree offset behaves with a phase angle of 72-degrees as opposed to 90-degrees on other rotorheads. Ask them why on the various Robinson websites they address the Robinson rotorhead yet when they address gyroscopic precession they use a Bell related diagram.
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Old 31st Oct 2001, 21:14
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RSH,
Upon reading this thread again , I think it may be a good question to ask FR(thats if he'll answer it)regarding whether to recover to base or land PDQ after recovering from a Neg G situation.
TNF, on recollection I feel that I may have just escaped or possible just entered a Neg G situation on a flight in a R22 late spring 2001, I passed over a cliff face to find a humongous updraft trying to push the tail over the top of me, the A/c did roll slightly right, but besides that smell that you refer to, I dumped the power and eased straight back on the stick, within about 8 secs everything was back to normal and slowly increasing the power I resumed my journey, but the more I think about that particular piece of that flight I think possibly I was there,or at least knocking on the door, as I always do a post check after flight I found nothing wrong,that I could see, and after talking to the Cfi it was just put down to one of those things that you get in turbulance, but, I hasten to add, I have watched the Tec log of that crate, and no one so far has made any comments about it, so it would be nice to know, what FR thinks about the servicablity after a major Neg G incident!
From my little explanation above what do you chaps think?
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Old 31st Oct 2001, 21:47
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""D) If you can accept the possibility of there being an 18-degree offset in the controls when flying forward to compensate and allow the helicopter to fly forward then, you must understand that the pilot has inputted right cyclic to accomplish this. If in the recovery from a zero G incident the pilot pulls the cyclic aft in accordance with the POH he will have a right bias in his control input. It is this right bias that will add to the already prominent right roll and cause the helicopter to violently roll to the right. It is at this point experience comes into play. The highly experienced pilot can load the rotor and keep rolling the helicopter and bringing it back into stable flight. The inexperienced pilot will try to correct the roll before fully loading the rotor and cause mast bumping. Any application of left cyclic during recovery from zero G will result in mast bumping and under normal recovery from zero g there is a right roll component. If the 18-degree offset comes into play the condition will be further exacerbated.""


OK Lu, reread the above please, I quoted from your post. I'll clarify. The whole point of not adding lateral cyclic during negative G is that it will NOT, EVER, FOR ANY REASON, roll the aircraft, it moves the disc independantly of the fuselage and can, if severe enough, result in mast bumping.

Assuming you hold the stick perfectly still laterally, the disc will sense a right cyclic input as zero G is encountered, the fuselage rolls, and the positional relationship between disc and fuselage changes. This doesn't kill you. Keep in mind we are talking about a very quick sequence of events. See below:

OK, the disclaimer, DON'T TRY THIS AT HOME!

If the a/c is pushed over into zero G with cyclic and the pedal is pushed hard right what happens? No roll, just a really scary feeling. The disc doesn't commit a hairy fit. If the left pedal is not taken out the roll is extremely rapid and will scare you. Unless you are mentally prepared for it you will instinctively react with opposite cyclic and die. Any procedure written into a manual is written for "THE LOWEST COMMON DENOMINATOR". I've helped write some of these rules/procedures and that's how it works. If you write in the book to add left cyclic and the intent is for a 1/4 inch movement, good luck, it'll never happen.
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Old 31st Oct 2001, 21:51
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To: Vfr

I may be talking out of the back of my head and I don’t know if Frank Robinson or for that matter anyone else would agree. However it seems to me that as long as the pilot does not induce high flapping loads and the resultant mast bumping, the main rotor is operating at well below normal stress levels during the period of zero G and as such, there should be no mechanical problems resulting from the incident.

Anybody else got any other ideas?
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Old 1st Nov 2001, 02:30
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Lu,
You have argued this and said this many times before:

"Ask the following: Since the Robinson helicopters are restricted from sideslip and out-of-trim flight can the R22 and R44 meet the requirements of the Certification Requirements for Normal Category Rotorcraft which require demonstration of both to include 90-degree sideslip and 10-degree out of trim."

Consider also that helicopters (as well as other aicraft) are restricted from flying faster than Vne, yet there are several regulations that require flight testing (and thus demonstrating that such is doable) beyond this limiting speed (ie 27.143(e)(2) for power-off controllability). Just because one is not allowed to operate regularly in a given condition doesn't mean that such flight it not demonstrable.

I don't have the energy anymore to debate your other points
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Old 1st Nov 2001, 02:31
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Two things: Firstly, anyone, no matter how experienced, will benefit from the Robinson Safety Course. I last did it with two high-time men, an Australian with 13,000 hours and a Brit with 12,000, and both told me they were taking a great deal away.
Secondly, number-crunching on single-engine helicopter accident statistics in the UK over the five year period 1995 to 2000 (soon to be published) has produced the following. R22 fatal accident rate: 1 per 115,213 hours. S300/H269 fatal rate: 1 per 30,939 hours. B206 fatal rate: 1 per 39,903 hours. MD500 fatal rate: 1 per 14,956 hours. AS350 rate: 1 per 62,741 hours. Considering the R22 did 46.46 percent of all civil single-engine flying in the UK during that period, and that a high proportion of that was in training details and by low-time pilots, I'm impressed.
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Old 1st Nov 2001, 03:00
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To: Kyrilian

"Ask the following: Since the Robinson helicopters are restricted from sideslip and out-of-trim flight can the R22 and R44 meet the requirements of the Certification Requirements for Normal Category Rotorcraft which require demonstration of both to include 90-degree sideslip and 10-degree out of trim."
Consider also that helicopters (as well as other aicraft) are restricted from flying faster than Vne, yet there are several regulations that require flight testing (and thus demonstrating that such is doable) beyond this limiting speed (i.e. 27.143(e)(2) for power-off controllability). Just because one is not allowed to operate regularly in a given condition doesn't mean that such flight it not demonstrable.

It is not that the Robinson helicopters are not capable of sideslip angles of 90-degrees and out of trim flight at 10-degrees it is that they are restricted from doing it because of inducing high flapping loads leading to mast bumping. You can operate any piece of machinery to the point that you exceed operational limits but you are inviting disaster.

My point was that if the Robinson helicopters have this restriction, and let’s say that Frank Robinson,placed them up for certification at this date and, he told the FAA that his helicopters could not meet the certification requirements of operating at sideslip angles of 90-degrees + - or, fly out of trim by a ten degree angle + -, the FAA would most likely not grant approval.

In light of the above, the question begs asking and that is if it was discovered in 1995 that sideslip and out of trim flight would result in extremely high flapping loads why wasn’t this discovered when the helicopter was demonstrating these maneuvers to gain certification?

Regarding your comment above, I do not believe that the certification documents specify a Vne for any type of aircraft. This is established by testing and possible computer analysis to determine the operational limits of the aircraft. Once established, it becomes a part of the operational manual.

[ 31 October 2001: Message edited by: Lu Zuckerman ]
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Old 1st Nov 2001, 03:15
  #40 (permalink)  

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To: T'aint natural

I would suggest that you go back to those statistics and determine how many Robinson helicopters lost their rotor and how many of the other accidents involved rotor loss or rotor incursion. In GB and Ireland there have been at least three in the last year. One in Scandinavia and two in the United States.

If a commercial aircraft had those same statistics the fleet would be grounded.

[ 31 October 2001: Message edited by: Lu Zuckerman ]
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