AS 350 down (9 April 2018)

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Re: AS 350 down (9 April 2018)

Unread postby Keith Quixley » Tue Apr 10, 2018 11:18 pm

carenkok wrote:The investigation is on going and the owner and myselve are in constant contact with no issues and/or finger pointing. It is a very sad accident as HHI has been a child of mine for 6yrs threw Ebola in Liberia where she has been operating until mid last year and many sweat drops, Gin and Tonics all over Liberia, too much to mention. Great times! She looked stunning in her new config!

We await the outcome but hope I never see 1 of my customers so critical of our efforts as AME and a AMO.

A Gin on HHI!


Is dit Anel se sussie?
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Re: AS 350 down (9 April 2018)

Unread postby carenkok » Tue Apr 10, 2018 11:34 pm

Anel du toit? Indien ja-oops! Lol
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Re: AS 350 down (9 April 2018)

Unread postby Walter105 » Wed Apr 11, 2018 6:18 am

Would be interesting to know at least what the problems were that presented themselves and ended up with the broken helicopter. Did the engine stop? Did the tailrotor fail? What is known so far?
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Re: AS 350 down (9 April 2018)

Unread postby hugo_visser » Wed Apr 11, 2018 8:35 am

Well this helicopter is from the Alouette family, they just do not break, they always give you a warning if you are fine tuned to the machine, so it was at Tempe, assume refuel, and just out of AMO, so loose debree in tank coming loose maybe, and clogging a filter. I do not know the systems very good but should have a filter bypass, dirty fuel is better than no fuel, and will give you time to find a landing spot. This has happened to me once when refilling at Standerton fueling depo. Always carry a spare filter with me. Same on the Hydraulic standpipe in 737 system, dirty hydraulic fluid is better than no hydraulic fluid for a short period to maybe extend flaps and landing gear.

Guys please remember, you do not have to get home, I will come and fetch you, have a trailer just for that, 24/7

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Re: AS 350 down (9 April 2018)

Unread postby Mr Mieleis » Wed Apr 11, 2018 4:36 pm

Hover and then LTE

Loss of tail-rotor effectiveness (LTE) occurs when the tail rotor of a helicopter is exposed to wind forces that prevent it from carrying out its function—that of cancelling the torque of the engine and transmission. Any low-airspeed high-power environment provides an opportunity for it to occur.
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Re: AS 350 down (9 April 2018)

Unread postby hugo_visser » Thu Apr 12, 2018 5:17 pm

How would one recover? Fundis help please, I like to learn all the time. I would, low to the ground, pull more collective, that would spin you more to the left and corkscrew up, even press a little left rudder to unload the tail rotor, and corkscrew faster, once high push cyclic forward lower a little collective and slight right pedal and fly away. This machine would want to swing to the left due to main rotor rotation. Higher up from the ground, lower collective, cyclic forward and fly it away, if you can, light left rudder to turn left and unload tail rotor, flying away in a left turn. ???

Easy now in afterthought, with lots of time on hand, This happens super fast.

What say the experts ?

Hugo.
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Re: AS 350 down (9 April 2018)

Unread postby jimdavis » Thu Apr 12, 2018 6:00 pm

hugo_visser wrote:How would one recover? Fundis help please, I like to learn all the time. I would, low to the ground, pull more collective, that would spin you more to the left and corkscrew up, even press a little left rudder to unload the tail rotor, and corkscrew faster, once high push cyclic forward lower a little collective and slight right pedal and fly away. This machine would want to swing to the left due to main rotor rotation. Higher up from the ground, lower collective, cyclic forward and fly it away, if you can, light left rudder to turn left and unload tail rotor, flying away in a left turn. ???

Easy now in afterthought, with lots of time on hand, This happens super fast.

What say the experts ?

Hugo.


Hugo, that all sounds unbelievably complicated, but I am just wondering if you might get a bit or torque the other way by switching on the rotating beacon? :lol:

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Re: AS 350 down (9 April 2018)

Unread postby happyskipper » Thu Apr 12, 2018 6:15 pm

Loss of tail-rotor effectiveness
From Wikipedia, the free encyclopedia

Loss of tail-rotor effectiveness (LTE)[1] occurs when the tail rotor of a helicopter is exposed to wind forces that prevent it from carrying out its function—that of cancelling the torque of the engine and transmission. Any low-airspeed high-power environment provides an opportunity for it to occur.

Contents

1 Causes
2 Indications of onset
3 Recovery
4 See also
5 References

Causes

Environmental factors which can lead to LTE include higher operating-density altitudes or temperatures, and high winds. A high gross weight can also create an LTE-conducive situation. Causative wind-directions may include:

Main-rotor vortexes pushed into the tail rotor by wind. This can occur with wind coming from 10 o'clock on North American (counter-clockwise) rotors and from 2 o'clock on clockwise rotors. The wind pushes the dirty air and vortexes generated from the main-rotor into the tail-rotor, preventing the tail rotor from having clean air to propel.
Wind from the tail (6 o'clock) can cause the helicopter to attempt to weathervane into the wind. The winds passing on both sides of the tail rotor make it teeter between being effective (providing thrust) and ineffective (not providing thrust). This creates a lot of pedal work for the pilot to eliminate unintended yaw.
Wind moving in the same direction as the tail rotor moves air. With pusher tail-rotors, that is wind from the opposite side of the tail-rotor. With puller tail-rotors, that is wind from the same side as the tail rotor. For main rotors with clockwise rotation (European), that is wind from 9 o'clock. For main rotors with counter-clockwise rotation, that is wind from 3 o'clock. The wind going through the tail rotor causes an actual stall condition as it decreases the effective airspeed of the air through the tail rotor. This condition will cause an unintended yaw that may develop into a spin. Recovery from this condition may be difficult if no airspeed is available, and will require entry into an autorotation (thus removing the torque of the engine and transmission).




https://en.wikipedia.org/wiki/Loss_of_tail-rotor_effectiveness
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Re: AS 350 down (9 April 2018)

Unread postby matt8 » Thu Apr 12, 2018 7:15 pm

If this was LTE then it is pilot error.
The pilot makes certain choices and decision that puts a machine into the state and situation that leads to LTE.
It's always banded about as if it's unavoidable and "&%#^ happens" and it's no ones fault.
If you're experiencing LTE you are far behind your machine and your decisions put you in that predicament.

Hugo, LTE is an issue with not enough anti-torque produced to counter the amount of torque that the power plant puts out.
That could be due to a shortage of power or an airflow issue, again all avoidable.
Pulling collective is only going to make the matter worse by increasing the amount of torque generated.
Depending on your position, lowering collective will help - obviously depending on proximity to terraforma.

Here's 2 great examples. First one the guy has lots of height to be able to control the issue by reducing his power but doesn't. The second 1 he doesn't have much space, but you can see it heading that direction fairly early:



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Re: AS 350 down (9 April 2018)

Unread postby Tim » Fri Apr 13, 2018 9:55 pm

I am not so sure. In the in cockpit footage at the end of the second video, I can clearly hear rotor RPM going down. Maybe the pilot simply ran out of power in a tailwind transition.
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Re: AS 350 down (9 April 2018)

Unread postby Captain Kirk » Mon Apr 16, 2018 4:53 pm

For those interested, Buzz Bezuidenhout wrote this article on LTE a few years back which went up on Rotor & Wing's website.

He was doing demonstrations on this too, did it in one of my renewals with hm, scary stuff! :shock:

Around the World: Avoiding LTE
By By Buzz Bezuidenhout | October 1, 2011

Loss of tail rotor effectiveness (LTE) has been around for a long time and the majority of helicopter pilots are familiar with this aerodynamic phenomenon. They will have been briefed on it during basic training and have probably discussed it when fraternizing with their rotary wing colleagues.

Very few will actually have had it demonstrated to them during training and Heaven forbid, experienced it firsthand during their day-to-day operations.

Whenever a helicopter is maneuvered in close proximity to the surface, either in the hover or low speed forward flight, there exists the potential for development of this condition. The following is a brief description of LTE.

Causes:
• Weathercock instability downwind, i.e., the pilot has a high pedal workload with varying tail rotor thrust in order to prevent the helicopter weathercocking into wind—occurrence mainly in the hover.

• Left crosswind with anti-clockwise rotor system and vice versa, which could lead to development of a vortex ring state on the tail rotor with subsequent loss of thrust—occurrence either in the hover or in forward flight.

• Left quartering crosswind which entrains the main rotor disc vortex straight into the tail rotor with subsequent disruption of airflow on the tail rotor and loss of thrust—occurrence either in the hover or in forward flight.

Most Causative Factors:
Left quartering crosswind while terminating transition, particularly during steep, constant angle approaches. Left crosswind in either IGE/OGE hover.

Avoidance:
Sufficient IAS should be maintained when operating close to surface and not G/S—any uncommanded right yaw should be corrected immediately.

Recovery:
An increase in forward speed with a possible minor reduction of collective—the CP not to be lowered completely since this will create accelerated ROD and a rapid increase of CP to correct the ensuing increase in sink rate will drive the M/R straight back into vortex.

What is not mentioned in most publications is the fact that allowing rotation to develop will exacerbate the vortex ring situation on the tail rotor (I stand corrected here since initially the tail rotor will go from a vortex ring situation to a windmill brake state and thereafter a completely stalled condition if the rate of rotation is extreme enough).

This will rob the main rotor of rpm, resulting in a large loss of thrust and the aircraft settling, the pilot applying CP to correct this situation and the main rotor developing vortex ring, all of which will result in an accident—irrecoverable if the pilot is not aware of what is happening.

Caution should be exercised during operations close to the surface, i.e. hovering IGE/OGE, confined area inspections/approaches/game catch/cull operations/crop spraying/vehicle tracking, to mention a few.

If this occurs below 50 feet AGL it will result in a rapid, uncontrolled rotation with a hard landing at the very least; if it occurs between 250 and 150 feet AGL on approach it will result in a catastrophic accident.

I discovered these secondary effects the hard way. I was asked by a client to actually demonstrate the LTE condition and subsequently did so. The results as described above were frightening and all the helicopters on which I have subsequently demonstrated LTE have experienced a rapid development of vortex ring state on the main rotor in less than one rotation.

Therefore it must be understood that the onset of both vortex ring and LTE can be violent and rapid if conditions are right, giving the pilot very little warning and leaving extremely little chance of recovery, particularly if the pilot is not aware of what is happening. Keep in mind that this condition can occur on any helicopter with a conventional anti-torque system.

I have seen a training video at Bell that shows a Eurocopter Dauphin (Fenestron-type anti-torque system) suffering from this phenomenon and crashing in an uncontrollable fashion from low altitude. The client I mentioned suffered from this in that he was orbiting a confined area carrying out an inspection prior to landing—he maintained a constant G/S as opposed to IAS in a very strong wind during the orbit, found himself settling on D/W at low speed, rapidly applied CP to correct this, rotated out of control and developed vortex on the main rotor resulting in a serious accident from an altitude of 500 feet AGL.

Note: S.P. “Buzz” Bezuidenhout is a senior helicopter flight instructor and designated examiner based in Johannesburg, South Africa.

http://www.rotorandwing.com/2011/10/01/around-the-world-avoiding-lte/


Tim wrote:I am not so sure. In the in cockpit footage at the end of the second video, I can clearly hear rotor RPM going down. Maybe the pilot simply ran out of power in a tailwind transition.


Note the comment on losing RPM, third paragraph under the Recovery heading.
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Re: AS 350 down (9 April 2018)

Unread postby Backmarker » Mon Apr 16, 2018 7:23 pm

After reading the last page and more stuff about LTW I have new found respect for helo pilots. :shock:
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Re: AS 350 down (9 April 2018)

Unread postby tanglefoot » Mon Apr 16, 2018 9:02 pm

Backmarker wrote:After reading the last page and more stuff about LTW I have new found respect for helo pilots. :shock:

Shhhh, don't tell everyone.
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Re: AS 350 down (9 April 2018)

Unread postby jimdavis » Mon Apr 16, 2018 9:37 pm

tanglefoot wrote:
Backmarker wrote:After reading the last page and more stuff about LTW I have new found respect for helo pilots. :shock:

Shhhh, don't tell everyone.


Come on Tangles - you know he wasn't referring to you. 8-[ :lol:

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Re: AS 350 down (9 April 2018)

Unread postby tanglefoot » Mon Apr 16, 2018 10:09 pm

jimdavis wrote:
tanglefoot wrote:
Backmarker wrote:After reading the last page and more stuff about LTW I have new found respect for helo pilots. :shock:

Shhhh, don't tell everyone.

Come on Tangles - you know he wasn't referring to you. 8-[ :lol:
jim

Yes, I know that but he was probably referring to cage and that is even worse 8-[
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