Helijet S76 loses 2 tail rotor blades in lightning strike, and lands safely

[lelebebbel]

https://bc.ctvnews.ca/helijet-damaged-by-freak-lightning-strike-between-vancouver-victoria-1.6615284

[SASless]

Those Pilots need to go buy a Lottery Ticket while there good luck is with them!

Well Done, excellent airmanship!

They deserve all the time off they want....with pay!

[Sir Korsky]

IIRC, a 76 lost a paddle in NYC many years ago and landed at one of the heliports safely. The crew sad they had an unusual vibration. Could believe it.

[Tickle]

Amazing! Glad they were able to continue and land safely with 12 passengers in the back and a helicopter with half a tail rotor left!

Wonder if manufacturers test for this.

[megan]

a 76 lost a paddle in NYC many years ago and landed at one of the heliports safely. The crew sad they had an unusual vibration. Could believe itA little different cause, started a 76 for its first flight of the day and had an unusual vibration, tarmac hand came to the door and said the the tail was bouncing up and down six inches, later told it was water in one of the tail rotor paddles.

[nomorehelosforme]

Is a situation like this taught/practiced in a Sim as part of regular training?

[MLHeliwrench]

Zoom in and look at the chunk bit out of the horizontal stab!!! It’s wild! How much more pitch would be needed? A power of two I suppose.

Perhaps a new C - - mod coming out

[malabo]

12 pax, full load (3-rows of 4, none of that candy-ass limited seating like offshore). Looks like a departing blade took a bite out of the horizontal stab. Over water, they flew past Victoria airport and landed at the Camel Point Heliport on one of their 1D helipads elevated from the water. Gutsy move to counter that near 100% torque in a hover with half a tailrotor. Maybe they didn't know the extent of the damage.

Not Helijet's first lightning strike with a 76, last one left spot welds on a bunch of dynamic components - but the tailrotor remained intact.

[megan]

Is a situation like this taught/practiced in a Sim as part of regular trainingThe long answer is no, as manufactures don't test for this sort of scenario (loss of blades) as far as I'm aware. Loss of tail rotor drive (tail rotor no longer rotating) and tail rotor control stuck at a fixed setting (low or high power, or some point in between) is.

[lelebebbel]

12 pax, full load (3-rows of 4, none of that candy-ass limited seating like offshore). Looks like a departing blade took a bite out of the horizontal stab. Over water, they flew past Victoria airport and landed at the Camel Point Heliport on one of their 1D helipads elevated from the water. Gutsy move to counter that near 100% torque in a hover with half a tailrotor. Maybe they didn't know the extent of the damage.

Not Helijet's first lightning strike with a 76, last one left spot welds on a bunch of dynamic components - but the tailrotor remained intact.

​​​​​​​I would think that they didn't know they were missing tail rotor blades, otherwise I can't imagine they would've chosen Camel Point. The reduction of tail rotor thrust may not have even been all that apparent until final approach.

[helispotter]

...How much more pitch would be needed? A power of two I suppose...

Yes, half the number of blades would require about twice the angle of attack on remaining blades to maintain same overall tail rotor thrust.

I wonder if both blades departed at 'same' time or whether the massive vibration of imbalance after one parting caused the opposite one to then also fail shortly afterwards due to overload?

Lucky for it to end so well.

[JagRigger]

https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/1080x593/trb_cf46f00293abb2c1242997ae59827b4112e025bc.png

[sandringham1]

Loss of TR blade/blades leaving whats left in the only configuration that retains some semblance of balance and function is unbelievable. Very lucky people.

[Special 25]

Something similar to a Super Puma in the North Sea 30 years ago. 2 main rotor blades each lost part of their structure following a lightning strike and whilst there was a lot of vibration, the amount lost on both sides was fairly equal, so it stayed flying. Lightning works in mysterious ways - Maybe we should always have even numbers of main and tail rotor blades!

https://aviation-safety.net/wikibase/75393


Examination of the main rotor blades revealed that all four had suffered extensive damage and two diametrically opposite blade tips were badly damaged, each losing about 40% of their area

[fitliker]

https://www.lightningmaps.org/?lang=en#m=oss;t=3;s=0;o=0;b=;ts=0;y=46.8902;x=-121.7395;z=7;d=2;dl=2;dc=0;
Useful site for avoiding areas of lightning activity .

[helispotter]

In a separate thread re USAF AW-139s on 30th Sep 2018 SASless had written: "I know some OH-6A'S flew with half the blades gone from the rotor head....it was a dire emergency but it worked". I was keen to understand more about such cases. This S76 incident reminded me of the comment by SASless once again.

[212man]

I would think that they didn't know they were missing tail rotor blades, otherwise I can't imagine they would've chosen Camel Point. The reduction of tail rotor thrust may not have even been all that apparent until final approach.
Yes, I think we can assume that they would have diverted to an airport if they'd had any clue.

There was an AS365 (Aero Contractors) in Nigeria that had a loud bang after departing from a riverside helipad (Agip's Brass Terminal). They misdiagnosed it and shut and engine down then returned and lost control on short final, bounced off the pad and into the river - because the actual failure was a fenestron blade detaching, and the rest of the blades then shredding themselves on the shroud. Can't recall the fatality count, but included both crew.

[JokersWildMk.2]

Speaks volumes as to the robustness of the S76 tail rotor design if, as has already been observed, the crew had no reason to think they'd lost any tail rotor authority. To make matters worse, one wonders if one/both AP's remained ON after the lightning strike. Be bad enough losing a couple of blades at the back end, wouldn't imagine it'd be any fun having both AP's drop at cruise speed.

[MLHeliwrench]

Speaks volumes as to the robustness of the S76 tail rotor design if, as has already been observed, the crew had no reason to think they'd lost any tail rotor authority. To make matters worse, one wonders if one/both AP's remained ON after the lightning strike. Be bad enough losing a couple of blades at the back end, wouldn't imagine it'd be any fun having both AP's drop at cruise speed.

so it turns out a friend of a friend was onboard. There was a loud crack/bang and the helicopter rolled to the side/pitched down violently. (A passengers version of violently may differ from crew mind you.) I speculate that when the instruments went blank from the lightning they lost all AP.

it was apparently quite startling and ‘he legit thought he was going to die’ for a few moments. Once they descended and levelled off - everything was relatively normal. No alarming vibration levels he said. He and the other pax calmed down and the 8-10 mins of the rest of the flight seemed OK. There was a holy **** moment on the ground once everyone realized the condition of the tail.

[lelebebbel]

The 212 I was just flying got hit by lightning a few years ago, also in a tail rotor blade. The current traveled through the aircraft and down the attached 150ft long line, into the pond he was dipping out of.
The tail rotor stayed on with a tiny burn hole, but according to the pilot, pretty much every circuit breaker popped on the overhead panel, and he got a false engine fire light. Interesting how completely different the effects of lightning can be.

[212man]

wouldn't imagine it'd be any fun having both AP's drop at cruise speed.

Yes indeed. There are some here who will dismiss the issue of no AP, and will lax lyrical about flying the 76 without any AFCS in the early days, and it can of course be done without too much difficulty, starting from the hover and progressively accelerating and gaining the feel etc. However, to my mind, the stability characteristics are such that if you suddenly lose stabilisation unexpectedly at 145 kts I think it would be quite an unpleasant experience and would need real skill to get back under control. It would certainly immediately depart from straight and level flight in a big way (as described by the pax).

Edited to add that I just heard from a friend that works there and he said: "They initially lost all EFIS and both AP while IMC. UA recovery"

I would say that the account from the pax was entirely accurate! That would have been a horrible few moments.....

[SASless]

If one was sat their feet back, doing anything but being close to the controls and both AP's went on strike together at the same time.....yes there would be a diversion from straight and level no doubt.

If you were feet and hands on the controls when that happened.....yes....the diversion would occur.

How big the diversion would depend upon the reaction time of the Pilot "flying" the machine be it by buttons or by human appendages.

Add a complete and instantaneous loss of AP's and everything but standby/emergency instruments.....it would get interesting.

To be IMC when it happened....would be really interesting.

Add night time to it and Holy Mackerel Batman!

I recall the good old days when Air Log sent their brand new 76A's offshore to earn revenue until they could be sent for installation of the Sperry Kit....and those were not good ol' days.

I also recall a Bell 212 Operator that did not think SAS/AP were needed for night offshore flying citing "But, Gee....it is VMC weather minimums we are using.". Never mind the absence of surface lighting or horizon.

This 76 Crew rose to the occasion and did an excellent job and deserve accolades for their performance under what must have been very stressful conditions.

[Bksmithca]

The 212 I was just flying got hit by lightning a few years ago, also in a tail rotor blade. The current traveled through the aircraft and down the attached 150ft long line, into the pond he was dipping out of.
The tail rotor stayed on with a tiny burn hole, but according to the pilot, pretty much every circuit breaker popped on the overhead panel, and he got a false engine fire light. Interesting how completely different the effects of lightning can be.
with the long line in the water he was basicly ground so the lightning bolt took the path of least resistance

[Nescafe]

​​​​so the lightning bolt took the path of least resistance​​​

Not unlike most pilots.

[Uplinker]

Presumably the strike just happened to travel down one blade and out along the diametrically opposite blade,?, "releasing" both, and leaving a more or less balanced two blade rotor.

Very lucky, and very well done the pilots. Helicopters are scary things, mechanically speaking.

[Cyclic Hotline]

The S76 tail rotor assembly consists of two paddles attached to the Tail Gearbox, each paddle assembly consisting of a common spar with two blades attached to it - none of which can be disassembled in the course of normal operation and maintenance. It will be very interesting to understand the failure mode in this incident.

https://upload.wikimedia.org/wikipedia/commons/c/ce/S76_rotor_de_cola.jpg

[Mast Bumper]

If one was sat their feet back, doing anything but being close to the controls and both AP's went on strike together at the same time.....yes there would be a diversion from straight and level no doubt.

If you were feet and hands on the controls when that happened.....yes....the diversion would occur.

How big the diversion would depend upon the reaction time of the Pilot "flying" the machine be it by buttons or by human appendages.

Add a complete and instantaneous loss of AP's and everything but standby/emergency instruments.....it would get interesting.

To be IMC when it happened....would be really interesting.

if memory serves me right, there was a S-76 (a C+, I think) operated by AMEX, or GE, or IBM in the Northeast that suffered a dual generator failure while in IMC conditions - it took all they had to recover and continue flight. Things get VERY sporty without APs while in the clouds...

[Uplinker]

Wow, I had no idea that graphite was so strong in tension or resilient to vibration - I thought it was a soft material and not very mechanically strong at all.

But graphite, being made of carbon, might behave as an electrical resistor if a very large current from a lightening strike travelled through it. If so; its resistance to current flow would have made it get very very hot and disintegrate.

[albatross]

Wow, I had no idea that graphite was so strong in tension or resilient to vibration - I thought it was a soft material and not very mechanically strong at all.

But graphite, being made of carbon, might behave as an electrical resistor if a very large current from a lightening strike travelled through it. If so; its resistance to current flow would have made it get very very hot and disintegrate.

Wait for it…..someone will show up claiming that graphite was chosen specifically with this scenario in mind in order to create a “weak link” to ensure separation of the spar and both blades at the hub in the event of a lightning strike. Clever, forward looking those designer folk!

[60FltMech]

Graphite does some interesting things when struck by lightning. When I worked on AH-64D Apaches years ago a thunderstorm came across the field one night and an aircraft in parking suffered a strike to the VHF whip antenna at the top of the tail pylon.

This antenna is half aluminum and half graphite, the lower aluminum half exploded with enough force to cause puncture damage to the skin on the two tail rotor blades that happened to be aligned with the antenna.

The graphite portion, normally approximately 2 feet long and maybe 5/16” diameter, resembled a horses tail, all the fibers had separated into their individual strands.

The stabilator and tail pylon had to be removed for repair because of extensive additional structural damage(including sheared rivets and distortion in secondary structures), and the tail landing gear drag beam bushings were also damaged as the lightning traveled through to the ground wire on the tail gear.

Both the tail rotor and intermediate gearboxes were replaced as well.

Quite impressive.

FltMech

[helispotter]

Thanks for the illustration Cyclic Hotline. Hard to otherwise understand the 'innards' when seen from the outside.

Below are close-ups of the damaged tail rotor as seen in the TV footage. The 'paddle' with pair of blades that was on the side closer to the tail boom was the one that failed. There is no obvious sign of the graphite spar left sticking out of either side of the 'rubber boots' still on the inboard side of where the blades had been. So perhaps their graphite spar failed at the point where the pitch control rod passes through it? Either that or the spar failed in two locations either side of the pitch control rod but inboard of those 'boots' (which seems less probable?). If the spar or rotor attachment had fail further out, then I might have expected the unbalanced remaining blade and spar would shear off the pitch control link when they parted. Clearly, that didn't happen and the pilots presumably still had control of tail rotor pitch (for the remaining blades).

From the TV footage, it seems one of the remaining blades was also damage at leading edge near its attachment lugs(?):

https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/1287x513/sikorsky_s_76_helijet_damaged_tail_rotor_2_2e9279a858c4f3e4c 14c9e40e80852be52eb0046.jpg

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/841x539/sikorsky_s_76_helijet_damaged_tail_rotor_3_af9b1ad4d140894ab d7143004c6c1f167fccba7c.jpg

Here is a photo of an intact S-76 tail rotor including cropped to just its hub assembly:

https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/1726x1190/sikorsky_s_76_tail_rotor_hub_on_lloyds_raaf_example_8d02b26d a3d629162f53ff0f1909843fede57a9a.jpg

https://cimg1.ibsrv.net/gimg/pprune.org-vbulletin/693x581/sikorsky_s_76_tail_rotor_hub_on_lloyds_raaf_example_cropped_ e2d08ecbebc0e84754132c098bd7cffbd0a403ba.jpg

[60FltMech]

After seeing these pictures, I’ll throw out my theory of what happened, as I think it would best explain, considering the construction of the tail rotor system, how both blades could depart the aircraft simultaneously.

The s-76 tail rotor appears to be a smaller version of the UH-60, which uses an inboard and outboard retention plate to hold (and drive) the tail rotor paddles. There is an amount of clamping force that is checked with shims when installing the paddles and torquing the plates together, but that clamping force alone wouldn’t be sufficient to contain the blades from departing the aircraft.

As you can see from the schematic, the (graphite? Fiberglass? I forget) paddle spar has a hole in it that contains an oval shaped aluminum plug, with a hole in it for the pitch change shaft to go through, bonded into the spar(conveniently called a spar plug). The inner paddle is slid over the pitch change shaft and set into a recess in the inboard retention plate, then the outer paddle is placed over the inner one and recesses into the outboard retention plate.

I suspect the paddle failed at the spar plug area, as the spar is thinnest at the point either side of the plug. As the clamping force alone isn’t sufficient to contain the paddles, the now separated spar with blades attached overcame the clamping force and simply “slid” out from between the retention plate because of the massive rotational force. Pitch links probably didn’t even slow them down.

The only thing that makes me somewhat puzzled and could throw a wrench in my theory is the rubber boots shown still attached. On UH-60 these boots are bonded with Proseal to a piece of composite material that is in turn bonded to the spar at the inboard(retention plate side).

These are not structural parts of the paddle, just something to seal up the end of the blade root area to keep water
and debris out. I have seen these become disbonded from the spar before and they tend to tend to try to slide outboard towards the blade tip but they can only go a couple of inches.

The other end(blade side) is secured with a zip tie. So if the spar failed like I described the boots should have departed with the severed halves, unless the S-76 has a different attachment method?

I’d LOVE to watch the tear down of this assembly!🤣 As usual, Guess we will all have to wait for the investigation to see what really happened. ☹️

FltMech

[helispotter]

...if the spar failed like I described the boots should have departed with the severed halves, unless the S-76 has a different attachment method?..
.
FltMech

This short video seems to indicate on S-76 both ends of the 'boots' may be secured with zip ties:

https://youtu.be/ziQrzpxN614?si=fNXLOd_avaIZHSgh

[60FltMech]

Here’s what the H-60 paddle spar plug area looks like for anyone who’s interested:
https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/2000x976/img_3511_56e43fcfc713d28e2ecf508bcb65918f33a7b1c6.jpeg




And the outboard retention plate(pictured from underneath):
https://cimg8.ibsrv.net/gimg/pprune.org-vbulletin/1500x2000/img_3515_05b865cd797dc2b789a97a05c1d32f4035f5be6c.jpeg

And in my last post I mentioned the zip ties, they are on both ends on UH-60, but they are also Prosealed on the side closest to the retention plate.

FltMech

[albatross]

Having suffered through an idiotic, self induced total loss of AFCS in IMC cruise at night in a 76 I can say that, even with a full panel in front of us, it was a interesting and scary minute until we fully regained control. Far and away one of the stupidest things I ever did in a helicopter. Many lessons relearned that night. Came close to having an accident report with “Albatross was an idiot” as the only cause.

The crew in this event, made much worse by the loss of primary flight instruments, did an excellent job! Kudos to them.

Some folks on another site started criticizing their handling of events in the first comments before any details came to light.

It must be nice to be a “perfect pilot” and judge others from afar.

[wrench1]

The other end(blade side) is secured with a zip tie. So if the spar failed like I described the boots should have departed with the severed halves, unless the S-76 has a different attachment method?

Both ends of the boot have ty-wraps. The hub side has a better grip than the blade side so plausible the boots remained with the hub. There is a repetitive inspection that requires removing the ty-wraps and pulling the boot back.

Also think the spar fractured somewhere in the middle to get this result. Anywhere else and only one blade would have left plus the gearbox.

[Droopy]

Do they have triggered lightning forecasts in that area?