"North Sea lelicopter crash causes revealed"

[Genghis the Engineer]

- is the title of a short article in the 14 August issue of Professional Engineering magazine. I've extracted a few bits, which may interest people here...

On 16 July, a Sikorsky S-76, owned by Bristow was ferrying oil workers between installations in the Shell field when it crashed 28 miles NE of Cromer. The wreckage was recovered and has been under investigation.

Upon inspection, it was noticed that one of the four rotor blades had a fracture, not consistent with the crash. Additionally, the casing of the main rotor gearbox had fractured and the gearbox and rotor head had broken away from the fuselage mountings in flight.

Analysis by research company Qinetiq on the blade indicated that it fractured due to fatigue before the outer portion separated. From this, it was clear that the blade fracture had initiated the event; the gearbox had separated from the fuselage mountings due to the severe imbalance created by the loss of the separated blade section.

Microscopic investigation of the fatigue point hinted that it had suffered intense thermal damage in the past..... It was ascertained that the rotor blade was struck by lightning in 1999 while fitted to another helicopter, thereby causing the damage.

Sikorsky has agreed with the AAIB findings and has removed from service any main rotor blade identified as having been damaged by lightning. Appropriate action has been taken by both the FAA and CAA.


G

[SASless]

Major question to me is whether Sikorsky inspected/repaired the subject blade and returned it to Bristow as "serviceable" and thus liability would fall on the manufacturer.......or was the blade either not sent to Sikorsky and/or the blade was returned without being certified as being "serviceable" by Sikorsky which would mean liability would then fall upon Bristow.

The real question is why an operator would want to continue using main rotor blades (a somewhat important part of a helicopter) after being struck by lightning. Particularly after the amount of damage aircraft G-BF incurred as a result of the lightning strike incident. Any reasonable person, having read of the damage and the number of components scrapped after the strike......would have serious misgivings about continuing to use the main rotor blades.

I cannot wait to hear how the liability issue is resolved.......it is very plain that someone will carry the bucket on this one. Reckon there is any finger pointing going on between Bristow and Sikorsky regarding this ?

One would think Sikorsky's smart move would have been to sell Bristow four new blades and refuse to certify the subject blades for continued flight.

I wonder if Bristow provided Sikorsky with a complete description of the damage to the aircraft as background information upon which to consider the inspections that would be required.

I can bet you doughnuts to dog droppings, you hold the stakes in your mouth, that Sikorsky just got out of the lightning strike inspection business for rotor blades!

[Capn Notarious]

With as few words as possible

Tell me how a Helicopter pilot knows: 1)That his blades
have been struck by lightening. 2)The immediate effect on
the flying characteristics. 3) Avionics. 4) Engine management.

[redandwhite]

For the info of the above:

You know when you've had a lightning strike from the incredible flash and an incredibly loud bang!!:eek: I was zapped in a 332 some time back and it made my co-jo drop his bacon roll! Luckily it was classified as a 'minor' strike, as the flight characteristics did not change, nor were any handling problems encountered. The only avioninc problem we encoutered was that the No.1 VHF went to permanent 'test' and stuck there, so we lived with the squelch for a while. Engine management was not affected.

I know of some other drivers that weren't so lucky with the severity of the strike, and severe vibration ensued. One could say they were lucky to have controlled the aircraft to a safe landing.

BTW, Eurocopter scrapped all four main blades in our case, even though only two showed signs of damage. Either they think differently to Sikorsky with regard to blades being returned after a belt, or they DO make sure their profits stay up!! :confused:

[S76Heavy]

Apparently, there is no way of NOT knowing when you've been hit by lightning, at least so I'm told. I don't know if it's clear WHERE the strike happened, but it certainly does a lot of damage to the electrics. Just read the AAIB reports on A/C that suffered lightning strikes.

I'm convinced that the affected blades had been sent back for a check and came back servicable for further ops. Why reuse the blade? Because parts are expensive, blades in short supply, and if the company who checked them says they're ok, they won't be scrapped on a hunch. That will have changed by now, I hope.

It will be interesting to see where the blame will be found and who will pay for the damages. 11 men paid the price..
:(

[Flight Safety]

FWIW, when the FAA issued the Emergency AD to remove all S76 main rotor blades in service that had previously been struck by lightning, they listed 8 total rotor blades by serial number. So, obviously they (Sikorsky) knew which rotor blades had previously been struck by lighting AND were still currently in service.

[ditchy]

I've been hit three times in helicopters. Once the lightning came in the tail and went out a blade tip taking the blade tip cover with it.

On a later strike, the lightning passed through the transmission. Within a few hours of flight time I had a chip light and the plug was totally covered in fuzz. The lightning magnetised the bearings which then began to disintegrate.

The last case showed no noticeable damage except burn holes in the skin. In all cases no electrical damage was done that I am aware of and I continued to operate these machines for weeks later.

Try and work out where the lightning came in and went out and you may have more idea of the damage.

If it passes through an engine or transmission be ready for the smallest sign of damage i.e.usually a chip light flashing as fuzz builds up. Engineers have told me the longest you can expect a magnetised engine to last is 20 hours.Maybe a transmission too.

I have had a strike go through an engine on a fixed wing which resulted in the engine being replaced. Interestingly, it also welded the fuel control unit rods solid and the engine could not be shut off using the cockpit fuel lever.

[Red Wine]

3 Times......!!

Remind me to call in sick if we are ever rostered together........

[Capn Notarious]

THANK YOU FOR REPLYING

[Genghis the Engineer]

Strikes me that the lesson here is not that you want to know if you've just been struck by lightning, but whether your blade was at some point in its youth.

G

[soggyboxers]

Not exactly a lightning strike, but many years ago I was flying a Bell 212, IMC, offshore at night and there were numerous Cb around with quite a bit of electrical activity obvious nearby. A fairly small blue ball of (what I presume was) St Elmo's fire formed around the tip of the Spillsbury Tindall HF antenna a few feet ahead of the radome and disappeared after a few seconds. Shortly after that the radar started spiking, then there was quite a large bang as all the electrical CBs popped! I didn't think it was probably a very good idea to start resetting anything at that stage, especially as one of the overhead CB panels had also opened and was just swinging on its hinges. Luckily, the standby horizon was working, the E2B compass appeared unaffected and as all the pressure instruments were okay we eventually managed to get into VMC conditions and find our way back whence we came onshore. An interesting evening though!
After inspection it appeared that a couple of large diodes had blown, but the rest of the aircraft was unaffected.