Accident To Sikorsky S61n, G-bbhm, At Poole, Dorset On 15 July 2002

[outhouse]

ACCIDENT TO SIKORSKY S61N, G-BBHM, AT POOLE, DORSET ON 15 JULY 2002
(HELICOPTER FORCE LANDED AND BURNT OUT AFTER ENGINE FIRE WARNINGS)

With little more to doooo just now I have been drifting through some of the Threads in the back pages. The one “Engine fire in flight question” by flying shrink, looked interesting so looking for a good read, followed the thread and found the comments by Spacer and the link to the CAA regarding the follow up report on the above S61N emergency.
I found the report informative and unfortunately it seemed familiar and almost a re-run of an incidence that occurred to a then British International S 61 back in the early/mid 1990’s. This was caused by a similar failure in the No5 Bearing, oil seal leaking oil into the aft support tube and torching from the high speed shaft (engine shut down). The fire was in fact a MGB fire ignited by the torching engine oil and subsequently the second engine showed a fire warning. The crew did an exemplary job, there followed water landing and evacuation to the comfort of a rubber raft and safe pick up. The 61 continued to burn and was destroyed down to the cabin floor pan. After sinking she was recovered and the AIB carried out an investigation and produced findings.

I had since felt that with the introduction of an integrated FR and HUMS system monitoring and trending transmission and engine vibration levels and in this case now monitoring turbine and high speed shaft frequencies that a repeat of the earlier incidence was extremely unlightly. Seems not in this case.

History will repeat it’s self if actions or recommendations that are specifically placed to prevent similar occurrences get lost in the mist of time, thus leaving the barn door open and the chance for some one else to get bitten in the posterior.

It may sound like an old aviator rambling but felt the story was worth a post.

Outhouse.

[zalt]

outhouse

Go read the report on British International G-BIED. Turns out the problem had occured on military H-3s since the mid 60s on. You may also also how effective the recommendations were to that earlier accident.

[NickLappos]

The real lesson in these incidents is not fire at all. The aux lube system is the answer, and should be standard by now on all 61's. The bronze sleeve bearings at the xmsn input are the culprit, of course.

[500e]

Could you expand your reply please Nick.
Are you saying there could be outstanding ADs or there is\was a more fundamental problem,that in your opinion was\should have been covered ?.

Here are a couple of sites to get a picture of zalt& outhouses enquiry :suspect:
http://www.caaerg.org.uk/docs/33/factor200421.pdf

www.griffin-helicopters.co.uk/accidents.asp (http://www.griffin-helicopters.co.uk/accidents.asp)
appendix i.pdf (http://www.aaib.dft.gov.uk/cms_resources/Appendix%20I.pdf)

[zalt]

Nick

Your thinking of another catestrophic defect. This is how an engine bearing failure can cause a fire that bypasses the firewall and torch the main box.

[outhouse]

Thanks zalt for the reading advice and to Nick for the comments re the rather dubious and inherently failure prone White metal high speed input bearing.
To my knowledge all S61 machines are now fitted with the emergency lubrication system. (stay on the ground if not) Inherently this type of bearing requires a constant oil film to retain its integrity and even when initially engaging the rotor after engine start it was imperative that the ELS was used as a pre lube to the bearings.
The failure of the said bearing could occur within seconds of the lube being lost from the bearing. Seizure of the high speed input and shearing of the GB input HSS and the whole assembly exiting from the gear box, and that was during initial engagement after engine start. Extremely exiting and a relief I expect that it failed when it did.
As I expect Nick will confirm the engineers have a cunning way of monitoring the gear box condition. A sample of the MGB oil was sent to a Lab, I think it was every 50 hrs. They carried out SOAP analyses. This gave the PPM analyses of the metal partials in the oil. So an increase in Tin and Copper would indicate a white metal bearing under stress and if deemed excessive generate an inspection. I seem to recall increase in Magnesium indicated a possible bearing location problem in the casing and steel? Gear tooth meshing problems. Any way I am sure some expert engineer would be able to clarify but you see the basic idea.
Add to that the computer analysis of the harmonics of the rotating components available with the modern HUMS system and in theory you can, identify developing problems, start maintenance actions to investigate developing trends, and catch the nasty event before it develops into a in flight emergency.
So, the engineer’s tool box now contains new tools that if used to the best advantage and had been in use years ago may have prevented the historical “Catastrophic Events”

So going back to the thread subject, with the new tools available to the engineer and the finding from another similar failure, is the system working and if not why not.

To all still flying the old and faithful lady, she is a comfort,predictable and a delight, however as a lady will sometimes come back and show her independence. Most from the early days are now enjoying retirement and the experience gained is lost to the new blood. (Except I suspect from old PPrune viewers)
Good luck and enjoy, I know I did then.

Outhouse.