1986 UK Chinook Disaster Mini-Documentary
 

Saw this new video come up on YouTube yesterday:



I had never heard of this accident before, pretty shocking. Did this discourage more civilian operators from using Chinooks?

Watched a Vertol heli-logging in BC . The machine once flew in the North Sea . Columbia helicopters had been operating it safely without incident for thousands of hours . Their secret ? The first thing they did when they got it was switch out the gear boxes for the military version gearbox . And voila a safe hard working machine . That was twenty five years ago not sure if it is still heli logging today . They said they did not like the fancy civilian gearbox and the military version was better suited to their requirements. Who knew a gearbox is so important ?

Accident report

https://assets.digital.cabinet-offic...988_G-BWFC.pdf

Yes, killed it's use stone dead in the North Sea ISTR. Amazing that anyone survived the crash.

The report doesn't indicate the existence of a 'Military Gearbox', only different modification standards, the change to -6 being the important one in the accident report.

Assumption that modifying the nature of the mating surfaces would not change wear patterns at those surfaces was an error. Underestimation of the acceleration of corrosion due to salt laden air was also a big factor it seems.

Yeah right......Accident Boeing CH-47C Chinook 74-22292, 11 Sep 1982 (aviation-safety.net)

On BBC iPlayer and still available for about the next month, the G-BWFC accident is revisited in Series 1 Episode 2 of "The Disasters That Shocked Scotland". The BBC progamme is focused less on on the technical aspects, but rather more on the personal accounts of the two survivors, one of whom was the Chinook's captain.

bbc.co.uk/iplayer/episode/m000xs2y

Interesting read. Has any study been made on the effect HUMS has had on aircraft safety ?

Much like the Super Puma, this was the last straw after a number of incidents (including ditchings) and a general dislike of travelling in it.

It was the direct catalyst for the development of HUMS, sponsored by Shell (the client), Bristow and Plessey

Spot the CH-46 Sea Knight in there!

Interesting that they show G-BKZE (Super Puma) at then end - that was the one that rolled over on the West Navion in 2001.

I remember when they sent civilian contractors to do an inspection on the entire US Army CH-47C fleet, one of the things they were checking was torque on the spiral bevel gear bolts - my ship failed, quite a few were loose. Had to replace the aft transmission...

The crash referenced by 212man was a different cause though, related to using walnut shell media blasting during the transmission overhaul process - oil passages were being left plugged when things weren't cleaned out properly.

Helicopters are unforgiving of maintenance errors, some more than others.

Funny - I was looking through the UK AAIB report for a reference to that as I recalled reading it. Obviously I saw it in a report on the US accident. Memory is going!

Walnut shells...

As I recall, the walnut shells were used to clean the gearbox internal surfaces and oil ways and blasting out any residual shell particles using high pressure air/nitrogen had worked a treat for many years.

That is until Health and Safety got involved and called into question the safety case of using high pressure blasting as a maintenance procedure, so the gas pressure used to purge the casing and oil ways was reduced, the outcome of which was that residual shell fragments remained lodged in oil ways and this was not picked up prior to MGB rebuild.

Loss of torque...

I have lived several lifetimes since my Chinook days' at Odipus, but as I recall, at the time Boeing issued an alert bulletin to check the FWD MGB Spiral Bevel Ring Gear retaining bolts for loss of torque loading every 25 flights hours.

As noted, it was a long time ago, but I believe the engineering concern at the time was the minimum safe edge distance from the centre of the attachment bolt holes to the edge of the ring gear, as such it was not considered safe to open up the holes and install larger diameter bolts.

A pain in the butt as it was, Crab Air was happy to wait for Boeing to identify a fix that that they were happy to have installed on MoD gearboxes, but not so for the NS Commercial World. As such an engineering solution was expedited between Boeing, the FAA and UK CAA that resulted in tapered bolts being installed that could accept higher torque loadings, but clearly the modification process produced its own problems.

History can be an interesting aid to the corporate memory.

The reference to technology we know as Hums and how it was thought such innovation could prove very useful in preventing accidents reminded me of seeing the trials work being done while flying on the North Sea.

Am I right to assume that technology was mature and installed on the two aircraft that shucked their rotor heads following a main gearbox failure?

In the Chinook crash....there was no such system installed and the Crew had only their human senses to monitor the aircraft vibration/noise levels.

The problem with that is in the case of a sudden onset ....there is scant time to react.....and for a long slow gradual onset you might not pick up the change as you get used to the existing level thinking it is normal.

Durig. my time on the Chinook....all in military versions....our Flight Engineer and/or Crew Chief would make frequent vibration checks using a finger nail or knuckle and odd as it sound (poor choice of word that) sometimes they could pick up an unusual vibration in parts of the airframe.

Now that we do have vibration sensing systems....the problem that has to be dealt with. is having the ability to determine what is a vibration or change in vibration that we should be concerned about.

The rub....is not every potentially catastrophic gear box failure will give a lot of advance warning.

When you consider how complex the design, engineering, and construction of a gearbox is.....it is not surprising that unforeseen problems occur.

The Chinook is no different than any other helicopter in that regard as history reminds us.

I was at the Sikorsky factory when the 76 was wining the Rotor Blade tossing contests and that too came from an unforeseen stress point. on the threaded portion of the blade retention system.

https://www.colheli.com
Looks like they are still flying them .

I presume that the spiral bevel gear assembly now comes in a one-piece milling instead of a two-piece bolted assembly for modern Chinook gearboxes?

Yes, but HUMS doesn't work on epicyclic planet gears, the technology to make that work doesn't, or didn't, exist. That is why epicyclic chip detectors were fitted. But HUMS was pretty good at other types of gears. Just because HUMS is not perfect and doesn't trap 100% of failures, doesn't mean it isn't a very good thing. A corollary would be that clearly pilot training doesn't work 100% effectively because there are still pilot error crashes. Therefore what is the point of having any pilot training?

HC.....thank you for confirming what I said....so perhaps what you missed is I was noting that exactly as stated in the Accident Report...new designs might not work as anticipated and that would include systems like Hums and similar technology and we should be very careful our consideration of their effectiveness.

I am old enough to remember rotor track and balance being done with a pole and flag and some grease pencils and lived long enough to see the Chadwick system come along and change the standard for the better.

Same for. Hums....I saw the old bent knuckle advance to the state of the art systems we enjoy today.

That being said....just as your comment reminds us there is a limit to every system's ability to give advance warning of failures.

But as in your example....the chip detector system had to be altered and improved didn't it?

Did Eurocopterr ever come out with the exact cause of the failures....the actual root cause?

I recall they were being a bit quiet about it despite stating they had it figured out and fixed.

I know it was a sad day for you when those Cabs got hauled off for use as potting sheds.

I felt the same when that happened to the Chinook on the North Sea.

The only good of that was Columbia got some darn good helicopters cheap and. have flown them since and made a lot of money tn the process.

Forecasts are the Chinook design shall be flying well over a hundred years after coming to service with the US Military.

Chinook is alive and well in the US Army. Like the C-130, good solid design.

I believe HUMS data stopped the rather punchy RAF Chinook display.

Not strictly HUMS, but an enhanced data recorder package that was fitted to a selection of aircraft. Some rather wince-inducing numbers came back, and subsequent investigation of the stresses that had been put on the blades was even more eye watering.... Health and safety gone mad it was definitely not!

Shame, it was a very good display but you can't argue with the data.:ok:

I displayed the Lynx at Cosford this year and I'm sure people were disappointed that there were no backflips, loops and rolls but you just can't do that stuff any more - the Blue Eagles Lynx had G meters and in the F700 all the manouevres were recorded , each of which reduce component life significantly.

A private owner can't afford to do that and the permit to fly wouldn't allow it anyway.

was that XZ179?

No, XZ 616 from Historic Helicopters, the first Lynx back on permit to fly :ok:

Nice one, Crab. :ok:

Slapping the tail rotor blades against the tail pylon stopped the Puma display!

My point was that HUMS was never expected to identify planet gear flaws, it was not designed into the system. Which is a bit different from expecting it to work and then finding out the hard way that it didn’t.