CH47D Droop Stops Failure Procedures

[wingeu211]

Hi fellow flyers...
Greetings...anyone can advise what's a good procedure to adopt when you discover the aft droop stops of the CH47D are not in during shutdown?
I have heard about using planks and even mattress placed at the side of the helicopter to prevent the drooping blades from contacting the fuselage... any truth to this or can anyone provide your experienced advice?
thanks

Fish

[Rigga]

Late 80's - this happened during an exercise at RAF Odiham on a RAF Chinnok Mk1 (CH47-C). Aft Droop Stop found on the floor just after reaching full RRPM.

After many hours of theorising and trying to confirm exactly which was the errant Blade - it was decided to take the Hand-Rails off a "Giraffe" (Hydraulic lift/work platform with 20-25 feet of steel stairs leading to a work platform) secure some planks to form a smooth sloope and grease them up. the new Ramp was placed with cushioning, to the mid -Tunnel position Left side.

Crews practised the timing of the moving blades so that a call could be made as the errant blade was AFT of the ac giving time for the brake to start holding after the blade passed over the tunnel.

After approx 8 (yes eight?) hours of Ground Running - and now with an audience of several hundred people released from the exercise - a group of 4 or 5 crew were compressed into the tiny cockpit to get as many hands onto the Brake Lever. The RRPM was slowed to "as slow as as possible..." before the well-timed shout went to put the Brake on as fast as possible......
.
.
.
.
.
.
.
.
.
.
.
.
.
.
All went well!

and the Rotors stopped within 1.5 turns and the only damage I saw was the Aft Rotor's Lower Oil Tanks and Aft Crown Fairing were crushed and the Upper Anti-Coll Lamp was broken.

The errant Blade didn't touch the tunnel covers and no damage was done to any blades - the "Ramp" was not touched.

Hope this helps?

[Fareastdriver]

Why not use a fire hose like they used to use on the Bristol Sycamore? That had a problem if the droop stops did not engage as the blade, complete with 20mm. shaped mass balance, would punch holes in the boom.
The trick was to get the fire section to play a jet of water over the boom in the direction of the blade travel. On shutdown the blade would bounce (or surf) the jet and no harm would come to anything.
Apart from the blades; that were made of wood. They had to be taken off, dried out, and re-tracked in the tracking tower as a set.

[saudipc-9]

Happened to a Canadian Chinook in Afghanistan

Here's the link, it's worth a good read and the picture is what you are looking for.

CH147204 Chinook... | Rotary Wing | Reports - Investigation | DFS | Royal Canadian Air Force | DND/CF (http://www.airforce.forces.gc.ca/dfs-dsv/nr-sp/index-eng.asp?id=10000)

[Rigga]

Good find -PC9 - Better details of my poorly remembered story is in the incident report - Annex's F & G

[NutLoose]

Fareast driver, probably because it had come off, we used hoses on the Wessex and one time when that failed a rigger got on the platform lying down and after several attempts whacked it as it passed with a hide-faced hammer, it was like out takes from the Thor movie with hammers flying everywhere.... ahhhh health and safety would of had kittens...

[extpwron]

Just to add to Rigga’s story, I did one of the shifts at the controls during the 8 hours of ground running while the engineers came up with the solution.

Seem to remember one of the problems was getting advice from Boeing in the States due to the time zone difference - a number of them had to be woken!

I wasn’t part of the shutdown crew and recalling that on that very same dispersal several years earlier a Wessex thrashed itself to pieces during a ground resonance incident (cars damaged hundreds of metres away) - I watched this shutdown from a safe distance!

Engineers did a great job with minimal damage compared to the Canadian incident – can’t believe they didn’t have rotor brakes fitted though.

[Shackman]

I can tell you what it feels like from the front when they fail during shutdown - a lot of crashing and banging, sunroof modification carried out just aft of the cockpit right on the fire extinguisher relays (I think they have now been moved!), and in my case one blade finished embedded in the port fuel tanks. The crewman actually thought the aft pylon was failing, and ran to the front of the aircraft, just in time to see the blade mentioned above coming straight towards him. However, even though there was a fair bit of damage to the roof, all the pipework was still intact, hydraulics still on line (from the APU), and in subsequent inspection the drive shaft was still intact, straight but slightly dented, so the blades didn't desynchronise, which would have been considerably more catastrophic (thank you Mr Boeing).
(Photos will be added when I find them).

Incidentally I was also rung re the incident at Odiham but as mine had occurred 'in the field' there was little I could add to their ideas!

[Exrigger]

The 18 sqd one on the pan caused quite a bit of damage as the blades struck the tunnel covers/roof, but no one knew the droop stop had failed and fallen off post a heavy landing in a field.

During the Turkey operations post gulf 91 an american chinook landing near our tent accommodation with a rear droop stop stuck out and we utilised the fire hose approach which worked a treat, the 7 sqd guys also suggested the giraffe approach but that was not feasable where the aircraft was, don't think there was any giraffes either come to think of it.

[talking horse]

How would you know that the droop stop is not in before shutting down? RAF Chinooks have a droop stop shroud (a fibreglass cover) fitted over the centrifugal droop stop. It is there to prevent ice from preventing the droopstop from moving in on shutdown, and was an in-service modification towards the end of Chinook HC1 days (Mod 91 if memory serves! It was a requirement for flight in icing conditions.).

The incident referred to a Odiham with the 8 hours of ground running was triggered (I believe) when one of the groundcrew found the droopstop on the ground after start, and someone recognised it and its significance. This may have been before the days of the droopstop shroud modification.

The US one in Turkey probably didn't have shrouds fitted so the droopstop was visible. However, with the shroud in place, you can't see if the droopstop is in or out and a fire hose can't actually impact the offending item. So I suspect the first you might know of it is a big bang on shutdown!

As an aside, there was a similar event at MPA some years ago, although it was due to a blade root failure. I think the cause was water ingress to the material wrapped around the root of the blade which then froze. I saw the aircraft afterwards and most of the damage was to the upper edge of the forward fuselage, and I think the blade bounced off the fuselage and over the tunnel. ISTR the crew said that they then put the brake fully on, and the blades stopped in about 2 revolutions. Exciting stuff - the trip's not over til you're back in the crewroom!

[Exrigger]

TH you are correct if the shrouds are fittted, but we did not fit and forget the shrouds they were only fitted when deemed necessary.

The 18 Sqn incident the missing droop stop was not noticed because on shut down the LM does not check them like the americans used to i.e. he is inside monitoring the rotor brake for over heating/fire on shutdown and you are quite correct though in that if the shroud is fitted you cannot see the droop stops, the fire hose would not work and the first you would know is the big bang.

I was on top of an aircraft two down from the 18 Sqn one, doing independent checks prior to another rotortune flight and it shocked me, thankfully no-one was hurt.

[Corrona]

We were shown a video of the Odiham incident on EST. It was quite funny to see the Staish come tearing up in his Austin Princess (or some other such rubbish) along with a load of blunties to save the day. I seem to recall that an SAC liney suggested the Giraffe idea.

Someone must have a copy for us all to see?

[Fareastdriver]

you cannot see the droop stops, the fire hose would not work

The procedure I described with the Sycamore had nothing to do with forcing the droop stop back in. The stream of water was ensure that the blade did not come into contact with the rest of the aircraft on shutdown; it would ride the jet over the top.

[Exrigger]

That must have been more exacting to do that on a turning and slowing blade than a high pressure hose jet aimed under the hub to force the droop stop back in, as we did. I would not of liked trying that at night with a Chinook aft blade.

[NutLoose]

I wasn’t part of the shutdown crew and recalling that on that very same dispersal several years earlier a Wessex thrashed itself to pieces during a ground resonance incident (cars damaged hundreds of metres away) - I watched this shutdown from a safe distance!




Aahhhh, wasn't that a certain Wing Commander, who reputedly climbed over the other pilot to get out and also managed later to tear the tailskid out of the boom of a Puma and then tried to pin it on the Rigger that did the turnround prior to his flight?, so much so they had a Landy scouring the airfield looking for the impact point!

[SirToppamHat]

Not video as such, but some interesting photos and info here:

CH47 Droop-Stop Failures (http://www.chinook-helicopter.com/maintenance/issues/droop_stops/droop_stop.htm)

STH

[OafOrfUxAche]

what's a good procedure to adopt


Are you mid-shutdown as we speak? Take some more fuel and I'll get back to you in a bit...