A short history about Skydrol

[JammedStab]

From Aviation Week

Early aviation hydraulic systems were used to apply brake pressure. These systems used a vegetable oil-based hydraulic fluid. As aircraft design produced larger and faster aircraft, greater use of hydraulics was necessary.

These advances led to development of petroleum-based hydraulic fluids such as Mil-O-3580 and, later, Mil-H-5606. Shortly after World War II, the growing number of aircraft hydraulic fluid fires drew the collective concern of the commercial aviation industry and the public.

In 1948, Monsanto Company, Solutia’s former parent, worked with Douglas Aircraft Company to develop a fire-resistant hydraulic fluid based on phosphate ester chemistry, which was named Skydrol® 7000. As the transport industry moved toward jets, Skydrol® 500A fluid was developed to meet the environmental needs of the new aircraft, and with the continuous development of more advanced aircraft further modifications to Skydrol fluid formulations were made.

These changes, required by the aircraft manufacturers, are known as modifications to the fluid specification ... or simply as Type I, II, III, IV, and now Type V fluids. Skydrol® LD-4 and Skydrol® 500B-4 hydraulic fluids are Type IV fluids formulated to exceed the rigid specifications of the aircraft manufacturers. They have been in commercial usage since 1978 and have demonstrated outstanding performance. Skydrol 5 was our first Type V fluid, and now Skydrol PE-5, introduced in 2010, is our newest, longest lasting hydraulic fluid. In 1997, Solutia Inc. was formed from the Industrial Chemicals Division of Monsanto.

Eastman Chemical acquired Solutia and the Skydrol product line in 2012. Skydrol became part of the Eastman Aviation Solutions family of brands in 2014 combining the proven performance of Skydrol with SkyKleen and Eastman Turbo Oils to provide an industry leading fluids solution to the industry

[172_driver]

Obviously an essential part of an aircraft.

Another story about Skydrol; Pilot incapacitation as result of exposure to Skydrol fumes during turnaround. It was a tiny leak, the mist created was enough.

I would never enter a wheel well with hydraulics pressurized.

[JammedStab]

Thanks for the story. I do remember a situation on the 727 with a main deck cargo door where there was some sort of hydraulic issue and the F/E became concerned about a potential Skydrol mist in the area, so we quickly left. I don't know if I would have had the same concern at the time which shoes that it is nice to have a good professional flight engineer with a maintenance background.

[172_driver]

I don't know if I would have had the same concern at the time which shoes that it is nice to have a good professional flight engineer with a maintenance background.

Indeed. In a previous airline it was common practice to leave hydraulics on during turnaround without a thought about the consequences. Then I was accompanying a mech during a turnaround who shared his experience with a wheel well leak. With a tiny hole and 3000 psi the streak of fluid will be thin and hard to detect.

[fantom]

We were shown a video in the RAF when we started the F4 course. A ground engineer put his hand into a wheel well feeling for a leak and 3000 psi severed it.

[dixi188]

"Skydrol® 500B-4 hydraulic fluids are Type IV fluids formulated to exceed the rigid specifications of the aircraft manufacturers. They have been in commercial usage since 1978 and have demonstrated outstanding performance".

I think the 1978 date is a bit late. I have worked with it since 1969 and the BAC 1-11 had it from new in 1963. I also think the B707 and DC-8 used it from new.

Did they mean 1958?

[clark y]

Hurts a bit if you get any in the eyes as well. Used to make a good paint stripper too.

[DaveReidUK]

Hurts a bit if you get any in the eyes as well.

And elsewhere ... :O

[777AV8R]

Leather shoes.......

If you want to see the leather soles of your shoes disappear, step in Skydrol...and the smell! I had just purchased some nice new shiny uniform shoes...first wearing out...I went to do the exterior inspection. We departed and then the smell became overwhelming. The shoes were actually warm. I took them off and voila...a hole eaten in both. I took them in to my Chief Pilot later and asked if they'd consider replacing them for me....Ha Ha. Bad stuff!

[Hydromet]

On day 1 of my apprenticeship, in the safety lectures, we were warned of the dangers of Skydrol, the dangers of getting it on the skin, the mist and the ability of a jet of it under pressure to damage humans.

[deanm]

Further to fantom, my dad was a RAF engines & airframes bloke.

I remember him telling me how, when the Lightning was introduced with its astonishingly-high pressure hydraulic system (to save weight), quite a few techies sustained injuries - including amputated digits.

It seems that the standard way to identify the location of a leak was to run a finger along the hydraulic line. This was fine with the older, low pressure systems, but very not with the Lightning.

Dean

[megan]

ability of a jet of it under pressure to damage humansLikewise gas under pressure. Using the air hose in the workshop to blow debris off your clothing, for example, if mishandled can cause an embolism.

Which raises a question, the British were very fond of pneumatics (brakes, flaps, undercarriage), so why the preference for hydraulics now a days. Besides making tracing leaks rather easier.

[westhawk]

Actually it's electric torque motors which seem to be preferred in new designs now. The latest generation of full-motion simulators and hypersonic research vehicles first, followed by the B-787. Replacing hydraulic pumps, pipes and actuators with bigger generators, more wires and motors seems to be considered superior by designers these days.

Pneumatics are high maintenance and limited by the compressible nature of a gaseous fluid medium. Worked well enough for the Whistle Pig (F-27) I suppose. Not very practical for bigger jobs though.

Hydraulics are highly reliable and can produce very large forces and motions with relative efficiency. But they do tend to weigh more than electric actuation systems. And contamination of the fluid system can cause lots of extra mx hours.

As for Skydrol or Hyjet, ester based fluids are a an extreme irritant to humans. Any exposure to sensitive areas of the body will result in a burning sensation that can't be easily ignored. Note that aircraft mechanics working around Skdrol tend to do much more vigorous hand washing before using the lavatory than after! Breathing misted Skydrol is nearly as torturous as the "gas chamber" in Army basic training. Altogether nasty stuff to work with. Skydrol is more fire resistant than 5606, but is still subject to ignition with a high pressure leak and sufficient heat. It's a matter of degree.

They showed us a video at tech school where a Monsanto employee drank a cup of Skydrol 500A to demonstrate it's non-toxicity. Yeah Id like to see him do that with a cup drained from an actual in-service airplane hydro system!

[Amadis of Gaul]

Leather shoes.......

If you want to see the leather soles of your shoes disappear, step in Skydrol...and the smell! I had just purchased some nice new shiny uniform shoes...first wearing out...I went to do the exterior inspection. We departed and then the smell became overwhelming. The shoes were actually warm. I took them off and voila...a hole eaten in both. I took them in to my Chief Pilot later and asked if they'd consider replacing them for me....Ha Ha. Bad stuff!
Took the black off my less-than-a-week-old shoe about a month ago.

[Uplinker]

I have worn Doctor Martins shoes for many years now.

The soles are resistant to oils and acids, and deice fluid, etc.

Well worth a couple of quid more, especially since they last for years.

.

[Krystal n chips]

" They showed us a video at tech school where a Monsanto employee drank a cup of Skydrol 500A to demonstrate it's non-toxicity. Yeah Id like to see him do that with a cup drained from an actual in-service airplane hydro system

To quote a certain tennis player.." you cannot be serious ! "......not yourself by the way, just the reference to the individual who drank the stuff. :ugh:

Plenty of Skydrol "encounters" and a couple of precautionary trips to A&E over the years....burns quite well actually, watched a leaking hot brake unit ignite one day on stand by way of example.

Always wondered over the years as to why the RAF's hydraulic fluid of choice, OM-15, was never used in the civil aviation world given it's far more benign towards humans and materials.

[westhawk]

To quote a certain tennis player

Good ol' Johnny Mac!

watched a leaking hot brake unit ignite

From a safe distance I presume!

[FE Hoppy]

CSeries has electric brakes but it's hard to see the magic pixies when they leak out of the brake lines!!

[westhawk]

CSeries has electric brakes but it's hard to see the magic pixies when they leak out of the brake lines!!

True, but often the visual manifestation of pixie leakage is smoke. It's all rather easily explained in precise detail in THIS (http://thecompassadjuster.com/education/resources/smoke-theory-of-electricity.html) paper.

[mustafagander]

westhawk,
I love that paper. It always makes me laugh. Thanks for posting it.

[Jet II]

Always wondered over the years as to why the RAF's hydraulic fluid of choice, OM-15, was never used in the civil aviation world given it's far more benign towards humans and materials.

OM-15 is the UK military spec for Mil-H-5606.

[riff_raff]

Both good and bad with Skydrol. Significantly reduced the fire hazard from hydraulic fluid leaks. But Skydrol fluids are also hard on the skin of service technicians, and require special seal materials and any paints/coatings that will come into contact with the fluid.

The current approach with aircraft flight control actuation systems is electro-hydrostatic actuators (EHA's). This is a sealed, self contained hydraulic actuation circuit pressurized by an electric motor driven pump. Much less prone to leakage.

[Private jet]

It certainly will burn under the right conditions. On the only engine fire aftermath I have seen, the skydrol had turned into a dark brown, glutinous treacle like substance.
I also recall the atmosphere in the hydraulic bay on TriStar aircraft was always oppressive with skydrol mist/fumes.

[Wodrick]

One thing to remember that is known by ground staff but not always pilots, Milk is The Thing to counteract Ester based fluids that have got where you don't want them.

[tonytales]

Ah Skydrol! First ran into Skydrol 7000 (green juice) in mid-1950's when it was used in cabin superchargers of DC-6 and DC-7 aircraft. It had better lubricity than mineral fluids. When you opened the bottom hatch aft of the #1 and #4 engines to check the cabin superchargers, you had to be careful not to look up at it as sure as anything, a leaked drop would target your eye. Milk was the best thing to neutralize it. And yes, as a techie you spent a lot of time washing your hands BEFORE relieving oneself than in the sanitizing after. One of our customers, I think it was Alitalia, used 7000 in the aircraft hydraulic system. Notably, no Constellations were converted to Skydrol as they would have been unapproachable with their leakage.

The 707 and DC-8 jets brought us Skydrol 500 (purple shade). Private Jet is right in that the Hydraulic Compartment on the L-1011 Tristars could be uninhabitable. I've seen pinhole spraying leaks that left everything in there saturated and dripping. You literally needed respirators.

Worst I ever experienced though was an Eastern Air Lines DC-9-30 at KEWR that had an internal leak through the system relief valve. The fluid badly overheated and turned into a black revolting gunk. The smell was so bad several mechanics actually upchucked from breathing fumes after opening lines. I nearly did too, it was absolutely stomach churning. We changed just about every component in the left hydraulic system and did lots of flushing of the lines. Overheated brakes could also cook the fluid but the quantity being below the lockout deboosters was nothing like a whole system.

Pin-hole leaks are dangerous in any high pressure system, gaseous or fluid. They may be nearly invisible even in a fluid system. Passing a hand or arm through it and can end with an embolism or fluid under your skin and even severing of digits although I am happy never to have seen that. We were specifically warned of that on the Britannia which had the highest system pressure I ever worked on. It of course used mineral fluid.

With regard to the soles of shoes, one fellow techie bought a new pair of ankle-high work bots with corrugated rubber soles. He worked that first night while changing some hydraulic component in the wheel well and consequently continually stepped in a Skydrol puddle. Next day he pulled them out of his locker. The soles had expanded sideways and in thickness. They looked like the shoes of clowns in the circus or could have doubled as snowshoes.

[Piper19]

Now you know why mechanics wash their hands before going to the toilet. Something may be itching a while otherwise...

Skydrol is very irritating and slippery, but not nearly as unhealthy as engine oils and other greases we use on daily basis.
It can cause serious damage to your body if you are exposed to a stream of 3000PSI, that's the same as a waterjet cutter.
I also ask myself how they dispose of waste hydraulics (it looks like a brown smudge after it's been used).