A short history about Skydrol
 

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

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.

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.

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.

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.

"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?

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

And elsewhere ... :O

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!

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.

RAF Lightning
 

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

Likewise 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.

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!

Took the black off my less-than-a-week-old shoe about a month ago.

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.

.

" 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.

Good ol' Johnny Mac!

From a safe distance I presume!

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 paper.

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