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 Post subject: Re: My Citation V AOG event
PostPosted: 15 Jan 2023, 14:14 
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Username Protected wrote:
Great write up, thanks for taking the time to do so. I learned a few things about hydraulic systems.

AOG maintenance events are expensive! I will for sure carry tools as a preventative measure!

I'll echo what Jon said. Really a great write up with excellent photos to match. Makes me think about all those aluminum tube fuel lines in my Baron....


Sven,

Since you mentioned your aluminum fuel lines, a friend with a T-310 had his fuel lines replaced with stainless steel. They ran behind the engines, and the concern was for engine fire. I don't know about a Baron, but I'm going to have the engine compartment fuel lines on my 182 looked at.

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 Post subject: Re: My Citation V AOG event
PostPosted: 15 Jan 2023, 14:20 
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Do any of these planes using hydro pressure to operate systems provide any indication of reservoir level other than a low level switch ?

Mine doesn't, all I get is a low level caution if the plunger reaches the microswitch. This is some amount before empty, but if I get there, then I've lost a lot of fluid and I should expect nothing will operate very soon.

During the prior flight, I did not get any abnormal indications at all, and based on the fluid on the ground, most of it leaked out after we parked.

You can see the switch on the plunger here:
Attachment:
hyd-reservoir-1.png

Without hydraulics, I have lost landing gear, flaps, speedbrakes, and thrust reversers.

Landing gear can be put down using the emergency system which releases uplocks and it free falls. A pressure bottle provides more assurance.

If I saw the hydraulic low level come on, I would be tempted to put the landing gear down immediately and fly gear down to a nearby safe landing. By doing this, I don't take the chance the emergency system fails (it depends on cables to release the uplocks, if a cable breaks, you won't be able to get that gear down). I don't need flaps, speedbrakes, or thrust reversers to land safely.

Max gear extending speed is 250 KIAS. Max gear extended speed is 292 KIAS (Vmo). So the gear can be dropped at high speed and stay out at higher speed.

Mike C.

So very important to know your systems. Not knowing, or ignoring, will be at your own peril.
Years back took care of a FG-1D Corsair. A combat vet, It served the last month of WWII in the Pacific.
I noticed some weird scrape lines on the lower MLG legs. 1 was across the head of a clevis bolt. This was mid 90s.
Post war it was based at Glenview NAS in a Reserve Sqd.
Reserve Ensign was flying in 1949.
His wingman called out to him his tailwheel was slowly extending. Pilot checked gear handle and then used cockpit handpump to pump the gear back up.
Later drooped again and then cowl flaps started to open.
Pilot then pulled out of formation and headed back. He finally realized what was happening.
The Corsair Hyd System had the Cowl Flaps and Tailwheel with springs built into the mechanisms. If Hyd Pressure goes away the Tailwheel will extend and the Cowl Flaps will open. Hyd pressure will hold them up and closed, springs will push them down and open.
The Hyd Tank has a stand pipe that rises above the bottom. This feeds the engine driven hyd pump. The bottom of the tank feeds the hand pump. If you have a failure that pumps the main system dry, you can pump the gear down and the flaps with the hand pump as some fluid will remain.
If you don't understand the system and how hyd system failure manifests, then you will be like this Ensign and pump your Emergency Hyd Fluid Supply overboard.
When he selected Gear Down the MLG dropped down, but couldn't be locked due to a lack of fluid. The Gear extends into the airstream so gravity isn't enough to lock the MLG gear down. The tailwheel took care of it's self as mentioned.
There is also a CO2 Blow Down system. Bottle and lever in the cockpit, separate lines to shuttle valves by each gear actuator. This is for use when your hyd system is failed.
Pilot slowed and hit the CO2 and CO2 dispersed in the cockpit. MLG still was dangling and not locked.
Seems they would remove the CO2 bottle monthly and weigh it it ensure it was full. There was a flared alum line and nut connections. The multiple loosen and tighten cycles had thinned the alum material at the flare and had cracked the line. The pressure applied when he fired the bottle broke the connection and vented the contents into the cockpit.
Pilot was forced to land and the MLG folded, the bottom of the MLG struts slid on the asphalt making the marks I noticed 50 years later. Because the MLG legs rotate as they retract this allowed the contact with the asphalt.
This all was explained in a couple of Navy Reports in with the Navy records for #88303. One was a Maint report detailing how a seal failed in a gear door actuator, allowing the fluid to exit overboard, and the damage done as this progrssed to the landing.
The other was a, You Were a Bad Pilot, report by the Operations folks.
Aircraft was repaired onsite and flew again. 1952 it went to the Philly Navy Yard as an instructional airframe. IIRC 1958 it was surplussed and became a civilian.
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 Post subject: Re: My Citation V AOG event
PostPosted: 15 Jan 2023, 14:27 
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Username Protected wrote:
I know electric actuators weren't really an option when these things were designed

Oddly enough, the 500, 501, and 550 models used electric flaps (with two coupled motors). The later S550, 560 models use hydraulic flaps.

There are pluses and minuses to each kind of system. Hydraulics tend to be lighter and more reliable overall, but messier to fix. Electric motors fail more often, require gear trains, and can melt, but can't leak fluid.

The MU2 was all electric except for brakes (which you don't use). I've seen numerous issues with motors, gear trains, relays that have affected those systems.

Mike C.


Mike,

Thanks for sharing your unfortunate experience. Seeing the hyd reservoir down just a little bit and no sign of a leak, I think most of us would have flown also. You did a good job finding MX and getting back in the air.

Skyrol; our Flight Engineers were issued extra uniforms because of their exposure to Skydrol, as they not only did the pre-flight, but had to do field repairs if no maintenance was available. We carried tubing in our spares; landing gear was the main culprit.

Electric flaps; I suppose in a total electrical failure the flaps could be deployed by the battery if still having power, but are there any numbers for a no flap landing, how fast?

Edit: For a jet I'm surprised that the flaps don't have an alternate extension source.

Last edited on 15 Jan 2023, 14:57, edited 1 time in total.

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 Post subject: Re: My Citation V AOG event
PostPosted: 15 Jan 2023, 14:52 
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Username Protected wrote:
Electric flaps; I suppose in a total electrical failure the flaps could be deployed by the battery if still having power, but are there any numbers for a no flap landing, how fast?

For a no flaps approach and landing in the MU2, 150KIAS on the approach, 140KIAS Vref before landing, and then a weight dependent speed (roughly 120-125 Kias) for the final touchdown speed. Here’s most of the no-flap landing checklist.
Attachment:
A853956F-8485-4393-A44B-623416553976.jpeg


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 Post subject: Re: My Citation V AOG event
PostPosted: 15 Jan 2023, 19:48 
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Username Protected wrote:
The Phenom has a page in the G1000 that monitors hydraulic pressure and will CAS message if it drops.

I get the follow caution lights related to the hydraulic system.

HYD PRESS ON - system is running at high pressure
HYD FLOW LOW LH/RH - indicates low hydraulic flow from an engine
HYD LEVEL LOW - indicates low reservoir level

I noticed a flickering HYD FLOW LOW RH last year which allowed me to replace my right hydraulic pump before it failed.

My AOG problem caused no abnormal lights. The majority of the fluid didn't leak out until after the flight. I suspect HYD LEVEL LOW would have been on after the leak.

HYD PRESS ON should not remain on after a hydraulic subsystem has finished its action. If it stays on, the bypass valve has stuck closed (or there is an electrical fault holding it closed). The hydraulic system will overheat in a few minutes in this condition which is very bad since the fluid will turn acidic under those conditions. So you make sure the HYD PRESS ON light goes out.

Mike C.

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 Post subject: Re: My Citation V AOG event
PostPosted: 15 Jan 2023, 20:08 
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Username Protected wrote:
Electric flaps; I suppose in a total electrical failure the flaps could be deployed by the battery if still having power, but are there any numbers for a no flap landing, how fast?

No flap landing is Vref + 15, landing distance +20% per the AFM. It is not a big deal.

Quote:
Edit: For a jet I'm surprised that the flaps don't have an alternate extension source.

No need on a Citation, the big wing makes a no flap landing rather benign.

The MU2 is more affected since it has a small wing and full span flaps. The no flap landing is not difficult, but is quite nose high attitude.

No hydraulics is not particularly dangerous. Gear goes down manually, no flaps, speedbrakes, or TRs. No big deal, just fly a little faster and find a longer runway. The main issue is whether the engine driven pumps will run dry and get damaged. I suspect you get a period of time they will survive, possibly 30 minutes or so.

Mike C.

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 Post subject: Re: My Citation V AOG event
PostPosted: 15 Jan 2023, 20:16 
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Paul, I’m sure Cessna does have numbers for Mikes V. The Mustang does have no flap tables, I’d have to confirm but if I remember correct, you basically add 50% runway length to your calcs. Approach speeds are obviously increased but it’s not going to take a 10k’ runway to land.


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 Post subject: Re: My Citation V AOG event
PostPosted: 15 Jan 2023, 20:45 
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Username Protected wrote:
HYD PRESS ON should not remain on after a hydraulic subsystem has finished its action. If it stays on, the bypass valve has stuck closed (or there is an electrical fault holding it closed). The hydraulic system will overheat in a few minutes in this condition which is very bad since the fluid will turn acidic under those conditions. So you make sure the HYD PRESS ON light goes out.

Interesting. How does this interact with engine driven hyd pumps? Do you have any way to “turn off” the hyd pumps in the event the HYD PRESS ON indicator remains on/stuck?

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 Post subject: Re: My Citation V AOG event
PostPosted: 15 Jan 2023, 21:03 
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Username Protected wrote:
How does this interact with engine driven hyd pumps? Do you have any way to “turn off” the hyd pumps in the event the HYD PRESS ON indicator remains on/stuck?

There is no way to turn off the engine driven hydraulic pump other than shutting down the engine itself.

If HYD PRESS ON stays lit, the procedure is to go through the various subsystems and pull breakers hoping you can drop the system holding the bypass valve open. If you find the offending system, leave that breaker pulled and deal with not having it.

If pulling breakers doesn't fix the HYD PRESS ON, then the valve is stuck or there is some other fault which is keeping the bypass valve closed. The checklist says to land as soon as possible in this case.

Mike C.

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 Post subject: Re: My Citation V AOG event
PostPosted: 15 Jan 2023, 23:28 
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BTW, is there an STC to change to 5606 on the older Citations? My aircraft came originally with Skydrol, but got converted to 5606 sometime in the 80's.

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 Post subject: Re: My Citation V AOG event
PostPosted: 15 Jan 2023, 23:43 
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Good write-up. Ive been working on a 560 Ultra all week and I think I'm calling Jet East next time anyone goes into that aft equipment area. :dancing:

Alcohol is the best cleaner for Skydrol inside the aircraft to be sure. At my last flight department (Gulfstream Operation), we bought every degreaser on the market to try in the hangar and for general cleaning. There was one clear winner when it came to Skydrol clean-up on the outside of the aircraft... gear, tires and belly... Spray Nine! For some reason it was King and would neutralize the Skydrol and remove it effectively.

We bought a 12,000hr 560 a few years back that had worked hard for a mining company in Canada and Alaska. They had built up spares of 3,000psi steel-braided flexible lines in various lengths and sizes with Fittings common to the 560 for their fly-away kit. They used them to get back to base in an event such as yours. Necessity is the Mother of Invention.

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 Post subject: Re: My Citation V AOG event
PostPosted: 16 Jan 2023, 00:25 
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BTW, is there an STC to change to 5606 on the older Citations?

Not that I am aware of.

I suspect the parts expecting phosphate ester won't work well with mineral oil (base of 5606).

Quote:
My aircraft came originally with Skydrol, but got converted to 5606 sometime in the 80's.

Maybe such a kit included a bunch of seals to replace?

Mike C.

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 Post subject: Re: My Citation V AOG event
PostPosted: 16 Jan 2023, 00:27 
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Username Protected wrote:
We bought a 12,000hr 560 a few years back that had worked hard for a mining company in Canada and Alaska. They had built up spares of 3,000psi steel-braided flexible lines in various lengths and sizes with Fittings common to the 560 for their fly-away kit. They used them to get back to base in an event such as yours.

Fixing the line is only half the problem, you need a means to get the fluid back into the system, some sort of pump.

Mike C.

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 Post subject: Re: My Citation V AOG event
PostPosted: 16 Jan 2023, 10:18 
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They make a small canister that looks like a garden sprayer that you pump up by hand that’s worked well to refill Skydrol .


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 Post subject: Re: My Citation V AOG event
PostPosted: 17 Jan 2023, 19:02 
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I had a leak in an aluminum hydraulic line on the conquest a couple years ago. Incredibly, Cessna had one on the shelf for $94 + $112 for overnight freight. It came primed and ready to go with fittings. Even your line at +/- $1k including freight, it can be hard to justify trying to make one especially AOG with a gun to your head in terms of time. If you don't use that flaring tool on a regular basis it can take a few tries to get it right. It's great they had one on the shelf.

What is the advantage of skydrol vs 5606? It seems like skydrol has all sorts of disadvantages but there must be a reason they used it at some point.

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