Q for pilots

[Mitch Cronin]

Hypothetical question:

Imagine you're in a 67 and your left EDP (primary hydraulic pump) craps out on you... you're running the left system on the ACMP now... and losing left side hydraulic juice... you know that sooner or later that left side ACMP will cook itself too... all is just peachy with the center and right systems... How long do you run that left side ACMP? What are the SOP's to handle that?, and if there's judgment involved, at what point do you hit the off switch for that AC Pump? After it stops putting out useful pressure (at which point that pump is going to be cooked too)?, or sometime before that, hoping to save the company the expense of an additional pump?

The reason I ask is because the question came up at work last night... there were a few people suggesting the extreme low quantity fluid status should cue the pilots to save the pump.... I figured the thoughts would be more like: "I'd like to get this airplane home safely and I can do so much more assuredly with all three systems working for as long as they can" with nary a thought for pooching another pump.

Whaddya got for me?

[Guest long keel]

Mitch,

Usually the SOP deals with situations like this. I don't know the 767 SOP's, but here is the usual process on the A320 for most abnormal situations.

1) ECAM, (on screen checklists)

2) QRH, (Quick reference handbook, ie paper checklist.)

Now if control of the airplane is not an issue, it is time to get out the MEL, go through dispatch to get a link to maintence control and get a plan that satisfies the Captain, and hopefully addresses the needs of the other parties. This is when considerations such as saving the pump or engine, time to field, overweight landings, wx conditions at arrival airport, field length (if there is a possible brake failure and a heavy airplane), all start to get thrown in the mix to come up with the best overall solution.

I know this doesn't answer why the crew did what they did, but at least it explains the process that lead to their decision. I hope this helps.

Cheers,

lk

[Dork]

Just off the top of my head.....

Don't have a QRH handy, but the first thing I look for when you are talking about HYD pump loss is the fluid. If it is squirting out shutting down the pumps is called for in most check lists. The trick is to note the fluid loss early on and get the "right" checklist, while being "distracted" by the pump failure.

The "saving" of the second pump may end up being a good side benefit. Don't know if that answers you question..maybe someone has a QRH handy.

[J.O.]

Mitch:

While I don't know the specifics of the 767 system, I would definitely consider shutting down the ACMP in the hope of stopping the fluid loss. By keeping some fluid quantity, the system could be restarted just prior to landing to assist with landing gear extension, brakes and flight controls during the most critical stage of the flight.

Jeff

[Trader]

I think most pilots would run the system provided that there was an operational benefit or necessity. If it was not required and safety wasn't affected then I would shut it down to save the fluid for possible use later (as Jeff wrote) and aviod having a system operating that was not functioning properly.

I don't think I would want to "cook" a pump and deal with any additional problems that it might creat- ie. fire

[Guest Starman]

Hey Mitch,

The QRH says that if it's a Demand pump pressure problem, first turn the pump to "ON" instead of "Auto" and if the pump output continues to be a problem, turn the pump "off". You can run on the electric primary pump after that, but if the problem is a system pressure problem, usually caused by low quantity, turn that pump off as well, which makes sense, because running the pump without fluid will cause overheating anyway and might even present a fire hazard.

The QRH doesn't really care about quantity until the low quantity causes low system pressure, but from experience, if there is a leak in a 3000 psi hydraulic line, it usually depletes itself pretty fast anyway, and you'll be getting pump pressure lights as well as system low pressure messages.

In the case of the left system, it's no big deal anyway. You just can't use the left autopilot (so no Cat 3 landings), and the aircraft is fully controllable until a full stop is made at an appropriate airport.

Bottom line is, there's no point running a pump if you aren't pumping anything, and when it comes to hydraulic systems on the 767, two out of three ain't bad...

Kinda reminds me of a flight many moons ago, when I was an F/O on the 737, coming back from Mexico on a late night charter with a particularly favourite Captain. Those flights were always a bit of a "mission" on the 37, trying to squeeze every last mile out of the fuel available. We were within a pound of minimum fuel at each waypoint and up near Bismark when I noticed that the hydraulic quantity was dropping. When I pointed this out to the Captain, he leaned over to study the gauge for a minute and then said, "Good. We're reducing the zero fuel weight. We'll make it now...)

[Mitch Cronin]

Thanks for the responses Gents... Upon further reflection, it does seem rather evident that there could be many different scenarios... fluid loss rate could range from really s-l-o-w to all-gone-right-now... With the demand pump initially in "auto" and fluid loss being quite rapid, it's not hard to imagine that second pump being run a wee bit too long to save it, even just in the time it takes to look in the QRH.

Starman... It's always nice to be with folks who can take a little setback with that kind of obviously unshakeable calm.

...in the 37, with A leading to B leading to Standby ...leading to cables flying ballanced flight controls.... you could almost say: we don't need no steeenking hydraulics

Cheers all,

Mitch

[Guest Starman]

I don't know if you've ever flown the 37 sim in manual reversion, but it's kind of like driving an old pickup truck with a lot of slop in the steering box.

I've flown the aircraft that way and it wasn't bad at all at altitude. However, I know a guy who landed one in Dorval years ago in manual reversion for real and he said it was a lot easier to land the aircraft than the sim.

On the way back from Mexico the hydraulics stopped pissing out just before the 1.8 gallon standpipe, but the 37 was great that way; you just didn't have to worry too much.

Here's a Q for you. When you replenish the hydraulic fluid, do you fill the systems at different times and/or with fluid from different sources? Whenever there is a problem with a system, I always suspect contamination (ever since I ruined a brake system on a truck that way ). If a system seal blows, it makes me suspicious of the other systems and whether all the systems might be contaminated.

The 37 was no big problem with no fluid, but larger aircraft sure are...

[Guest gldd]

On the 707's and 727's, Boeing calls for pumps off to trap some of the fluid and possibly restart to operate one of the required items such as flaps or gear. Hope this helps. At least this was the procedure many years ago.

[Mitch Cronin]

"I don't know if you've ever flown the 37 sim in manual reversion, " Never tried it... wish I had, now.

"but it's kind of like driving an old pickup truck with a lot of slop in the steering box." I have tried that!

When we fill hydraulics, most often it's a top up to any or all systems from the same source(s)... (usually freshly opened cans) I think one of the greatest risks of contamination would come during use of a hydraulic ground cart used for systems testing... Often, when the pressure is removed, all the fluid is dumped into the reservoir in the cart, then pumped back to the aircraft... the carts have filters of course, but it's not us that maintain the carts. That would most often only involve a single system at a time though.

The worst cases of "contamination" I've ever seen have been self induced... that is, something in the aircraft has self destructed and turned the fluid into something resembling metallic flake paint. In the case of a PTU that can mean two systems are affected.

I've heard of, but never witnessed the results of, others having contamination from wrong fluids being added. I think that'd be pretty hard to do, since skydrol is such a unique sort of juice.... ....then again, I've seen sleepy people do some odd things... like put the coffee pot in the fridge.

We once had an aircraft type that seemed to have problems with excess water absorption in the hydraulic systems... (if memory serves, there was also an issue of some kind of chemical changes happening in the fluid) so we regularly sampled the fluid (every A check - all 3 systems) and sent the samples off for analysis... and changed the fluid fairly often... Haven't seen that happen in a long time. I think that was an earlier spec fluid and we've long since moved to a different spec. for Skydrol.

[Guest Starman]

Thanks for the info, Mitch.

I guess that most pilots tend to look through the stats on multiple system redundancy and be a bit suspicious when something strange happens to one system. For example, if an engine quits with good reason, the chances of the second one (or third or fourth as the case may be) quitting is statistically next to impossible (mind you the chance of the remaining engine having a problem running at MCT may be slightly higher, but still miniscule), however, if an engine quits for a reason that may be related to fuel contamination, your faith in the remaining engine is reduced dramatically.

A good example was the L1011 down south that took off with no "O" ring seals in the oil filler caps and had to return with some drama a number of years ago. If a human mistake is repeated over multiple systems, the system redundancy doesn't mean much.

In the same way, it may be no big deal to fly over to Beijing with one hydraulic system out, but if you're over Alaska, staring out over Siberia, and a system quits, you might think it prudent to drop into a friendly airport rather than take the risk that the remaining hydraulic systems may fail for the same reason.

However, in my time on the 767 ETOPS fleet, the maintenance reliability of primary systems has been outstanding. Usually the most stressful decision we have to make is where to go for "Gyoza".

[conehead]

Hey Mitch; the airplane in question is now u/s in Manchester. Snag is "L HYD PRIM PUMP OVERHEAT. TURNED OFF".

I thought you fixed that???

[Homerun]

Mitch, a few years ago I had that almost identical problem, minus the fluid loss. Left EDP packs it in, after being changed on the ground, electric pump takes over. We were heading overseas and this happened over YUL. We had a lengthy discussion as to whether we could enter the ETOPS area in this condition. QRH says all 3 systems pressurized and operating normal. Capt tells me that the pump isn't part of the system and we can go. I say no way. MOC says up to the Capt. A quite heated discussion ensued and I got overruled. Talked to a manager after and he says going was the right decision. I still disagree. What do you think?

[Mitch Cronin]

Conehead: "The airplane in question" was supposed to be "hypothetical".

But no... All we could do was replace some of the components... parts nil stock meant the fix (flushing, bleeding of the system, and determination of the fix) went to the day shift.

Sounds like we have a bigger problem though... What's cooking those pumps??

Homerun... short answer: I agree with you.

....Longer answer: I'd say if the MEL says you can go ETOPS without the EDP, and no physical checks are required first, you're good to go... but I'd be very surprised if it said so... I sure have trouble with the notion that "the pump isn't part of the system".... "operating normally" would mean the primary pump is doing it's thing, not that the "demand pump" is now your primary pump. .....and even if the MEL allowed for it, if I were in the bird I'd sure feel a whloe lot better if someone were able to confirm first that the system was clean (filters checked at least) ... and again, IF the MEL allows for ETOPS dispatch in that condition, I'll wager it calls for some checks first.

I don't like accepting lost redundancy when you're not dealing with getting the bush plane back to base.

[Homerun]

Thanks Mitch. The MEL does not allow for dispatch period when the EDP is inop let alone ETOPS.

Cheers

[Mitch Cronin]

Right you are Homerun... I checked that myself last night... (I'm not a frequent user of the MEL... working in the hangar we generally try to fix rather than lean on that book.... so I frequently don't know what's there until I look... I'm often surprised to find relief under the MEL that I thought shouldn't be there)

So, knowing that... even though the MEL isn't the deciding factor once you're already airborne, ... I'd say you were definitely right. The argument that the pump isn't part of the system is nonsense.

I also checked on "the airplane in question"'s status... and discovered Conehead was pulling my chain! Conehead... you dog!!! ....no left EDP failure at all.... (man!.... some people's kids! )

[Mike Lavoy]

I also checked on "the airplane in question"'s status... and discovered Conehead was pulling my chain! Conehead... you dog!!! ....no left EDP failure at all.... (man!.... some people's kids! )

Thanks for the laugh conehead. Isn't it fun watchin' him get all wound up?

[conehead]

Thanks for the laugh conehead. Isn't it fun watchin' him get all wound up?

Yup! You guys won't see me next week. I've served my sentence, and will return to the Ramp next week. Been a pleasure though; nice guys on that crew!

[Guest rattler]

Some interesting information re "Skydrol". I can remember in the 70s asking about the chemical makeup of Skydrol and it's possible negative effects on those exposed to it, if only we had this information available then.

Skydrol Facts