Boeing 777 HYD QTY LOW C .

[Herbie65]

I recently encountered a HYDR C leak, after 3 hours of flight we were confronted with the EICAS msg HYD QTY LOW C and the msg RESERVE BRAKES/STRG. The system indicated a qty of 0.39. within 30 minutes it was down to 0.30.
So we diagnosed this as a real leak and not an indication problem.
We calculated that the system would be empty within 1,5 hours. The remaining flight time was more than 3 hours. So we would be soon without the hydr c system.
We decided to switch off all hydr pumps from the center hydr system, hopefully to stop the leakage. After switching off all the pumps the leak stopped indeed.
We did this to preserve the oil for the Center system for the approach and landing, so we could use normal gear and flap extension, Have full available spoilers, flight controls, brakes, and nose wheel steering.
This worked, we landed with an hydr qty of 0.06 and the NWS even worked, so we could taxi to the gate.
After talking to our tech pilot and ask him why this isn't a standard procedure, he told me that Boeing said the following about this:

Boeing procedures do not endorse preemptive shutdown of hydraulic systems due to low quantity indications. In the event a hydraulic system continues to lose fluid, the appropriate hydraulic pressure message will annunciate the condition. Boeing procedures for low hydraulic quantity do not shutdown the associated hydraulic system for the following reasons:
Since the leak rate is not known, the flight crew may be shutting down a system which may have continued to work for the remainder of the flight. The flight crew will also need to remember to turn the system back on.
Roll rate and speed brake effectiveness may be reduced when a hydraulic system is shut down.
False quantity indications have lead to unnecessary shutdowns and diversions which increase risks to crew and passengers.
There have been cases where cold temperature shrinkage of hydraulic quantity has led crews to shut down an operative system.

Thoughts?

[CCA]

I'd guess legally Boeing can't say use common sense, so to avoid any legal issues it's lowest common denominator cut and dry. They could never leave it open to interpretation.

[Goldenrivett]

False quantity indications have lead to unnecessary shutdowns and diversions which increase risks to crew and passengers.

Until Boeing fit an independent "Low Level Sensor" then all your information is coming from a single source i.e. a float type indicator (e.g. which may be sinking).
I admire your intelligent diagnosis - but think what would have happened (in the tea and biscuits interview) if it was simply an indicator problem.

[FullWings]

I admire your intelligent diagnosis

Likewise. Losing the centre hydraulic system is not a “land at nearest suitable” event but you do have to think about the repercussions, e.g. a possible gear down diversion.

In this particular case, if faced with a choice of reduced roll rate and spoiler effectiveness in the cruise or in the landing phase, I think I’d want to have more responsiveness at the end of the flight near the ground, especially if conditions were less than benign. I suppose what Boeing are saying is that if it is an indication issue, then you’ve been one system down during the flight for no physical reason so increasing risk. They can’t write the QRH for all possibilities; indeed it has to work for a below average crew who are having a bad day.

Boeing’s view on “troubleshooting” is that you should exhaust all SOPs first and only if the end result is unacceptable should you start making up your own procedures. I have to say I agree with that philosophy but there are edge cases where the application of sensible airmanship can lead to a better outcome. I can’t find much fault with the logic used above but I can see the point of view of management as they don’t want to encourage off-piste operations too much. It’s a fine line and I expect that privately the operator and/or manufacturer might agree with the actions taken but they can’t be seen endorsing something that could easily be done wrongly.

[HPSOV L]

You are not the first crew (or Maintenance dept) to implement this idea. Still, Boeing built the thing and they have been in the business longer than you or I. Best to reign in the urge to be creative unless, as they say, there remains an “unacceptable situation”. Inferring a threat to safety. In principle while you may have been correct, it’s Rummy’s famous unknown unknowns that can bite you when you go beyond what superficially appears to be a lowest common denominator checklist.

[hunterboy]

Why stick your neck out and operate outside of Boeing's recommendations and company SOP's? If it was a life threatening situation, it would be understandable, but a relatively benign HYD QTY LOW? Sadly, I'm not sure the industrial tribunal or court system would take your side had it turned out badly. Follow the SOP's , divert if necessary and go home. Let the company clear up the subsequent mess.
There doesn't seem to be much room left for intiative in commercial airline flying nowadays. When you see the calibre of person running the airlines management, you understand why.

[wiedehopf]

Maybe they also want to avoid the possibility of "managing" the fluid level in the hopes of landing with all hydraulics.

If the quantity is almost zero when you land you could have a HYD C failure on short final.
This in turn means you either need to go around or land without having applied the checklists for landing with HYD C inoperative.

Basically Boeing probably prefer a failed hydraulic system over an unreliable one.

[tdracer]

Basically Boeing probably prefer a failed hydraulic system over an unreliable one.

BINGO!!!
The checklists and procedures are written for a failed system, not one that you don't know what it's going to do and when.

[Cropduster]

Having flown Airbus for most of my career, and recently transitioned to the 777, I find the Boeing mentality is much more a "you don't need to know that," or "don't worry about it." Right to the point it turns out that they don't even want you to know the existence of systems in the aircraft. I was chastised for bringing the ENG page up on the EICAS in cruise. Was told that if Boeing wanted us to look at it, they would have done so themselves. But then over the years we have had 3 aircraft divert to sub-optimal places due to oil leaks that could have been detected in a much more timely way had the crews done this. I understand what the posters above are saying but at the end of the day, we are paid to think and I like both the situational awareness and the thought that went in to your decision.

[tdracer]

Cropduster, it's not that they don't want you to "know about it", it's that they don't want you troubleshooting with a planeload of passengers in the back. That's been known to end very, very badly.
Two examples:
https://en.wikipedia.org/wiki/Alaska...nes_Flight_261
https://en.wikipedia.org/wiki/Easter...nes_Flight_401

There are also suspicions that troubleshooting a problem played a part in the recent Lion Air crash (now that the CVR has been found we should know more before long).
BTW, since engine oil quantity is displayed on primary EICAS, what could you have learned about an oil leak by checking the ENG page?

[HPSOV L]

[QUOTE=

Basically Boeing probably prefer a failed hydraulic system over an unreliable one.[/QUOTE]

I was going to suggest that as well. But when you think about it, in either case (pumps on or pumps off) the point of failure would be unpredictable and is affected by variables such as the length of flight. Just saying...but still agree stick to the checklist.

I once thought it would be a good idea to cycle the Bleed Air switch when I got a Bleed Off Eng message, after all it worked on my old school jet. Turns out, nope, not a good idea at all...

Regarding monitoring oil quantity: Boeing have released bulletins in the past on the subject of oil "gulping" or hiding. Plenty of info if you google it.

[Cropduster]

tdracer....

Are the EICAS pages airline customizable? In normal cruise the only engine parameters that ours display are N1 and EGT. To see the engine oil quantity we have to either select the ENG page on the lower EICAS or "trick" the system into displaying it on the upper EICAS. This is what I was chastised for.

I get what you are saying about trouble shooting but I don't think that noticing a slow engine oil or hydraulic leak in a more timely manner, and thus allowing a more commercially suitable diversion is anywhere near ad hoc troubleshooting. In fact, if you can get it on the ground before you have to shut it down it is far safer and also preserves the fleets ETOPS reliability. If the quantities are not displayed, some really sophisticated software could monitor the rate of change. But why not just display the quantities of what could leak out in flight. The screens certainly have the room. But I object to the philosophy of flying along fat dumb and happy until a message appears saying "O'h by the way, you are almost out of oil and may have to take everyone for an unscheduled stop in outer Mongolia!"

I guess it is just what you are used to. For the last dozen or so years I got used to seeing this information and subconsciously incorporating it into a cockpit scan.

Cheers cropduster

[ScepticalOptomist]

Airmanship

Pulling up systems pages etc in cruise is just good airmanship.

So many seem to have forgotten this basic premise of flight.

Everything you MUST do is in the manual - everything else is airmanship.

[hans brinker]

Originally Posted by wiedehopf

Maybe they also want to avoid the possibility of "managing" the fluid level in the hopes of landing with all hydraulics.

If the quantity is almost zero when you land you could have a HYD C failure on short final.
This in turn means you either need to go around or land without having applied the checklists for landing with HYD C inoperative.

Basically Boeing probably prefer a failed hydraulic system over an unreliable one.

I can definitely see the merit in that. For the manufacturer it is almost always better to plan for the least amount of in the air trouble shooting and go for the standard procedure, so low level, unknown leak, high temperature any other thing seems wrong, just use the checklist to switch it off and the procedure will tell you what is/isn't going to work, without any last minute surprises.
Sometimes that won't work, on some of the A319 (now "fixed" with an OEB) with a green or yellow pump overheat, the procedure was to switch the pump off, and have the system pressurized via the PTU of the opposite side system. Sometimes the overheat would be due to low quantity, and this would lead to the PTU running continuously, and overheating the engine pump on the opposite side. You would then have to switch that pump off too, and would end up with dual failure. Now we have to check if the overheat is due to low quantity, and if so, switch off the affected engine pump and the PTU.
If there was any system that would reduce the risk during the landing phase (not just for A319, but in general like anti-skid, nosewheel steering, diferential braking aso) that I could get back by switching the system back on while on the approach, I would definitely plan for it not to work, but I could see myself switching it back on.

[tdracer]

Originally Posted by Cropduster

tdracer....
Are the EICAS pages airline customizable? In normal cruise the only engine parameters that ours display are N1 and EGT. To see the engine oil quantity we have to either select the ENG page on the lower EICAS or "trick" the system into displaying it on the upper EICAS. This is what I was chastised for.
Cheers cropduster

EICAS does have some customization options - on the original (767/757) there were some 'pin selects' - on the newer stuff there is an electronic file that can be uploaded to customize the display, but it's really limited in what it can change - e.g. units (most of what's displayed on EICAS is governed by the regulations and can't be changed). None of the options I'm aware of affect the oil quantity display (except perhaps units).
I guess I don't understand why you'd routinely fly round without lower EICAS displayed - is that something your operator dictates? From the designer point of view, the "upper only" compacted display is there to cover failures, not something you'd routinely use. I frankly can't understand why displaying and checking the full 'normal' upper and lower EICAS display would be discouraged. Originally, the EICAS displays were CRTs, and the CRTs would wear out, so some operators discouraged routinely using both EICAS screens to preserve CRT life. But the 777 has always used LCD displays that last almost forever - there is no reason not to use both displays.

[Vorsicht]

I would have thought the crew would have been given a fairly firm gentle reminder that in future, follow the SOP's. It is a completely flawed argument to say that the outcome was good, therefore the process is justified. No 777 crew can reasonably claim they have enough knowledge of any system to justify second guessing the EICAS or QRH. Aircraft technical simply isn't taught to that level anymore. The whole premise behind how we operate these days is based on the amount of F*&k ups that have resulted from crews miss diagnosing problems. The assumption behind the Boeing QRH is that they want to take the least risk approach. The least risk approach (in Boeing view) is the operate the aircraft normally until it tells you to do otherwise. Once you have been advised of a system fault, then carry out the QRH actions, it's that simple. Assuming the author is from the Australian operator of 777's, their actions were counter to what is taught and required of crews. Happy to argue all day long as to the merits of those particular SOP's, but the fact remains the crews actions contravened SOPS's. At it's worst, that is a willful contravention of SOP's. Generally not looked upon well these days.

[heavy_landing]

Agreed, just follow the ECL.
Additionally, what’s the point of bringing up the secondary engine instruments to monitor the oil quantity? There’s no checklist that I’m aware of purely because of a low oil quantity indication.
These Boeing guys are clever. Simple, single failures are well served by just following the ECL.

[HPSOV L]

Perfect summary Vorsicht. That post should be cut and pasted onto the front of the QRH.

[hans brinker]

Originally Posted by Vorsicht

I would have thought the crew would have been given a fairly firm gentle reminder that in future, follow the SOP's. It is a completely flawed argument to say that the outcome was good, therefore the process is justified. No 777 crew can reasonably claim they have enough knowledge of any system to justify second guessing the EICAS or QRH. Aircraft technical simply isn't taught to that level anymore. The whole premise behind how we operate these days is based on the amount of F*&k ups that have resulted from crews miss diagnosing problems. The assumption behind the Boeing QRH is that they want to take the least risk approach. The least risk approach (in Boeing view) is the operate the aircraft normally until it tells you to do otherwise. Once you have been advised of a system fault, then carry out the QRH actions, it's that simple. Assuming the author is from the Australian operator of 777's, their actions were counter to what is taught and required of crews. Happy to argue all day long as to the merits of those particular SOP's, but the fact remains the crews actions contravened SOPS's. At it's worst, that is a willful contravention of SOP's. Generally not looked upon well these days.

And sometimes SOP/QRH aren't enough, so I do think there is still room to at least think about what you are doing. In the 777 case I would definitely have coordinated with MX before deciding not to follow SOP. I have had erratic engine indications due to failure if the TAT input to the FADEC on the A320. No ECAM/QRH/SOP available, but after talking with MX we were able to continue by switching to rated mode. If you think you can ALWAYS save the situation by following SOP, we might as well leave the pilots home.

https://avherald.com/h?article=47d74074

[agg_karan]

The Centre hydraulic isolation system designed in 777 sort of isolates the leak in the lines with help of 2 isolation valves (for proper nomenclature refer AMM HYD chap - CHIS)
unless the leak is below the standpipe levels I think CHIS is quite useful.
I think it would be wiser to stick to the ECL and let the underlying design feature takeover and sort the issue.
you might have managed to extract more from the a/c with such a leak than what it intended by switching off CTR HYD pumps and saving your fluid.
While many things are undisclosed in 777 I would always suggest to be fully aware of your smarter options but exercise them wisely espcially when it's out of the book only when there are very compelling reasons.