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Guest airmann

Fuel Logic is it correct??!!!

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Hello, let me begin by stating that I believe that the PSS777-200LR, (I have not tested the 300ER or 200LRF) is not correctly programed in the fuel usage department. I have noticed that other users have had the same problem.Scenario 1: I decided to try out the long range capabilities of the 200LR by flying Mumbai(Bombay)-Vancouver. I set her up, MAX fuel onboard, started FSpassengers and was on my way to Vancouver, Eastbound. I was not going to sit in front of my computer for 17 hours so I made sure that I left the CROSSFEEDS ON. APU was OFFI went to bed, woke up the next morning to check on the progress and found that there was a FUEL IMBALANCE message on the EICAS??? Crossfeeds were on, but for some reason the left fuel tank had used up around 50T more fuel than the right. The center tank had also been emptied, and now had 0.4T left.FIRST PROBLEM: In a Real 777 if the crossfeeds are left on will fuel from the left tank be used up faster than fuel from the right tank?? NOTE thant the APU is OFF. Strange??This is not the end of the problems!!!!SECOND PROBLEM: So i had a fuel imbalance approx 20T in the left and 70T in the right, how it got to be this way I do not know, I decided to switch Crossfeeds OFF. I went about my daily business as there was stil around 7 hours left on the flight, I checked in once every hour or so and noticed that the left tank was still draining faster than the right??? I checked back later and there was around 0.4T in the left tank, realising that I would have to use the right tank to give the left engine fuel I switched Crossfeeds ON and went to go watch TV. Approx 10 minutes later I heard the sound of alarms comming from the my computer, not only to find that the left tank had been drained of all her juice, but BOTH engines were no longer running, autopilot had disconected and I was now performing a deadstick landing into a rural airfield in Western British Columbia. WHY HAD THE ENGINES STOPPED RUNNING??, i had 60T left in the right Tank and crossfeeds were ON, not only had the left engine stopped running, but so had the right!!!!! I tried to start up the engines, but no luck. The EICAS weas showing me 60T of fuel in the Right tank but the engines didn't seem to notice them!!!!!, nor did the APU system which refused to start even with crossfeed on!!!! OK, so that was a huge anti-climax, I was only 1 hour away from vancouver. but nevertheless I wanted to investigate further. I setup this config, SETUP1:0.8 in the Left, 0 in Center tank, and 45T in the Right tank. Sitting at the Tarmac. APU ON, BLEED AIR ON, CROSSFEEDS OFF. Started up Left engine using Left fuel tank, then proceeded to switch APU off, Left fuel pumps off and Crossfeeds off, there is now no Green lines going into the Left engine but it is still running, thats fine, apparently on the ground gravity is enough to allow fuel flow into the engines, the pumps do not need to be on. Started up the right engine now no problem, switched the APU off and switched Right Fuel Pumps ON, crossfeeds were off Left Pumps were off both engines running fine. Eventually the left fuel tank ran out of fuel, BUT for some reason, I lost both Engines????? Why, when the Right Fuel tank has 45T available and Right Pumps ON would the right engine turn off when the left fuel tank runs out of fuel???? Shouldn't the right engine stay on??? All generators, PACK, hydralics and Bleeds were in position for flight.So I connected up External power and gave the electrics some juice, I now wanted to start up the APU so that I could get some Bleed air going to start the Right engine up again, it had 45T available for use. I now had 0 fuel in the left tanks, so I had to open crossfeeds to feed fuel to the APU from the right tanks. I checked the FUEL EICAS and there were GREEN lines showing that fuel was running from the right tanks through the crossfeeds into the APU, I believe this to mean that the APU has fuel running to it and is available for use. But no luck, the APU would not start, for some reason, whatever it is, THE RIGHT FUEL TANKS ARE NOT BEING ACKNOWLEDGED, Flight Sim does not seem to accpet that there is fuel in the Right tanks. So I setup another test to verify this theory. The setup is identical to Setup 1:0.8T Right 0 Center 45T Left.There is Fuel in the Left tank so the APU starts. This time instead of start the Left engine first, I start the right engine ONLY, it starts up OK. APU OFF, EXTERNAL POWER DISCONNECTED, CROSSFEEDS CLOSED. Ok the right engine is running, the APU is off but the Left fuel tank is still being drained, it reaches 0 and with 44.5T in the Right, the right engine shuts down!!!!!!OK PSS or anyone, is there a solution?? why does the right engine stops working when the left tank runs out of fuel and why does the right engine keep sucking fuel out the left fuel tank with CROSSFEEDS OFF!!! Is this how the 777 was designed???Thanks, SheahanP.S. I have tested this with and without FSPassengers, same result each time.

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I don't have this problem.You should always fly with the crossfeeds OFF, unless you need to pump fuel across ship for any reason.Make sure you start the 777 from the defualt FS Flight, I always have, and taken the 777 over many many many miles including Hong Kong to Heathrow the wrong way round, and NOT had a problem.Cheers

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I tried that but it did not work, The right Engine still requires fuel from the left tank to run?? Wow, quite a conundrum!!

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I haven't had this problem either. Maybe, try not flying Mumbai to Vancouver whilst not being on the flight deck so you can monitor the crossfeeds and use them when needed :-roll

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Ian et alAs you, I have flown several 12+ hr routes with the LR with no fuel problems. But I have never had the fuel on one side run down to zero.I've now looked at this in more detail and I agree with Sheahan - if the tanks on one side reduce to zero, the PSS 777 assumes no fuel anywhere. Scenarios:1. Cruising at 30,000 ft, fuel in one side reduces to zero, both engines flame out whatever the fuel contents on the other side or the crossfeed #### settings. In detail - when the "low" side reaches 300 lbs, the pumps on the "high" side also shut off, pres lights on, and shortly after low side contents reach zero both engines flame out. 2 On the ground, engines off, fuel on one side, zero on the other side - neither engine can be started. Applies to either side although if the fuel is on the left, the APU can be started but not the engines.As to crossfeed, as far as I can see, opening the crossfeed and shutting down the pumps on the low fuel side allows the high fuel side to provide SOME fuel to the other engine - the low fuel side continues to reduce but at a lower rate than normal. This allows fuel balancing but you can NEVER move fuel from the high side tanks into the low side tanks - you can only reduce the rate at which you are using fuel from the low side. Eg, in the cruise, the high side reduces at twice the rate of the low side.So far, I cannot see anything that we are doing wrong but we may have missed something in our switchery? Of course, allowing tanks to get so low in the first place is v poor airmanship and we all know of earlier aircraft where you could lose all engines with plenty of fuel trapped in the system. But nowadays designers usually take into account Murphy's Law - and I suspect that the rw 777 fuel system does not suffer from such peculiarities?Only my installation, of course, but I'll look at Sheahan's other points and try it on another system tonight to make sure.Regards to allJohn Rooum

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Now had a look on a second system with the same result:1. In normal operations the fuel system is fine - any small out of balance can be easily rectified using the cross feed.2. The anomalies were as before: a. If fuel pressure on one side falls with zero fuel on that side, both engines shut down b. Left and right tank systems cannot be isolated. c. Crossfeed only moves fuel into the opposite engine feed; even with pumps on the low side to off, no fuel can be pumped into the low side tanks.John Rooum

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Question: Differences with rw plane aside, how is it possible with the PSS T7 to set up a test with fuel on one side? The fuel setup panel accepts a single figure, nothing more.Is it like the 744, where the fs9 fuelling menu causes issues?edit - guess not - manual just says setup panel is for 'optimal loading of fuel' - nothing about not using fs9 menu.regards,Markhttp://www.precisionmanuals.com/images/forum/747400.jpgXPHomeSP2/FS9.1/3.2HT/1024mb/X700pro256

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I have also seen that when the APU is running it is impossible to switch the left forward pump off. So I think this pump is necessary to feed the APU.Guy

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MarkI also looked at it just using the PSS set-up. That threw up something else which I did not mention above. Try this:1. Load the 777 at the gate2. Set the fuel using the PSS set-up. Any level but try something like 2000 lbs - its more interesting.3. Start the APU - more lh fuel useage.4. Shut down the rh engine, shut off the rh fuel cocks and ensure crossfeed closed.5. Watch the fuel useage - on my system rh engine fuel flow shows zero but the rh tank contents reduce at the same rate as the lh tank contents? Both tanks reached zero together and then the lh engine shut down!!!Also, if you want to see something else interesting, try a visual circuit and landing on one engine - to touchdown well simulated but then try taxying back to the gate on one engine.RegardsJohn

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Why would you fly with the crossfeeds on in the first place? Thheres no need to. And the .4 fuel left in the center tank is normal. In fact, on shorter range flights, such as New York to Europe, the center tank doesnt have any fuel. I havent had the problem with the fuel imbalance. And I dont use the crossfeeds since they arnt needed in normal operation. If your going to do a long flight like that, leave the crossfeed off.Good luck with your problem,Brian

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BrianAgree - I do not see how Sheahan got his original problem. Even with the crossfeeds on, fuel should be used fairly equally from each engine. But investigation of his original thread has raised the question of exactly what had been modelled in the fuel system?In normal two engined flight, the system appears to operate as expected but once we deviate from the norm the system appears very illogical - the most serious practical example would be the case of a fuel leak from one side. It appears that, once the tank on that side empties both engines will quit whatever the crew do. Not very nice if you are half way across the pond!!!RegardsJohn

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Norman,Sealant failure, union failure, splits in tanks, etc etc usually through fatigue failure of some kind due to the continual flexing of aircraft components during flight. The inspection regimes which take into account the number cycles and component lifing are designed to overcome such failures - but they do happen. If there are any airframe engineers on the forum I am sure that they would provide a more authoritative comment. Similarly, I doubt that the real world 777 has the anomalies noted in this thread - particularly in single engine operation - but I stand to be corrected if any of our 777 operators are watching this.But I agree that this is all very esoteric, although interesting in seeing just how far the gauge programmer had gone in reproducing the performance of the actual fuel system. As I said earlier, in two engine, long range operation with no failures of any kind, the fuel system modelling is very effective.RegardsJohn

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I dont think norman was asking how a fuel leak could occur in real life, i think he meant how a fuel leak could occur in FS9.Brian

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