Fuel Load Question for the Big Boys

kontiki

kontiki

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Kontiki
What do airline pilots do to ensure they have enough fuel on board? I'm guessing there must be some kind of reality check. Do they just trust the Fuel Quantity Indication system at each departure? I can't believe they stick it each time.
 
The get a fuel slip from the fueler after fueling. The pilot then checks against what the dispatcher calculated.
 
The fuel gauges are very accurate and the fuel flow/burn is also. When we initialize our ACARS it shows fuel on board from the previous flight and current fuel on board. We put in how much was added by the fielders and if there is a discrepancy it lets us know.

Only once, when a fuel gauge was inop, do I recall them draining a tank and then having to fuel the aircraft so that we had a known quantity on board.
 
Busflyer said:
The fuel gauges are very accurate and the fuel flow/burn is also.
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Agreed. We actually rely on our gauges. Our military flight planning software is pretty good and a little "padded." Always end up landing with more than the plan said you would. Plus I know ballpark it is around 18,000 lbs/hr when doing a local training flight and about 13,000-15,000 lbs/hr in cruise. I make sure I or the Flight Engineer monitors the fuel state along the flight. Same techniques you do in a small GA plane, but the quantities and burn rates are larger.
 
As others have said the gauges are very accurate, and if there is a flow problem we can even put a flow correction into the FMS. The dispatchers do fuel planning which we have the release for that takes into account all the variables and we typically land within a very very close margin to what they planned us to land at since planning software is extremely accurate (assuming no large route changes or delays). we have a gate fuel number and a minimum takeoff fuel number. For us on my equipment we need to be within +/-300lbs of the planned gate fuel prior to push back and for takeoff we need to be at or greater than the planned takeoff fuel number.
 
Funny you bring this up. We just changed our fuel verification procedures due to an incident late last year where one of our airplanes landed WAY below minimum fuel due to a fuel gauge/fuel LO warning malfunction. It could have been REALLY bad. They were lucky. Now we have to compare our actual block in fuel with the planned block in fuel, and then again before takeoff, we have to verify the last flight's block in fuel and then add it to what the fuelers said they put on to ensure that the gauges are correct.
 
All of us who sit in the back of those heavies hope whatever you are doing the numbers add up :cool:

"Gimli Glider" Air Canada Flight 143

 
Sadly having a fuel gauge problem isn't that uncommon on my plane. We can even go with an entire fuel gauging system inop...it gets rather involved after that. The system uses very accurate fuel capacitance measuring with redundancy. There are two sending units in each tank that feed their data to a sending unit which sends it to the Fuel System Controller and to the Flight Management System. Sounds fantastic and it is when it works. The fuel is being moved around automatically to maintain the most efficient CG, keep it from freezing etc. If it says we will land with 20000 lbs, we will.

Now, in my description of the system I described how it works perfectly but engineers (necessary evils like lawyers because they think they know everything) say that we have two tank sending units (transducers) and the data from each are used at various times...great so far...but their data is sent to ONE sending unit. If a fuel sensor transducer fails and it is the one that the sending unit is using, it now senses ZERO fuel. Computers being what they are now tell the airplane that you are out of fuel and weigh about 50K lbs less. What happens? Throttles come to idle, all kinds of warnings go off and crew members are saying "WTF over". Then a few seconds later the other transducer kicks in and instantly adds all the missing fuel weight back into the computer and the throttles go up and it continues on. How do we shut off a bad transducer? Can't. Douglas/Boeing says this cannot happen. Happened to me...at night...800 miles off the coast of Ireland. Shannon has a very nice hotel. BTW, we shut off the auto throttles and just flew but the up and down on weights and speeds continue all the way to touchdown. On final it was giving us an erroneous speed and if we had followed the flight directors we would have ground the tail down considerably. Normal landing attitude is about 4 degrees up and it was telling us to fly 12 degrees up.
 
I own a little Grumman Tiger. The first and probably only airplane I ever own. It has an electrical resistance/float gauge that I don’t trust. It also has a 3rd party fuel flow system that was dead nuts accurate last time I checked.

The last time I drained a tank to seal a few plates, I bought a universal gauge, leveled the aircraft, added fuel about 5 gal at a time, and worked up a calibration curve for the stick. That stick is truly the only thing I trust for making sure I’m taking off with the right fuel.

I started the thread because I wondered if airline pilots really weren't really at a disadvantage when it comes to knowing they are taking off with the right fuel. I think I have my answer.
 
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Sight guages almost never lie. How can they? You are looking at the actual fuel!
 
Dispatch order the fuel, our flight plan shows total fuel onboard, minimum required for takeoff and a breakdown of how that load was built (fuel for taxi can be many hundreds of pounds at a busy airport like DFW or ORD) Reserves can be added for enroute turbulence and they often add 'Ferry Fuel' for perhaps a very early start, quick turnaround or because its much cheaper somewhere else.
There is a line for 'Captain Add' fuel. Thats if we've ordered more than dispatch. They may as us why, but it's never a problem. My aircraft is seldom weight restricted even with full pax.
We put the min takeoff fuel and flight number in the FMS so it appears on one of the EICAS screens -3756 125 means flight 3756 with a minimum fuel for take off of 12500lbs; and this is one of the final before takeoff checklist items.
The fueling truck simply shows up; plugs in and programs the Fuel Computers with the required load; the FCC manage the distribution of the fuel for ZFW and balance. We can't pressure fill the beast without the gauges.
For perspective and laughs, our APU burns around 100 gallons an hour..
I regularly see Gimli out of the window. Always do a fuel check :)
 
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kontiki said:

I started the thread because I wondered if airline pilots really weren't really at a disadvantage when it comes to knowing they are taking off with the right fuel. I think I have my answer.
Click to expand...

We used to get the fuel slip before push - I could see how many gallons were pumped into the airplane and use that as a way to check the gauges. They've since taken the fuel slip away, so the gauges are all I have now. As others have said, they're crazy accurate and I trust them, but yeah, if for some reason they were incorrect, I wouldn't know. If there's any question, I can use the drip sticks, but that's something that generally only happens within the context of an MEL.
 
I believe I've been told that the un-reliability of a commercial jet has to be less than 10^-18 (I don't have a reference for that).
The interpretation I understood (again no reference) was that it meant; airplane equipment failures sufficient to render the aircraft un-flyable or un-landable during the course of a single flight would occur no more than 1 time in 1,000,000,000,000 flights. I'm also under the impression that no single human can work to the 10^-18 number (been told that, again no reference).

It seems to me that even if you build an aircraft that reliable, the process for ensuring sufficient fuel at every departure also needs to be at least that good for the results to be predictable. Nowadays there is a lot of economic pressure to put less fuel on things. That means bean counters and all sorts of half trained self styled efficiency heroes come into the picture. Does anyone do a formal numeric system safety assessment of fueling processes for an airline and come up with a reliability number?

No fuzz on it, I wouldn't pretend to know where to start, I'm probably overloading my butt when I get into this stuff.
 
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