Good job, SSgt Bartek Bachleda!

Hear, hear! That is a tough situation for the cabin crew; they probably hear so many passengers report "problems" that it becomes easy to ignore it. Fortunately, SSGT Bachleda pressed the issue. I also wonder why the flight crew didn't notice the loss. The fuel gauges should have shown it, and the plane should have become right-wing heavy.

That's a big "Job Well Done" for the man.

I thought that article says that crew was wondering why they were losing fuel, but didn't know why?

You're right! My miss.

Likely their' instruments were telling them that the wing tanks had a lot less fuel that engine consumption would explain but the thought that fuel was dripping out of the tank was not being grasped. Fuel can't just leak out can it?

When the gauges started indicating a loss of 3 tons of fuel per hour, they probably started planning an emergency divert. SSGT Bachleda's observation would have sealed the deal.

It depends on the aircraft. Some FMS systems have sensed (weighed) fuel on board from each tank. Others expect a manual entry from the flight crew.

However, at present most aircraft determine their fuel usage through fuel burn via the fuel supplied to the engines. The rate is usually in PPH or pounds per hour.

Lately, and this is true on the new FMS I am helping to develop, there is an attempt to detect fuel leaks when the fuel cannot have been burned and the sensed fuel does not match the calculated amounts, the system would then alert the flight crew. It's not easy to do, but I think it is worth it especially on larger aircraft where more lives will be saved with such a system. The reason it is not easy to do, is largely because it becomes complicated to determine where the leak is occurring, before the fuel pump, or at the fuel pump. It requires the FMS developer to have access to a lot of information from the airframer, the engine/FADEC manufacturer, and the fuel pump manufacturer as well.

Presently, in deployed FMS fuel management systems, this capability doesn't exist. But if a fuel leak does occur, I suspect the auto-flight system would start trimming the control surfaces as far as it could compensate and then decouple if the FMS could not automatically reroute fuel to balance the aircraft. It really depends on the specifics of the listed aircraft systems and EICAS alerting in this instance.

Brasidas, I was hoping you would check in with that exact sort of information. I thought such "predictive" capability was already built into modern FMS systems. There are many more variables than I realized.

The temptation to ignore an apparently faulty gauge can be strong. Modern flight deck procedures are supposed to prevent this, but the urge to "continue the mission" can be very tough to resist.

I've integrated about ten different FMS systems for civil business aircraft, and tested more than fifteen, some in revenue passenger airframes. My knowledge is by no means comprehensive, however, it is sufficient to produce a general impression of what the state of the art presently consists of. At present, the system I am working on developing has quite a bit more computing power than previous systems. It is also much more complex than previous systems. It will also give the pilot an immense amount of control and attempt to offload some of the detail work through procedural automation. Ironically, I find that the highly capable architecture of the future is being limited more by a lack of understanding of the architecture's capability from the system requirements authors rather than the system designers. This has led to a system capable of producing triple back-up data to single nodes of failure through poor understanding of parallel data distribution.

At present, the future functionality I foresee for next generation FMS are RTA or required time of arrival, as well as RNP 0.30 with one GNSS constellation, and RNP 0.10 with two or more GNSS constellations in place. Additionally I foresee predictive FMS tracks via ADSB-C along with common implementation of CPDLC in the very near future. This will of course be enabled by detailed improvements in next generation FMS applications along with upgrades in VHF Comm and associated digital networks on aircraft to enable these advanced functions.

The reactor operators at Three Mile Island would likely confirm such an observation.