What caused this 767 diversion?
 

Airline de-identified.

"a B767-300 operated by XXXX Airlines was conducting flight 938 from the US to London Heathrow,UK (EGLL) with 11 crew and 178 passengers. While in cruise at FL350 and passing 58N and 050W the crew observed an EICAS "Low Fuel" caution message and noted a fuel imbalance. The EICAS message cleared but the imbalance remained. The crew consulted with both maintenance and dispatch, declared a MAYDAY and diverted to Keflavik Intl., Iceland (BIKFK). Ground maintenance checks found no fuel or fuel system issues. The aircraft was refueled and departed for destination after a several hour delay."

If it helps anyone with the search, flight was UAL938 KORD-EGLL on 24th March this year.

Seems like a sensible decision, but perhaps a "Mayday" was a bit of overkill? That depends on the fuel state of course.

If nothing was found on the ground I'd suggest it was probably a transient Fuel Quantity Indication ( "gauge"/sensor) problem. Have had an instance of that, once v briefly, on descent. I suspect mid Atlantic it would get your attention. ..

Excellent decision. Excellent Company back-up & support. Mate of mine had a similar case but not oceanic. Company nearly beat him to death for making, under similar circumstances, the very wise decision to make a cautionary diversion to a Company Maintenance Base. Indeed, the dysfunction Head of Training claimed that the decision was "appalling". Mate walked away changing his cowboy outfit for much more professional garb.

It would be interesting to know if the imbalance came with the need for lateral trim.

Sounds like a good decision to me, I wonder what ‘head of training’ thoughts would have been if you end up in the drink....

Well if you remember Azores Glider story started basically almost like that: crew observed an EICAS "Low Fuel" caution message and noted a fuel imbalance.

Like I said, it depends on fuel state. What you KNOW about the situation. I wasn't there, and I'd be the last person to criticise a captain's decision, having put out three maydays myself.

More important what you don’t know about the situation. Assume the worst for every unknown factor. With Mayday you get the attention of ATC and you don’t have to fiddle around with clearances if the situation went south quick.

What you know and what the actual facts are could differ greatly..

https://en.wikipedia.org/wiki/Gimli_Glider

https://en.wikipedia.org/wiki/Air_Transat_Flight_236

Self Preservation
 

A well developed sense of self preservation is what caused this diversion. It's a good example of why us SLF types are very happy to have a couple of live human pilots up front.

I seem to have opened a can of worms with my comments. Again I say that I am not criticising the captain at all. I wasn't there, I don't have the information they had. I merely suggested the mayday might have been an overkill. However, again, if the captain decided it was warranted, then I'm the last one to argue with that.

Ref the diversion, not the Mayday.

A well developed sense of self preservation

"When in doubt there is not doubt." sometimes, especially in the middle of nowhere.

In the case under discussion here (Incident: United B763 over Atlantic on Mar 25th 2018, fuel imbalance and fuel low indications) the crew is reported to have taken the time to consult with maintenance and dispatch befose declaring MAYDAY and diverting: that consultation should have forestalled any criticism from United's Head of Training!

As Herod correctly says, we don't have the information that the crew (and maintenance and dispatch) had. We only have the AvHerald report. We don't know why the crew decided to call MAYDAY, which could have been for a perfectly valid reason.

"but the imbalance remained"

what does this mean? does it mean the individual tank indications indicated an imbalance?

who in their right mind would continue a flight under those circumstances? who would advocate it?

or, am i missing something?

Then why did you feel it was ok to make any kind of judgement? Let the facts drive you towards your conclusion, not uninformed opinion.

This is also a rumours (and that comes with speculation) forum :)

Thanks for the responses. It would be nice to have more info to see how the good decision making process was made. But of course, that is unlikely.

Keeping in mind that the original report may not be exactly correct, what does the QRH for the 767 say for a "Low Fuel" EICAS message. On my similar looking type, "FUEL QTY LOW" means that the fuel quantity is low in a main tank.

Would it be normal at this point in a flight for a main tank(I am assuming that this is one of two wing tanks) to have low fuel quantity in a 767? Sort of sounds like an actual it could be a real leak if a main tank quantity is low in mid-cruise. But there was no fault found. So how would a main tank quantity become low.

As you can see, no direct knowledge of the 767 on my part so the questions may not make sense.

With a normal fuel load and no malfunction a scenario where you might get a LOW FUEL with an imbalance is leaving the crossfeed valves open.

Over time one side inevitably has more boost pump pressure than the other and an imbalance occurs much faster than with the crossfeeds closed (or so I'm told ;)). However, you should get a FUEL CONFIG when the imbalance reaches 2200 pounds, normally well before you get a LOW FUEL when the useable fuel drops below 2200 pounds in either main tank.

One time where weird stuff seems to happen with the 767 fuel system is when somebody decides to balance the fuel. United demoed a double engine 'roll back' out of Maui in 2001 and got to check the RAT auto-deploy feature at sunset as they limped into Kona for an overweight landing. Somehow all of the main tank pumps were switched off after fuel balancing on climbout. The DEN ground school lesson on suction feed has now been updated. The star-crossed plane was N666UA but fortunately Captain Luck was in command. :ok:

The fuel gauges on the '76 are on some odd ground service bus that I think is used to run 400 Hz vacuum cleaners. I had a jumpseat rider come up to the cockpit and plug his cheap knockoff computer charger into one of the covered AC service outlets without telling me. We were about to go feet wet for a crossing. The fuel quantity gauges went to dashes and half of the landing gear lights started flashing. As I pondered my own overweight landing options, the goofball sitting behind me said 'Look, it quits when I unplug my computer!' :ugh:

I don't know if it was the fake Dell adapter or maybe the tight plug pushed wires together behind the panel.

There is also a microswitch in the fueling panel door out on the wing that sometimes can cause problems with the fuel indication. There is some trivia question about that on the oral but it's been a long time since I got the rating.