There’s a story that has gone viral regarding United’s October 2 flight from Los Angeles to Sydney, UA839, which landed early this morning (October 4). The pilot declared a “mayday,” which is a distress signal generally used for life-threatening emergencies (less urgent situations will receive a “pan” call).

I’ve seen a lot about this in US media, but it seems that this story went even more viral in Australia, where it has made national headlines. For example, check out this news clip in Australia, which comes across as rather sensationalized. They even interview a passenger who just got off the flight to get their take on it (even though they had no clue there was any sort of an emergency).

So, what do we know about this situation? The total flight time was 14hr5min, which is no longer than usual. The flight wasn’t even full. A 787-9 has the range to fly much longer than that. For example, this is the same plane that United has used to operate their flight from Los Angeles to Singapore, which is a couple of hours longer.

Here’s the ATC audio of some of the “incident:”

So this raises a few logical questions:

Why didn’t the United plane have more fuel?

Generally speaking airlines will only load as much fuel as they have to, which would be the projected fuel burn plus minimal reserves, plus a small additional buffer. Ultimately the reason they don’t always load a couple of hours of extra fuel is because it adds weight to the plane. In other words, you’ll burn more fuel just to carry the extra fuel, not to mention it may come at the cost of carrying cargo.

So it’s also possible that a 787 operating a four hour flight could have a fuel emergency, since it won’t have a 10+ hour reserve of fuel.

What caused this fuel emergency?

We don’t actually know for sure yet. Just because the flight wasn’t longer than usual doesn’t mean they didn’t burn more fuel than usual. It could have been that headwinds were stronger than expected, or that they didn’t fly at an ideal altitude.

Interestingly in a statement to Australian media, United Airlines indicated that there was a “mechanical issue” with the plane. That wasn’t communicated to air traffic control, which makes me wonder if that’s actually the case, or if that’s something they said after the fact when they realized they may have more fuel than they were expecting, and they wanted to avoid any issues with an investigation (lying about a mayday is a serious problem).

How little fuel did the plane actually have?

Based on the degree to which this story is being sensationalized, you’d think the plane had a few gallons of fuel left and was in serious danger.

Looking at the Australian Government Civil Aviation Safety Authority guidelines, here’s what it says about mayday fuel declarations:

EMERGENCY FUEL – is a situation of fuel emergency when the calculated usable fuel predicted to be available upon landing at the nearest aerodrome where a safe landing can be made is less than the fixed fuel reserve and as a result of this predicted fuel state, the aircraft requires immediate assistance.

Note: MAYDAY FUEL DECLARATION is a distress message indicating the pilot-in-command has assessed that the aircraft is threatened with grave and imminent danger and requires immediate assistance.

To further define that, here’s what the fixed fuel reserve is:

FIXED FUEL RESERVE – the amount of fuel, expressed as a period of time, required to fly at holding speed at 1,500 feet above aerodrome elevation at ISA conditions, calculated with the estimated weight on arrival at the destination alternate aerodrome, or the destination aerodrome when no destination alternate aerodrome is required, that would be useable fuel remaining in the fuel tanks until completion of the final landing.

Based on the chart further down in the same document, the fixed fuel reserve for a jet would need to be 30 minutes.

So based on that, a mayday could be called if the plane was expecting to have less than a 30 minute fuel reserve when landing. Again, even with a roughly 30 minute reserve, the plane would still have enough fuel to do another approach in the event of a missed approach.

It’s perfectly normal for planes to land with 31-60 minutes of fuel, so if they had a little more fuel we probably wouldn’t have heard about this issue.

Did the airport overreact?

Sydney Airport shut down the roads around the airport when this incident occurred. Was that an overreaction for an event like this, where a plane was making a routine landing? Yes, probably.

At the same time, a lot of situations like this are based around consistent protocols. In other words, when a plane calls a mayday the airport likely responds in the same way, regardless of whether this is a low fuel situation, or a plane with an engine that fell off.

So while that was probably unnecessary here, better safe than sorry, I guess, as there’s value in having consistent protocols.

Bottom line

The reason air travel is so safe is because of all the precautions that are taken. We have no reason to believe that anyone’s life was in danger, as the plane almost certainly had enough fuel to make another approach. The plane was more likely to just be slightly below minimums.

What we don’t know is why the plane burned fuel more quickly than expected. It could have been due to unfavorable winds, or an unfavorable cruising altitude. United also indicated there may have been a mechanical (which wasn’t communicated to air traffic control), though I find that a bit odd.

Regardless, there really isn’t much to see here, even if the airport was super cautious in closing off the roads (presumably in preparation for a runway overrun/crash landing).

As to why airlines don’t load more fuel, it’s both a cost saving and environmental thing. Airlines are pretty good at predicting fuel burn nowadays, and it’s rare that this becomes a major problem.

What do you make of this United incident in Sydney?

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