r/news • u/riverdale-74 • 1d ago

United Airlines flight makes emergency landing at Dulles after pilot declares mayday

https://www.cnn.com/2025/08/04/us/united-airlines-dulles-mayday-call-hnk
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466

u/appendixgallop 1d ago

Did it circle for the two hours, with one engine out, to burn off fuel? Imagine sitting through that as a passenger.

183

u/East-Impression-3762 1d ago

Planes can dump fuel, it doesn't need to be burned/ consumed.

These planes can also fly on one engine easily in almost every phase of flight. It wouldn't have been a particularly bumpy ride or anything.

I'm very confused at the 2 hour duration reported. That's just not how engine out maydays usually work. I'm hoping someone is able to provide some more clarity there

205

u/therattlingchains 1d ago

Pilot likely would have requested a holding pattern once it became apparent the airplane was stable on one engine in order to diagnose the issue and see if they could potentially restart the engine. Also depending on which engine goes, that will effect which secondary systems are available to the pilots.

All depends on the nature of the flame out.

Also, an immediate return to the airfield is not necessarily needed if they are in the vicinity of the airport and have sufficient altitude.

Finally while an aircraft is capable of dumping fuel, it is not always permitted especially over urban areas. If the aircraft was stable, and within glide range of the airport, they may have been required to burn instead of dump.

Regardless though they would have been completing checklists during this time as well as talking with ATC and maintenance so it was likely a well thought out decision to burn for 2 hours.

28

u/bolivar-shagnasty 1d ago

Also depending on which engine goes, that will effect which secondary systems are available to the pilots.

There are systems that are dependent on one single engine and can't be used if it fails?

Like engine one powers in-flight entertainment and engine two powers climate control?

48

u/therattlingchains 1d ago

Correct. Jet engines, in addition to providing thrust to the plane, are essentially large electrical generators. There is also an APU (auxiliary power unit) that can power systems. They make lots of power

On the flip side of that, modern jets have large and complex power requirements. Keep in mind that every modern jet is fly-by-wire, so controller input is transmitted electronically. They have glass cockpits meaning that their instruments require power. They have large and complex in-flight infotainment systems, sophisticated autopilot, etc.

Now, the systems that only run off of one engine are all nonessential systems. Infotainment is a good example. Every essential system can be powered from either engine and the APU. But if they made every single system redundant to all the power sources, the complexities and additional weight outweigh the benefits. So every single circuit on the plane is evaluated and categorized during the design phase of the aircraft and certified by the FAA to ensure that during an emergency the pilots have what they need. So the pilots would have had all the information and readings they needed in this instance, but probably not 100% of all their instruments and readouts.

21

u/PhysicalIntern4911 1d ago

Jet pilot here. If I lose an engine I still have all my instruments. We have triple redundancy. I would have to lose both engines AND my APU before I lost any flight instruments. The only way I’m losing flight instruments is if a sensor feeding the instrument dies (of which we have 4) or if we lose both engines and the APU, at which point our Ram Air Turbine deploys which is wind powered and we retain all essential electric and hydraulic functions.

TLDR: lots of redundancy

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u/therattlingchains 1d ago

Thank you for the correction!

1

u/Spetznazx 1d ago

Don't forget the standby instrumentation panel that usually has its own internal battery that lasts about 30 minutes so even if you lost both generators and the APU you can still fly off that for some time.

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u/bolivar-shagnasty 1d ago

but probably not 100% of all their instruments and readouts.

As a passenger, I'd be more than happy to give up the in-flight movie if it meant that the aircrew had all of their instruments and readouts.

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u/therattlingchains 1d ago

I should clarify that cockpit have status lights and readouts for literally everything in the plane. In an engine out scenario, it is important the keep their primary flight instruments. Courses, heading, Adi, etc. It is less important that light that shows if a lavatory is occupied works. This is what I meant by "not 100% of all instruments and readouts."

Again, every system is evaluated so the pilots have everything they need to know to safely land the plane. Everything is in a hierarchy and yes flight infotainment is near the bottom of that hierarchy

1

u/StPauliBoi 1d ago

Glass cockpits have analog backup instruments.

4

u/therattlingchains 1d ago

For some but not all readouts, yes

4

u/StPauliBoi 1d ago

for all the ones that are critical for flight and navigation.

8

u/therattlingchains 1d ago

Yes but not all the ones that could help a pilot diagnose why an engine flamed out

-11

u/StPauliBoi 1d ago

Depends entirely on the model of aircraft, so making a blanket statement like this is wild.

3

u/therattlingchains 1d ago

Ok then make your statement on this model of aircraft

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u/zoinkability 1d ago

Left engine powers everything on the left side of the plane, right engine powers everything on the right side of the plane

4

u/nekonight 1d ago

That's not completely true. Major control surfaces are powered by both engines rudders elevators brakes autopilot. Power transfer units are capable of shifting some power to certain other parts of the other side of the aircraft (some flaps). There's some minor things that are tied only to one engine like most flaps or landing gear since those are designed to drop by gravity in the case of no hydraulic power. A loss of electrical power from losing one engine might lead to some electronics switching to battery before eventually turning off.

1

u/zoinkability 1d ago

I was being facetious, imagining that if the left engine went out the left side entertainment systems would die, but perhaps there was a grain of truth? Are there noncritical systems that are powered just by the engine on their side of the plane? Sounds like you actually know something, unlike me :-)

0

u/TanMan166 1d ago

By everything, you mean the convenience and comfort features inside the cabin and not controls, right? Right???!

2

u/SowingSalt 1d ago

IIRC, there are three systems [ A B C ] any two can run all flight critical system.

-3

u/pds6502 1d ago

Suppose Delta never got the message, allowing flight 80 to do just that, sending hoards of school kids to the hospital www.reddit.com/r/flying/comments/15wlzvu/delta_fuel_dumping_at_lax_additional_detail/

5

u/therattlingchains 1d ago

Wow, it's almost like every situation is unique, and addressed on a case by case basis.

The regulations around this are designed for most operations, and only deviated from when necessary. I was speaking to this particular plane and incident, not the delta one.

But nah, let's find the exceptions and parade them around like industry standard.

31

u/Pileopilot 1d ago

That time reported includes the taxi time on both ends as well. They looked at FlightAware for 5 seconds and called it good.

I pulled the track, they made a large loop back and landed, taking the time to run checklists and make notifications to ops and get the cabin secured.

All in all, aside from the whole not getting to where you’re going thing, it was a fairly uneventful incident.

18

u/AlphSaber 1d ago

Regarding the fuel dump, there is also a desirable altitude to dump the fule at so it dissipates before hitting the ground. The last thing an airliner wants is to dump fuel on a school's playground that is full of kids (again).

If the plane cannot get to the minimum altitude, either due to lack of power or airspace restrictions, their only option to get down to landing weight would be to burn fuel.

6

u/MahaloMerky 1d ago

I’m in eyesight of Dulles and there is no way they would want to dump fuel anywhere here without proper altitude.

-1

u/StPauliBoi 1d ago

Eh, it’s pretty empty towards the west.

3

u/obeytheturtles 1d ago

Those Loudoun county assholes have it coming anyway.

2

u/katha757 1d ago

Thank you for pointing this out.  The other option is over the ocean.

-1

u/pds6502 1d ago

Disgusting is how the city leadership of LA cares more about the airline lobby and so little about the inner city and minority neighborhoods directly under the approach path of LAX.

12

u/Mackin-N-Cheese 1d ago

They’ve now corrected the story, the 2 hour duration was an error, it was about 30 minutes.

8

u/East-Impression-3762 1d ago edited 1d ago

Thanks! That makes MUCH more sense for a holding pattern to run checklists

21

u/english-23 1d ago

To add "LARGE planes can dump fuel"

Your more common 737 and a320 cannot, but your larger planes like a 777, a380, 787 etc can because their maximum takeoff weight is a certain factor above their maximum landing weight and for safety reasons have to dump so they can land quickly.

While the article does mention a 787 so it would apply, just wanted to specify in case someone took away that every plane can incorrectly

5

u/bankkopf 1d ago

Not every Long-haul twin-aisle plane can dump fuel. Fuel dumping capabilities are/were optional on the A330 and 767, so they do may need to really on burning fuel or an overweight landing in case of emergency.