Outboard of the wing tanks lives the surge tanks. They get fuel in them if there is wing tank overfill, thermal expansion, full tank switch out of calibration/inop, etc. The vent/naca scoop for that tank may have a little fuel vent out on initial climbout. It lives close to fuel dump pipes, but different systems.

Question 2. Cold soaked fuel frost. Probably had extra gas/tankering and wing tanks were quite full on arrival with high humidity. Some planes have box marking of where it is acceptable to takeoff with depending on thickness. That is the black paint line in you pic I believe. Mostly common on bottom of wing.

1. It's likely that some fuel got into the fuel vent system and was venting overboard.

2. Looks like the cold-soak fuel cooled the upper skin and that produced some ice when you descending into the warm, humid air.

I'm always curious, after a turbulence, where flight attendants were asked to take their jump seats, the caption usually says FA please check in. What exactly is communicated?

Check in means that they can get up. The F/As then check for any issues in their area, injuries, damage, etc., if the turbulence was bad enough, then do an all-call with the purser. The purser then calls the Captain with the status of the cabin. Usually it's just, "We're good".

A little while ago I found way more information than you'd (probably) ever want to know in an excerpt from the eFAOM posted as part of a NTSB docket (DCA20CA058) for an turbulence incident involving an A320 and that announcement is the conclusion of a sequence:

I'm including the full test below because for me it really helped to control my nerves around turbulence to fully understand what is being conveyed (and thankfully I've never hard the "immediately" version)

PA: "Flight Attendants Take Your Jumpseats"
Flight Attendant Actions:

• Discontinue service and move the carts to a safe location outside of the aisle (e.g., into galley locations, jump seat-free cross-aisles)
• Proceed to a jumpseat and ensure seat belts AND shoulder harnesses are securely fastened at all times.
• Verbally advise customers to sit down and fasten seat belts. If possible, make PA announcements as necessary.
• Remain in jumpseat until the pilots make the "Flight attendants, check in" PA announcement

PA: "Flight attendants, be seated immediately. Be seated immediately"
Flight Attendant Actions:

• Stop. Stop service (i.e. angle cart into a seat and set cart brake, leave cart within galley and set cart brake)
• Drop. Immediately secure yourself at the nearest available seat (jumpseat, if immediately adjacent; otherwise take the nearest customer seat if one available). If aisle seat is unavailable, sit on the floor and hold on to a secure stationary object (i.e. seat leg brace)
• Hold On. Remain in jump seat with seat belts AND shoulder harnesses securely fastened or other secure location.
• Verbally advise customers to sit down and fasten seat belts. If possible make PA announcements as necessary
• Remain in place until the pilots make either the "Flight attendants, check in" or the "Flight attendants, take your jumpseats" PA announcement.

PA: "Flight attendants, check in"
Flight Attendant Actions:

• "Flight attendants, check in" PA announcement is the indication that it is safe to resule duties.
• Check on customers and cabin for any injuries or damages
• Proceed to an available jumpseat interphone and check in with the International Purser/Purser or designee.
• Report post turbulence findings to International Purser/Purser or designee
• International Purser/Purser checks in with the pilots for any further information as soon as possible

Thanks.

Why were two people who were NOT supposed to be in row 20 still in row 20 after the move? "Chicago" didn't know about those two as they weren't on the seat map in row 20. So W&B was still technically 'off'. Back to my point...if moving one person from row 21 affects W&B and makes "Chicago" happy, why is two people who are NOT supposed to be in row 20 acceptable?

Thanks,
-RM

Because the F/As didn't compare them with the seat map on their Link device.

There is plenty of safety margin built into the system to account for variabilities such as that. You still have to start with a result that is within the limits and correct any discrepancies that you find.

Thanks again for the reply. They had to have compared them with their device after I literally called them out and the FA looked at his device and asked them why they were there. So the need to move one person from row 21 was before the FA even realized two people were sitting in row 20 which 'Chicago' didn't know about. In my mind the two in row 20 still had to be moved back to their original seats because that's what Chicago had planned for the W&B of the flight. Seriously not trying to split hairs. We took off and landed without issue. I'm just curious why two people were allowed to stay in seats they weren't assigned to when a person was forced to the dead last row. I do not know where the two who seat poached were originally seated; they were already in row 20 when I boarded.

-RM

I think the simplest answer is that the flight attendant(s) decided to pick their battles and not fight it; which I completely understand in isolation, but in a situation like yours, I would argue they need to be strictest in order to ensure the most accurate weight/balance.

F/As are supposed to have passengers move back to their assigned seats. I'm not sure what else you want.

I had a flight on a new A321, and we taxied to the runway using only the right engine, it appeared. I was seated on the left side and could see the left engine was not being driven (wrong word maybe). I know it can appear to not be moving or to be moving at a different speed than it actually is, but I watched it closely and I'm certain it was not running during the taxi. When we were about fifth in line to depart, the engine spooled up.

Is this common to taxi with only one engine? Is it something particular for the A321?

Single-engine taxi is routine and is done to save fuel. The engine needs three to five minutes of warm up time, depending on how long since it last few, to warm up before takeoff.

On the 737s, we start the right engine first because that allows us to run the right airconditioning pack off the right engine while we use the APU to start the left engine. If we started the left engine first, both packs would have to be off when we started the right. When I've been on the jumpseat of the A319 and A320 they started the left first and right later. I would have thought it was the same on the A321 but perhaps not.

After landing, we will shut an engine down during taxi in, for the same reason, after a three-minute cool down. The Airbus should be similar.

At heavy weights, or when tight maneuvering is required to get out of, or into, the gate, both engines will be used to reduce jet blast.

So interesting — thank you. It makes sense, that, but I must have never looked closely enough to notice it before.

And actually, about the Airbus and order of engine sides, you are right! Or maybe left. I just rechecked my boarding pass, and I was seated F side, not A side, so it was actually the right engine that was started later. Not the first time I mixed up which side I was on. 🤦 (Sorry again to all the other passengers in whose seats I've incorrectly sat.)

I'm not following why the sequence matters? Can you please ELI5?

Ditto for needing both engines to reduce jet blast.

These threads are super informative, thanks for sharing your insights.

The systems on each airplane are different so the requirements and procedures will also be different based on each airplane.

In the 737, you can isolate the left and right pneumatic systems. The APU bleed air is on the left half of the system.

We start the right engine by routing APU bleed air through the isolation valve into the right half of the system. Both packs have to be off during the engine start so that there is enough air pressure and air flow to turn the engine's starter. When the engine start is complete, we close the isolation valve and route bleed air from the right engine to the right pack. At that point we can either use the APU air to start the left engine or to power the left pack. We do the latter if we're doing a single-engine taxi.

If we single-engine taxi, when it's time to start the left engine then we'll turn off the left pack leaving only the engine starter for the APU bleed air to run. Once both engines are started, the left engine bleed air powers the left pack and the APU air, and APU, are shut off. The isolation value goes to the Auto position where it will automatically open if the bleed air fails from one of the two engines.

The Airbus systems are different and it works best to start the left engine first. I've never flown the Airbus so don't know the details.

With only one engine running, you'd need to push up the power up too high on the only operating engine if your a heavy, in a congested area, or need to make a tight turn out. By having both engines running you don't have to push the engines up so high so there is less jet blast.

At the even C-gates in ORD, for example, we also start both engines because of the tight turn and congested area behind us. If a long taxi is expected, the left engine (737) can be shutdown as soon as we clear the parking area to save fuel.