Plane Answers: Loud bangs, crosswind landings and F/A ‘crosschecks’

Welcome to Gadling’s feature, Plane Answers, where our resident airline pilot, Kent Wien, answers your questions about everything from takeoff to touchdown and beyond. Have a question of your own? Ask away!

Ruthann, who’s my proofreader for Cockpit Chronicles and this column asks a question about her recent Delta flight across the Atlantic:

About 15 or 20 minutes after departure from Shannon, there was a loud thump/bang/shudder. Not like an explosion or anything, but more mechanical, something falling/moving/colliding. We were sitting in row 26, right over the wing centre, on a 757-2.

Initially I thought, did we just lose a panel? But then I assumed it was more likely to be cargo shift. Something heavy. We were climbing at the time of course. It felt like it was right below us, or very close, but I’m not sure what the cargo layout is near that section with central fuel tank, etc?

My nervous-flyer mother had her headset on listening to music, but still heard it and wasn’t too pleased. Luckily, I don’t think she heard how loud it was. It bothered some other passengers, who asked the flight attendants, and I guess they mentioned it to the captain.

He made an announcement saying it had just been sudden, unexpected turbulence. He put on the seat-belt sign, but of course there was no sign of turbulence. It was just one single thump, but I don’t suppose they heard it up front, either way.

I had hoped to look at the aircraft when we landed to see if it could have been a panel, but it wasn’t possible to see out of the airport terminal.

Is noisy cargo-shift common? What else could it be? How often do panels fall off/pop out? Can you hear them go from inside the cabin?

I assume the gear had been up too many minutes to blame any issues there, and I’m sure if there had been a problem with that, they would have mentioned it before approach/landing, wouldn’t they?

How much do pilots not tell their passengers? Where do you draw the line? Do you ever get semi-decent ear/eye-witness reports from those in the cabin? Do you appreciate them? Remember the lady who failed to mention the little crack she spotted on boarding Aloha 243?

Thanks Ruthann,

It’s really hard to know what could have caused that issue. A cargo shift is a possibility, but that’s more common on takeoff than during the latter stages of climb or cruise. Also, the cargo area on a 757 is well behind the wing or in front of it.

You may have heard something related to the hydraulic system, since that’s often a noisy component found in the wheel well below your seat. It’s always possible that you blew a tire, which could have been caused by a dragging brake that causes an excess of heat to build up on the wheel, although if it were hot enough, we’d have an indication of that as well.

It could have been a panel as well. There are air conditioning pack doors which have been known to come off and cause a good deal of noise. Most other panels that go missing, however, would be hard to hear from the cabin.

We have warning lights in the cockpit for entry doors, overwing emergency exits and the overwing doors that hold an emergency inflatable slide. So if any of those were to open, the pilots would have an indication up front. Generally, if it’s not threatening to the aircraft, then we don’t have a warning for it.

If there’s no indication up front of an issue, we’ll likely continue the flight. But it’s always a good idea to let a flight attendant know if you hear or see anything. It’s usually not an issue, but we’ll take it seriously. We’re often informed by passengers of flap track fairings that shake a bit or something that looks like a loose screw over the wing.

This information is easy for us to pass along to maintenance, who are required to look into the issue. Under certain circumstances, it could be valuable information. So it’s definitely appreciated.

As for what we tell the passengers, I can say wholeheartedly that we don’t lie. There are times in an emergency where it’s not possible to talk to the people in the back for a while, since an abnormal or emergency checklist can take a few minutes to go through. But there’s little incentive for us not to tell the truth. This applies for delays as well as mechanical issues.

We’re taught to be straight up with passengers and to use as much detail as we feel is necessary to describe the delay or problem.

Stephen asks:

I’ve always wondered, as an airplane taxis out for departure, there always seems to be a PA announcement for the flight attendants to “Cross-check.” What does this mean?

You’re actually hearing that just before the airplane leaves the gate or just after it arrives. I figured I’d let Heather Poole, our resident flight attendant, shed more light on this PA:

When you hear a flight attendant say “cross check” over the PA, they’re letting the flight attendants in other cabins know their doors are armed or disarmed. Arming and disarming has to do with the emergency slides. When a slide is armed, it will automatically inflate after a door is opened from the inside. Since we don’t want that at the gate, the slides need to be disarmed after we arrive.

So we’re attaching the slides to the door on taxi out, and then detaching them when we’re parked at the gate, using the words cross check to inform each flight attendant that the slides are either armed or disarmed as appropriate.

Thanks Heather!

And David asks:

Often times I see on TV the landing of a large passenger plane, from the rear angle; the plane moving away from the camera, and the plane seems out of line with the center line of the runway.

How many degrees can the nose gear be “off-center” to cause a problem? And what does it feel like?

Good observation, David. I’m convinced that camera crews and editors wait for the worst possible landing to show in a movie. Maybe it’s just an effort to add a dramatic flair to the film.

But what you’ve noticed happens during a crosswind landing. The goal in landing most airliners in a crosswind is to align the airplane with the runway at the last minute using the rudder. Opposite aileron will be needed to prevent the airplane from rolling in the direction of the rudder. This is something that applies to small planes as well and it’s learned during primary flight training.

When you see the airplane touch down in what we call a crab–slightly sideways to the direction of the runway–it means that the pilot didn’t use enough rudder (or even too much) to get the plane perfectly straight.

On the newer 737s even a degree or two off will turn what would be a good landing into a real ‘thumper.’ It’s part of what makes landing an airplane a lot like playing golf. There are just so many variables that need to be accounted for to get a nice approach and landing.

At least it keeps the job interesting.

I’ll leave you with this video demonstrating just how much of an angle the airplane can be off during a crosswind landing that probably shouldn’t have been attempted:

Do you have a question about something related to the pointy end of an airplane? Ask Kent and maybe he’ll use it for next Monday’s Plane Answers