I’m sure a lot of you have been wondering why I haven’t written about the Southwest 737 that had a big hole open up inflight last week. It was big news for sure, but I just didn’t know enough beyond the basic information to make a post worthwhile. Southwest is still not saying much at all, but I was able to piece some things together from other sources to get a better idea of what’s actually going on. It all starts with a lap joint.

What Happened
Last week, a Southwest 737-300 airplane was flying from Phoenix to Sacramento when a hole opened up in the roof. The airplane lost pressurization (of course) but the pilots were able to land the airplane in Yuma and everyone was fine. You may have heard people talk about how the airplane plunged after the hole appeared, but that was on purpose.

When an airplane loses pressurization at altitude, you can’t breathe. And that’s a problem. There are oxygen masks but those don’t have an endless supply of oxygen in them. So anytime this happens, the pilots are trained to go into a steep descent until they get to around the 10,000 foot mark where the air is breathable. It may seem like you’re plunging, but it’s all part of the plan.

Once on the ground, it was easy to see that this was no small hole. It happened in the crown of the airplane along a lap joint. That’s a horizontal line where two pieces of the skin come together and are fastened to each other. As you can imagine, this area is cause for concern regarding fatigue because joints are the weakest points in a structure.

Tear Straps
The part that’s really concerning here isn’t the tear itself so much as it is the size of the tear. See, on all these airplanes, they install what are called tear straps. The aircraft of particular concern are the 737-300, -400, and -500s, collectively called 737 Classics. Next Generation (or “NG”) airplanes make up the bulk of the 737s you’re likely to fly, including all of the ones that American and Delta operate. Those had a different design and are newer so they aren’t impacted by this. I’m sure, however, that the FAA and Boeing will be watching this closely.

But back to the Classic airplanes. On the older models, these tear straps were placed every 10 inches horizontally along that lap joint. In 1993, a change was made that resulted in the straps being needed only every 20 inches. These tear straps are meant to stop any crack from spreading further. In other words, even if a hole opened up, it should never go further than 10 or 20 inches depending upon the airplane because the tear strap will stop it.

As you may have seen, this went for feet, not inches, and that means that the tear straps were breached. That is not good. So, Boeing, the FAA, and the airlines are diving in to try to figure out what exactly happened here. But for now, they are simply mandating inspections for cracks so that this never even becomes an issue. Why weren’t these being inspected before? That’s a different story.

Shouldn’t These Have Been Inspected?
For the older 737 Classic models that were built before 1993, there were directives issued that required inspections (using technology, not visual) for aircraft with more than 45,000 cycles. That was eventually lowered to only 35,000 cycles. One cycle is one takeoff and landing. This metric is used because that’s a good measure of how much stress is put on the airframe going through the pressurization process.

At US Airways media day yesterday, that airline confirmed that all of its 737s fall into this category, and they’ve been doing the inspections since the FAA mandated them early last decade. More than half of Southwest’s 737-300s fall into this category, so presumably the airline has been conducting these checks as required. But it didn’t use this as a standard 737-300 maintenance procedure for the full fleet. On those airplanes built after the 1993 manufacturing change, none of these non-visual inspections were done, because they didn’t have to be done.

With hindsight, that’s too bad, because had Southwest inspected all of its 737-300s, it would have found the cracks. The airplane that opened up a hole had more than 39,000 cycles. But the newer manufacturing process wasn’t expected to have problems this early on in the life of the airplane. In fact, Boeing thought that 60,000 cycles would have been a good conservative number for an inspection. Now, the FAA has mandated checks on these newer airplanes starting at 30,000 cycles.

So as you can see, there’s a lot up in the air. Nobody knows why cracks are showing up on these airplanes so early in life, but stepped up inspections will make sure that they are safe to fly regardless. Now the investigation can focus on why this is happening.

Qantas A380: Now We Know Why the Planes Were Grounded — and It’s Scary – BNET Headwinds
As more details on the A380 grounding come out, it becomes more clear why Qantas grounded the airplane.

Aggrieved Fliers Ask, ‘What Now?’ – The New York Times
A very small part of a much longer conversation was published in this article about tarmac delays.

How Southwest Measures the Success of “Bags Fly Free” – BNET Headwinds
Last week at Media Day, Southwest got into survey details on how it measures success of Bags Fly Free.

Airline reviews: Find out if an airline is any good – Budget Travel
Sean over at Budget Travel asked me how to find if an airline is legit or not. Here’s my response.

Southwest: Why It’s Promoting No Change Fees and Its Web Site – BNET Headwinds
Now that Bags Fly Free is working, here’s what’s next. From Media Day, of course.

In the Trenches: The Stress of Exhibiting at a Conference – Intuit Small Business Blog
I have started blogging about my experience as a small businessperson at the Intuit Small Business Blog. My first post was on exhibiting at a conference.

Election 2010: Airlines Lose Key Merger Opponent in the House with Oberstar Defeat – BNET Headwinds
Rep Oberstar, the constant airline merger opponent, has lost in the race for re-election. That’s good and bad news for airlines.

Southwest Tells Airports to Keep Costs Under Control – BNET Headwinds
Airport costs are skyrocketing, and I asked Southwest about that during a one-on-one interview with EVP Bob Jordan. He said airports do need to keep costs under control.

Qantas Grounds A380s After Engine Failure: There’s More to This Story – BNET Headwinds
The big news at the end of the week was Qantas grounding the A380 fleet. There has to be more to this.

Qantas A380: A History of Problems With the Rolls-Royce Trent 900 Engines – BNET Headwinds
This isn’t the first problem with the Trent 900 engine on the A380. Not sure what’s related at this point, but it’s worth taking a look.

I know, it’s Saturday, so you’re expecting Cranky on the Web, right? Well that’s going to have to wait, because today is not just any Saturday. It’s September 11th.

Believe it or not, this is actually the fifth September 11th that I’ve written a post, and it’s the fourth in which I’ve followed Holly Hegeman’s tradition of publishing the names of the flight crews killed that day.

So, let’s focus on those airline employees who lost their lives just doing their jobs. Please read through the following names and remember what they went through nine years ago today.

American 11 (Boston to Los Angeles)
Crashed into World Trade Center
John Ogonowski, Dracut, Mass., Captain; Thomas McGuinness, Portsmouth, N.H., First Officer; Barbara Arestegui, flight attendant; Jeffrey Collman, flight attendant; Sara Low, flight attendant; Karen Martin, flight attendant; Kathleen Nicosia, flight attendant; Betty Ong, flight attendant; Jean Roger, flight attendant; Dianne Snyder, flight attendant; Madeline Sweeney, flight attendant

United 175 (Boston to Los Angeles)
Crashed into World Trade Center
Victor J. Saracini, Lower Makefield Township, Pa., Captain; Michael Horrocks, First Officer; Amy Jarret, flight attendant; Al Marchand, flight attendant; Amy King, flight attendant; Kathryn Laborie, flight attendant; Michael Tarrou, flight attendant; Alicia Titus, flight attendant

American 77 (Washington/Dulles to Los Angeles)
Crashed into the Pentagon
Charles Burlingame, Captain; David Charlebois, First Officer; Michele Heidenberger, flight attendant; Jennifer Lewis, flight attendant; Kenneth Lewis, flight attendant; and Renee May, flight attendant

United 93 (Newark to San Francisco)
Crashed in Shanksville, Pennsylvania
Jason Dahl, Colorado, Captain; Leroy Homer, Marlton, N.J., First Officer; Sandy Bradshaw, flight attendant; CeeCee Lyles, flight attendant; Lorraine Bay, flight attendant; Wanda Green, flight attendant; Deborah Welsh, flight attendant

[Photo credit: http://www.flickr.com/photos/79493961@N00/ / CC BY-SA 2.0]

The details of the British Airways 747 near-accident in South Africa are out, and man, was that scary for the pilots. They did a great job of keeping that bad boy in the air, but it could have ended very differently. Here’s what happened.

On May 11, 2009, BA flight 56 prepared for its evening departure to London/Heathrow. Afternoon rain had cleared out and it was a clear evening with light northerly winds and temps in the mid-50s (something like -358 degrees Celsius, I’m told). Boeing 747 G-BYGA was ready to bring 265 passengers and 18 crew members back to the UK, so it was about 80 percent full. It probably looked a lot like this one (though this was in Cape Town, not Jo’burg):

Photo via Flickr user Sara&Joachim

They buttoned up and headed for the runway. Engines spooled up as usual and they started rocketing to the north on runway 3L for the long flight home. When the airplane hit 167 kts, just about the time for it to rotate, all hell broke loose. Somehow, due to a technical fault, the airplane showed that thrust reversers had been deployed. Thrust reversers deflect the air within the engine to push it forward instead of backward. This is generally only a good idea when you want to stop the airplane, so it happens with wheels on the ground during the landing rollout. Here’s what they look like on a Lufthansa 747.

Photo by Flickr user wbaiv

Fortunately, the thrust reversers didn’t actually deploy and it was merely a faulty warning, but it did bring with it some unintended consequences. When the thrust reversers deploy, the slats Krueger flaps automatically retract. What the heck is a slat Krueger flap? I’m glad you asked.

Original photo via Martin20

See those little things hanging over the front of the wing? Those are slats Krueger flaps. Like flaps behind the wing, they’re meant to help increase the surface area camber of the wing to provide more lift. When you’re cruising, you don’t want this because it provides drag and slows you down. But when you’re taking off and landing at slow speeds, it makes it more stable and allows you to fly slower. That’s good.

When it’s not good is when they retract just when you need them most. So picture a 747, just about reaching take-off speed, that suddenly loses its slats Krueger flaps because they think it’s time to retract. Lift goes away and the pilots see less and less runway ahead. Holy crap. So what happened? Well, they took off and sat at about 40 feet above the ground trying to pick up speed. It kind of looked like this:

Photo by user klever

Ok, so I lied. It looked nothing like this. Instead, replace that airplane with a hulking, slat-less 747 barely clearing the terrain below. Yeah, I’d freak out too. Ultimately, the slats Krueger flaps were back in their deployed position a mere 23 seconds after they ran away, but those were the 23 most critical seconds of the flight. The airplane then started climbing, but the pilots weren’t content to continue on. They dumped fuel and eventually returned with everyone safe.

My guess is that there might have been some people in the back wondering what was going on, but it happened so quickly that they unlikely would have had a chance to even register that this was a real issue. The pilots, however, must have absolutely flipped. Fortunately, they did a fantastic job. The pilot in command happened to have aerobatic training and was well-versed in how to fly at near-stall speeds. There’s no question that those guys saved that airplane and all the people onboard.

But it’s not just them. There was some serious luck here. Johannesburg sits a mile high, and that reduces aircraft performance. But had this been in summer instead of winter, it would have been much worse. Hot weather makes it harder for airplanes to gain altitude, so the mild temperature undoubtedly helped here. It’s also a blessing that the airplane was only 80% full instead of 100%. The added weight would have hurt. On the other hand, it certainly didn’t hurt that they had a slight headwind and the the weather was good.

Anytime there’s an accident, it always requires a handful of things to go wrong. In this case, while one awful thing went wrong, everything else went right. And that’s why the airplane was saved. One other thing going wrong could have resulted in disaster. Fortunately, that didn’t happen here and changes required by the FAA mean this particular incident shouldn’t happen again.

Update at 917p on July 9 – Thanks to the readers who corrected me here. There are no slats on the 747 but rather Krueger flaps. Wikipedia has a good explanation of the difference: