Sunday, April 3, 2011

Skylight on Southwest Flight Not Unique

Yes, I'm trying to take a few days off for fun before the beginning of the European Society of Air Safety Investigators conference in Lisbon, but what could I do when I saw the news story? Another aging Southwest Airlines 737 pops a hole while at cruise altitude? A skylight in an airliner is bad enough the first time.

Friday evening, while at 36,000 feet, Southwest Flight 816 from Phoenix to Arizona developed a suitcase-sized tear in the upper fuselage about 45-minutes after takeoff. The hole was big enough to bring the cabin altitude, normally maintained by the pressurization system to around 8,000 feet, to above 10,000 feet in 45 seconds. This causes the passenger oxygen masks to drop. But even when passengers quickly don them, it can also cause a lot of discomfort. (Read more than you'll ever want to know about depressurization events on 737s here.) 

A passenger and a flight attendant lost consciousness. In the meantime, the pilots began a twice as fast as normal descent (4,000 feet per minute) to get the plane down to 11,000 feet before heading for a military base in Yuma, Arizona where they made an emergency landing.

This event is especially creepy because less than two years ago, I reported on a similar scenario on another Southwest 737-300. B.N. Sullivan's blog Aircrew Buzz has a fairly detailed explanation of what NTSB investigation revealed which you can read here.

As might be inspected when your airline is hit with this kind of can-we-say-nightmarish-publicity, the COO of Southwest is eager to suggest that this second fuselage-ripping event is in no part due to any lapse or action of the airline. Nope, Mike Van de Ven says Friday's episode is baffling even Boeing.  

Mike Van de Ven Southwest Airlines photo
In a statement, Van de Ven says, Boeing has identified an inspection program and "based on this incident and the additional findings, we expect further action from Boeing and the FAA for operators of the 737-300 fleet worldwide.” Well Southwest doesn't fly outside of the U.S. yet, so that "worldwide" is supposed to lead us to conclude the problem is bigger than Southwest. Well maybe it is.

But really, how do you say this with a straight face? "What we saw with Flight 812 was a new and unknown issue." Say what?  The effects of age on aircraft structure burst onto the scene quite literally twenty-three years ago when Aloha Airlines Flight 243 lost 18 feet of fuselage during a passenger carrying flight. This dramatic event, in which a flight attendant was killed after being sucked out of the airplane, launched the air safety regulators on long-running and multi-faceted investigations into operation, maintenance and inspection of airliners as they age.  For five years, I participated on the FAA's follow-on committee which expanded on structures to include the effects of age on aircraft systems. But I digress. 

The fact is that while many airlines have been replacing older model airplanes, they still represent a sizeable portion of the all-737 Southwest fleet. And, if you're looking for an airpline that rides them hard, you need look no farther than Southwest. Short haul flights and extra fast turn around times at the gate mean, according to Patrick Smith of Ask The Pilot fame, that Southwest Airlines has one of the highest airplane utilization rates in the industry.   

As of day two of the grounding of 300 Southwest 737s the airline has found "small, subsurface cracks" on two of twenty-one planes using a testing procedure not previously used on airplanes for this kind of detection, as far as I can tell.  That may be the "unique" referred to by the Southwest boss.  

If high frequency eddy current testing can detect invisible cracks that will be another positive development in the ongoing effort to maintain the integrity of older airplanes. But Southwest and other airlines with demanding operations would do well not to forget that aging fleets require special care and there's nothing "new and unknown" about that.


Nikos said...

You are quite correct to say "not unique" - aluminium cracks...

I applaud the Boeing fail safe design integrity of the 737 cabin structure!

Arjen said...


Thanks for this article, excellent written.
Mission first, safety always!

Cindy Richards said...

Nice job, Christine. I wanted to let you know that I linked to your post from one on