Another emergency landing: How a tiny little hole in Southwest window prevented disaster: Failsafe kicked in when outer window pane shattered on board 737-700 at 26,000 feet

By ASHLEY COLLMAN FOR DAILYMAIL.COM

The tiny hole on the bottom of airplane windows is what saved on Southwest Airlines flight from disaster on Wednesday.

Flight 957 from Chicago to Newark was forced to divert to Cleveland after an outside pane of a passenger window broke at 26,000 feet – just two weeks after a woman died after being partially sucked out of a window on another Southwest 737-700 jet.

While the window breaking inevitably caused panic on the flight, experts said that the design of the plane window meant that the aircraft was able to land safely and able to avert disaster.

Above, a view of the shattered window on the Southwest flight that was forced to make an emergency landing on Wednesday

It's still unclear what caused the window to break

On call: Emergency vehicles at Cleveland Airport after the diversion

It’s still unclear what caused the window to break. The incident that happened two weeks ago was caused by an exploding engine

The Chicago flight was on its way to Newark when it diverted to Cleveland on Wednesday

The Chicago flight was on its way to Newark when it diverted to Cleveland on Wednesday

Since only the outer pane broke, the cabin didn’t lose pressurization and the flight landed without issue or any injuries. Windows on commercial planes typically have three panes – outer, middle and inner – made of acrylic and glass.

The fact that just the outer pane broke is evidence that the window was acting as designed. In fact, it’s that little hole at the bottom of the outside pane that regulates how much pressure from the cabin is exerted onto the window and makes sure that if the window is going to break – the outer pane goes first.

‘The way they are designed, the window performed, the backup function worked as intended,’ former National Transportation Safety Board member Richard Healing told Bloomberg. ‘My suspicion is it was the outside part but the frame held and kept it in place. It performed as intended.’

Healing went on to say that passenger windows cracking is very rare and it’s actually more common for cockpit windows to break.

‘My sense is that its very rare for a cabin window to have that issue,’ Healing, who now leads Air Safety Engineering, said.

Patrick Smith, the pilot behind AskThePilot.com, told DailyMail.com that Wednesday’s incident doesn’t seem serious, and that it was probably only in the news because of the deadly accident two weeks ago.

‘It appears that one layer of the inner window pane failed for some reason. It’s hard to say why at this point, but the result was nothing serious.

‘If not for the fatality on board the Southwest flight a couple of weeks ago, it’s unlikely we’d be talking about this at all. The two incidents are completely unrelated, and this latest one is particularly minor,’ Smith said.

The plastic pane on the inside of the plane is to prevent passengers from getting access to the glass panes in the middle and on the outside.

There is a middle pane of glass with a hole in it, then an air gap, followed by an outside pane of glass.

This hole helps maintain the pressure differential and directs it onto the outer pane rather than the inner pane.

There are multiple layers of pane in each aircraft window; in this case it was the outside pane which broke, a sign, says Richard Healing, a former National Transportation Safety Board member, that it was designed correctly

A patent (illustrated) filed by Daimlerchrysler Aerospace Airbus in 1997 explained this 'air conduit' helps maintain 'external atmospheric pressure inside' the panes. If all the panes were sealed, and didn't have holes, the pressure in the cabin would act on the inside pane of glass and there would be no failsafe if it cracked

A patent (illustrated) filed by Daimlerchrysler Aerospace Airbus in 1997 explained this ‘air conduit’ helps maintain ‘external atmospheric pressure inside’ the panes. If all the panes were sealed, and didn’t have holes, the pressure in the cabin would act on the inside pane of glass and there would be no failsafe if it cracked
The little hole at the bottom of the outside pane (stock image) regulates how much pressure from the cabin is exerted onto the window and makes sure that if the window is going to break - the outer pane goes first, which is what happened in this case

The little hole at the bottom of the outside pane (stock image) regulates how much pressure from the cabin is exerted onto the window and makes sure that if the window is going to break – the outer pane goes first, which is what happened in this case

Despite the assurances from experts, passengers were nonetheless terrified.

Linda Holley texted her son that the window broke and caused a ‘loud noise’. Another traveler told the DansDeals website that passengers seated in the row ‘ran away’ and others on the flight started ‘crying hysterically’.

Southwest issued a statement, but didn’t explain how the window broke. No one was injured.

‘The nation’s fourth-largest airline has seen ticket sales slow since the April 17 engine failure. Southwest estimates the drop in sales will cost it between $50 million and $100 million.

‘The Crew of Southwest Flight 957, with scheduled service from Chicago Midway International Airport to Newark Liberty International Airport, made an unscheduled stop at Cleveland-Hopkins International Airport for maintenance review of a potential crack to the outer pane of a window.

‘There are multiple layers of panes in each aircraft window. No emergency landing was declared. The aircraft maintained pressurization, and the flight landed uneventfully in Cleveland.

‘The aircraft has been taken out of service for maintenance review, and our local Cleveland Employees worked diligently to accomdate the 76 Customers on a newq aircraft to Newark. The safety of our Customers and Employees is our number one focus each and every day,’ the statement reads.

Because the cabin never lost pressure, oxygen masks never fell down.

Passengers are seen disembarking the plane after it made an emergency landing in Cleveland

According to FlightAware.com, the plane was traveling 514 mph, 26,000 feet above Lake Erie when it turned around and landed in Cleveland.

PLANE SAILING: THE ROLE OF THE WINDOW HOLE

The air at sea level is said to be around 14.7 pounds per square inch (PSI).

By comparison, a typical flight cruises at between 30,000ft and 40,000 feet and at this altitude the pressure is approximately 4.3 PSI.

Due to a lack of oxygen at this altitude, the plane has to be pressurised in such a way that makes it comfortable and safe for passengers.

Windows on commercial planes typically have three panes – outer, middle and inner – made of acrylic and glass.

The plastic pane on the inside of the plane is to prevent passengers from getting access to the glass panes in the middle and on the outside.

There is a middle pane of glass with a hole in it, then an air gap, followed by an outside pane of glass.

To maintain cabin conditions, it is necessary to manage the pressure between the inner pane and the actual window, so the outer window bears the load of the pressure differential.

If the pane was sealed, and didn’t have a hole in it, all the pressure in the cabin would act on the inside pane of glass.

If this pressure blows that outer plane out, the inside pane is still strong enough to hold pressure and gives pilots time to drop to lower altitudes.

One of the 76 passengers on board, Alejandro Anguina, tweeted that the broken window was on the outside pane.

‘On my way to NJ for work and #Southwest957 gets a window crack. Only outside crack so we’re all safe,’ he tweeted. ‘On our way to NJ in new plane. Thanks to the @SouthwestAir crew and pilots for handling it professionally.’

Another passenger posted a video to Twitter showing a member of the flight crew directing them off the plane after they landed in Cleveland.

‘We’re going to walk you right onto the plane next door and we’re going to let you taken care of,’ the flight crew member says in the video.

Wednesday’s incident comes a little more than two weeks after mother-of-two Jennifer Riordan died on a Southwest flight from New York City to Dallas.

A preliminary investigation indicated that the engine’s fan blade succumbed to metal fatigue – breaking and causing the engine to explode which threw shrapnel and shattered Riordan’s window.

The Federal Aviation Administration ordered inspections of all of the same engines in use by American airlines – about 352 engines in the U.S.

Southwest went beyond the directive and said it was voluntarily testing all engines provided by the same French company, CFM International, that produced the engine in the fatal incident.

The plane involved in Wednesday’s incident was the same type of plane, a 737-700.

The FAA said it is investigating the incident.

‘Southwest Airlines Flight 957, a Boeing 737 flying from Chicago Midway Airport to Newark Airport, requested to divert to Cleveland Hopkins Airport due to a broken passenger window,’ spokesman Tony Molinaro said. ‘The aircraft landed without incident at Cleveland.’

Jennifer Riordan, who was killed on a Southwest flight two weeks ago
She was partially sucked out of this window on the flight from New York to Dallas

Wednesday’s incident comes a little more than two weeks after Jennifer Riordan, left, was killed after being partially sucked out of a window on her Southwest flight from New York to Dallas

The April 17 incident has been blamed on a faulty fan blade. After the incident, Southwest pledged to evaluate all of the engines provided to them by the same French company that manufactured the faulty blade. Above, the engine that exploded last month 

2 thoughts on “Another emergency landing: How a tiny little hole in Southwest window prevented disaster: Failsafe kicked in when outer window pane shattered on board 737-700 at 26,000 feet

  1. Where is the little hole? First, the article says “In fact, it’s that little hole at the bottom of the outside pane that regulates…”, the is states,”There is a middle pane of glass with a hole in it, “.
    WHER IS THE HOLE?

    1. The hole is at the bottom of the middle pane. The outer pane is not glass as the article states but stretched acrylic which makes it stronger. The middle pane is is just a flat thinner piece of acrylic as a dsfety pane with the hole as stated which allows the outer pane to take the pressurization load. The inner pane is only for protecting the middle pane from being scratched, good for viewing through and can be cleaned or easily replaced where the middle and outer pane cannot as they are in a sealed assembly together.

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