On the 1st of April this year, Southwest Airlines flight 812 departed from Phoenix for Sacramento. There were five crew and 118 passengers on board.

At 34,000 feet, climbing through to FL360, there was a loud sharp noise. The cabin experienced rapid decompression and the oxygen masks deployed.

Shawna Malvini Redden, a passenger on the flight, blogged about the experience:

The Blue Muse: Southwest Flight 812: I prefer my plane without a sunroof, thanks

An explosion. A loud rush of air. A nosedive toward the ground. An oxygen mask? I had not anticipated a change in cabin pressure. With hypoxic fingers, I fumble the mask. With chagrin, I realize it really does not inflate. To my right, a mother shrieks in hysteria, her panic rising above the din. Ahead, a young man with curly brown hair and an easy smile walks about, helping to affix oxygen masks. Behind me, a woman’s tears stream down her face as the shock sets in. I realize I have my seat mate’s hand in a death grip. This is Southwest Flight 812.

The pilot immediately began a descent. The Federal Aviation Commission released the audio recordings this week which you can hear on the FAA site or read online: PDF Transcripts of Southwest Flight 812, April 1, 2011.

Here’s the initial discussion, with added punctuation and the times given as local time. R6 and D31 are controllers covering specific sectors in the Los Angeles Air Route Traffic Control Center.

15:55:57 Southwest Airlines 812 Southwest eight twelve. Thirty two climbin to flight level three six zero. 15:56:00 R60 Southwest eight twelve LA center roger. 15:57:47 Southwest Airlines 812 Center (unintelligible) eight twelve 15:57:51 R60 Southwest uh I’m sorry who was that 15:57:55 Southwest Airlines 812 …twelve 15:57:56 R60 I missed that last call. Who was that? 15:57:57 Southwest Airlines 812 …twelve 15:58:00 R60 Southwest eight twelve uh was that you? 15:58:02 Southwest Airlines 812 Yes sir (unintelligible) declaring an emergency descent declaring an emergency we lost the cabin. 15:58:08 R60 Yeah Southwest eight twelve I’m sorry, I could not understand that. Please say again. 15:58:12 Southwest Airlines 812 Requesting an emergency descent. We’ve lost the cabin. We’re starting down. 15:58:15 R60 Southwest eight twelve descend and maintain flight level two four zero. 15:58:20 Southwest Airlines 812 Two four zero Southwest eight twelve. 15:58:24 R60 What altitude do you need? 15:58:26 Southwest Airlines 812 (unintelligible) We need uh ten thousand. 15:58:29 R60 Understood. 15:58:33 D31 Sector ten and thirty one. 15:58:35 R60 Yeah this is Sector uh sixty. Southwest eight twelve is a emergency decompression descent he’d like ten thousand feet. Can you approve that? 15:58:43 D31 Uh… 15:58:45 R60 He’s doin’ it anyway. 15:58:47 D31 Yes. Yes, approved. 15:58:48 R60 He’s descending to ten thousand (unintelligible) I’ll be flashing him to you. 15:58:52 Unknown You done good.

The flight was approved for a direct return to Phoenix but then they realised that Yuma International Airport, a “shared use” military and commercial airport, was closer. The flight landed at Yuma at 16:32 local time. A flight attendent and one passenger received minor injuries as a result of the incident; both were treated at the airport.

The aircraft had a large tear in the fuselage. The NTSB reported that it was a 5-foot by 1-foot (152cm by 30cm) hole in the crown area on the left side, aft of the over-wing exit.

NTSB Continues Investigation of Southwest Airlines Flight 812

The 59-inch longitudinal fracture occurred in the aluminum fuselage skin along the lap joint at stringer-4 left (S-4L) between body station (BS) 666 and BS 725. At S-4L, the crown skin overlaps the lower skin forming a lap joint. The two skins are connected at the lap joint by three rows of rivets (referred to as lower, middle, and upper row of rivets.) The fracture was through the lower skin and connected 58 consecutive rivet holes in the lower row of lap joint rivets. The exterior surface of the skin in the area of S-4L is painted blue. Evidence of blue paint was also found inside the joint between the upper and lower skin and on several areas of the skin fracture surface.

Southwest grounded 80 aircraft as a result of this incident, all Boeing 737-300s which had not already had the skin on their fuselage replaced. Boeing announced a Service Bulletin instructing operators to inspect the aircraft. This was followed by the FAA issuing an Emergency Airworthiness Directive on the subject.

NTSB Continues Investigation of Southwest Airlines Flight 812

The Federal Aviation Administration issued Emergency Airworthiness Directive AD 2011-08-51 on April 5 mandating the inspections in the Boeing Service Bulletin. To date, the NTSB has been informed that 136 airplanes have been inspected worldwide in accordance with the Service Bulletin and Airworthiness Directive including all U.S. registered airplanes covered by the Directive. As stated in a previous release, four of these airplanes were found to have crack indications at a single rivet and one airplane was found to have crack indications at two rivets. These airplanes had accumulated between 40,000 and 45,000 total cycles. The lap joints from these areas of the subject airplanes have been removed and will be fully documented as part of the NTSB investigation.

The investigation continues but it did make me happy to hear the utter competence with which the flight crew and ATC dealt with the emergency. Hurray for happy endings!