delta flight plunges edited thumb
Panic ensues when plane unexpectedly plunges mid-flight
00:51 - Source: HLN

Editor’s Note: Les Abend recently retired after 34 years as a Boeing 777 captain for American Airlines. He is a CNN aviation analyst and senior contributor to Flying magazine. The opinions expressed in this commentary are his. View more opinion articles on CNN.

CNN  — 

The reports of a Delta Airlines flight on Wednesday, September 18th, en route from Atlanta to Fort Lauderdale, plunging 30,000 feet, describe a dramatic experience—but they appear to mischaracterize something: the incident reflects the execution of a very precise procedure, not a tumble, potentially, into oblivion.

Les Abend

Although the exact circumstances leading to the event have not yet been fully reported, the situation appears to have actually been a very controlled descent.

Small comfort, you say? Why would pilots perform such a descent?

The most likely reason the pilots took this action was a pressurization problem. The pressurization system on an airplane compresses the density of the air volume so that we—you the passengers, and we, the flight crew– can breathe normally at high altitudes where the air is less dense. The system can fail if a leak occurs in the cabin, i.e. a window breaks, or the outflow valve that allows air to escape slowly for circulation has a malfunction, or a pressurization bleed hose comes loose or develops a leak. These are extremely rare occurrences.

Pilots place pressurization problems in two categories: Rapid or explosive. A rapid depressurization is a situation where the cabin pressure is decreasing at a much quicker rate than normal. At some point in time the system will not be able to maintain a breathable cabin pressure. An explosive depressurization, on the other hand, is an event whereupon the cabin loses pressure almost instantly.

Admittedly, both sound not great. But for either event, pilots are trained to perform very specific emergency procedures. The goal is to get the airplane to a breathable altitude, usually 10,000 feet. The first step is for the crew to don oxygen masks. The length of useful consciousness at high altitudes can be as little as 15 seconds. The second step of the procedure is to establish intercom communications between the two pilots through the mic systems in their masks so they can complete their checklists and literally be on the same page.

The third step in the procedure is to ensure passenger oxygen masks have either been deployed in the cabin automatically or deployed manually through a switch in the cockpit. The final step in the procedure is to initiate an emergency descent.

The emergency descent is a very controlled maneuver. The pitch of the airplane is pointed down at an angle that produces a very steep rate of descent. Most passenger oxygen systems, (the dangling masks that everybody ignores during the flight attendant briefing), have approximately 12 minutes of available use, so the objective is to beat the clock. The pilots have a separate system, with almost 60 minutes of oxygen available, depending upon altitude and breathing rate.

Devices on the wing called “speed brakes,” which rapidly destroy lift, are deployed by the pilots to aid in the descent rate. Speed brakes are part of normal operations but are used to their maximum effectiveness during an emergency descent.

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    Although the circumstance and maneuver may seem hair-raising from a passenger standpoint, rest assured that pilots are well-rehearsed. If you find yourself in this very untypical situation, the best contributions you can make are to, first, place the mask over both your nose and mouth. Breathe. Don’t panic. Help someone else. And finally, trust that the pilots are looking out after your best interests.

    Kudos to the entire Delta crew for following their training, and to the professional flight attendants as well.