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Alaska Airlines Inspects Fleet After Unscheduled Landings

by Jack Penning

Posted on February 24, 2006 at 6:24 PM

Updated Wednesday, Nov 4 at 2:46 PM

Northwest NewsChannel 8 first reported that an Alaska Airlines jet was forced to make an unscheduled landing in Portland when oxygen masks deployed shortly atfer takeoff. It happened on Tuesday, February 21st. Now we know it's one series of incidents for Alaska.

Since December 26th, Alaska jets have made at least six unscheduled landings due to pressurization problems... and five in the last 10-days. Pilots have been forced to make those landings everywhere from Washington, DC to Anchorage.

What exactly is a "pressurization problem?"

To answer, we have to explain the reason behind "pressurizing" a plane. Jets fly high in the atmosphere... typically between 26,000 and 41,000 feet... where the air is very thin. In order for passengers to breathe, extra oxygen has to be pumped into the cabin. If that extra oxygen wasn't added, we'd pass out in seconds. When the extra oxygen is pumped in, it's joined by other atmospheric gases. That gives in interior of the plane the "pressure"... or air density... you'd normally experience at 10,000 feet. Thus, the pressure is much higher inside the plane than it is outside.

When a plane can't "hold" pressure... air leaks out... into the atmosphere. If it leaks enough air, and interior pressure continues to fall, the cabin loses the necessary oxygen for passengers and crew to breathe normally. That's typically when oxygen masks deploy. With masks, passengers can keep breathing... and stay alert... until the pilot can descend to the point where breathing is easier (usually around 10,000 feet). At that point, the captain will normally initiate an unscheduled landing... but usually won't declare an emergency, unless there are injuries.

Injuries are usually minor, and typically include ear and sinus pain, caused by the rapid change in air pressure on the ear canals and nasal passages.

Pressurization problems aren't particularily dangerous, or uncommon. NTSB Investigator Jim Struhsaker told The Seattle-Times, "Every morning, we get a list four pages long of these types of incidents."

What is uncommon, is for one airline to have so many seemingly similar incidents in such a short period of time. Although Alaska Airlines spokesperson Amanda Tobin told the Seattle-Times, "our initial investigations of each incident has found different root causes for each one, which would not indicate a systemic issue."

Still, it's serious enough that Alaska is doing a fleet-wide sweep. The airline will thoroughly inspect the pressuization system on each of its 110 737s and MD80s... to make sure there isn't some underlying problem.

The Incidents Explained

- December 26, Alaska Airlines Flight 536: En route to Burbank, from Seattle, flight 536 made an emergency landing back at SeaTac due to a loss of cabin pressure. When the plane landed, crews found a foot-long hole in the side of the fuselage. An Alaska investigation showed a ground worker hit the plane with a baggage cart, but didn't alert the crew. Aircraft: MD-83.

- February 14, Alaska Airlines Flight 578: This flight returned to SeaTac, shortly after takeoff for Denver with a pressurization problem. Five passengers were treated for ear and sinus problems. The airlines says an electrical malfunction caused the cabin to lose pressure. Aircraft: B737-400.

- February 18, Alaska Airlines Flight 1: Flight 1 took off from Washington's Reagan National Airport, bound for Seattle, when the captain realized the plan wouldn't pressurize. He diverted to Dulles Airport, in northern Virginia. Ground crews quickly found that a door hadn't been properly closed. Aircraft: B737-700.

- February 21, Alaska Airlines Flight 100: Flight 100 took off from PDX bound for Denver, but never made it past Mt. Hood. Shortly after takeoff, oxygen masks deployed. The captain returned to Portland... where crews have been looking for the cause of the incident. Alaska says it's possible the aircraft depressurized in flight. Aircraft: B737-400.

- February 22, Alaska Airlines Flight 397: This flight took off from Ontario International Airport in California, bound for Seattle. Shortly after takeoff, the captain noticed the plane was pressurizing more slowly than normal. He elected to divert to LAX, where he made an uneventful landing. Aircraft: MD-83.

- February 23, Alaska Airlines Flight 65: En route from Juneau to Anchorage, an alert sounded, indicating there wasn't sufficient cabin pressure for the aircraft to fly at it's assigned altitide. The pilot descended to 10,000 feet, and continued to Anchorage, where the plane landed safely. One passenger was treated for ear pain. Alaska is still pinpointing the cause of the alarm. Aircraft: B737-400.

Appendix: Alaska Airlines

Alaska Airlines, together with partner Horizon Air, is Portland's largest carrier. Together, Alaska and Horizon operate more than 200 daily flights at PDX. Portland serves as the airline's second-largest hub, after Seattle.

Alaska 737-800.jpg
Alaska Airlines Boeing 737-800 (courtesy Alaska Airlines).

Alaska operates four versions of the Boeing 737... including the older 737-400... and the newer 737-700, 737-800, and 737-900. There are 78 737s in the Alaska fleet, with more than 30 still on order.

Alaska MD-80.jpg
Alaska Airlines Boeing MD-80 (courtesy Alaska Airlines).

Alaska also operates the Boeing (former McDonnel Douglas) MD-80. There are 26 MD-80s in the Alaska fleet.