Many airlines lubricated jackscrews more often than Alaska

Alaska Airlines' lubrication schedule for the jackscrew of the horizontal stabilizer on MD-80 jetliners - the part that is the focus of the Flight 261 crash investigation - was much less frequent than the schedule of many other airlines.

At the time of the Jan. 31 crash, Alaska lubricated the jackscrew every 2,500 flight hours, or about every eight months. Other carriers lubricate it as frequently as every 500 flight hours - five times as often.

Investigators don't know if lack of lubrication was an issue in the crash of the Alaska MD-83, but it is under consideration at the National Transportation Safety Board's laboratory in Washington, D.C.

Investigators will find a wide range of lubrication intervals for similar-type planes - in this case, closely related DC-9s, MD-80s, MD-90s and 717s, which were designed by McDonnell Douglas but now are considered Boeing products.

A Seattle Times survey of airlines flying those planes found that the schedule for greasing or checking the lubrication of the jackscrew assembly ranges from 500 flight hours in the case of Airborne Express to 2,500 flight hours for Alaska and US Airways.

In between, Stockholm-based SAS checks the jackscrew every 600 flight hours and lubricates it as needed. American Airlines lubricates every 900 flight hours, Hawaiian Airlines every 1,000.

All of those maintenance regimes were blessed by the Federal Aviation Administration. Maintenance schedules are approved case by case, based on an airline's experience, the age and history of its fleet and the environment in which it flies.

The sequence of events leading to the Flight 261 crash began with the apparent malfunction of the jackscrew assembly. The jackscrew tilts the stabilizer to adjust the plane's angle of flight in various situations. On Flight 261, the stabilizer had jammed in a position that made the plane's nose tend to drop.

The pilots struggled with this control problem for at least half an hour before the plane crashed into the Pacific Ocean near Oxnard, Calif., on Jan. 31, killing all 88 people aboard.

In the submerged wreckage, the stripped threads of what is known as the gimbal nut, which is made of a metal alloy, were found wrapped around the harder steel jackscrew. The gimbal nut was found fully detached.

Investigators don't know if lack of lubrication, the presence of a foreign object or a manufacturing defect could have caused the stripping.

After an urgent airworthiness directive last weekend, which called for inspections of jackscrews on more than 1,100 U.S.-registered planes, all carriers flying planes like the MD-80 must inspect and, if needed, lubricate jackscrews every 650 flight hours.

Results of those inspections found 22 planes nationwide with reportable problems, ranging from grit in the grease on the jackscrew to failure of a test that measures gimbal-nut wear and determines whether the jackscrew assembly should be replaced.

At least in the context of those results, longer lubrication intervals don't necessarily relate to increased wear.

With its 2,500-hour lubrication interval, Alaska had the most planes with reportable problems - six. Five of them failed the gimbal-nut wear test. That's disproportionate representation given the airline's fleet of 34 MD-80s.

But US Airways, with the same lubrication interval of 2,500 flight hours and a much larger fleet, had no reportable problems among its 62 planes of that type.

At the other end of the scale, Airborne Express, with the most-frequent lubrication interval of 500 flight hours, had no reportable problems in its fleet of 73 airplanes of that type. Nor did American, with its 900-hour lubrication schedule.

Yet Hawaiian, with a relatively frequent 1,000-hour lubrication schedule, had three planes out of 15 turn up on the FAA list of problems.

Other major carriers with problem reports - AirTran Airways (three planes out of 44), Delta Air Lines (five planes out of 136), Northwest Airlines (three planes out of 172) and TWA (one plane out of 131) - either declined to provide information or could not cite a specific lubrication interval in terms of hours.

Some of the jackscrews from the inspections have been sent to the NTSB, which is comparing the types of grease and the makeup of the gimbal nut's metal to see if there are differences.

Lubrication intervals vary so much from airline to airline because of the way the FAA oversees air carriers. The agency assigns inspectors to each airline. Their primary purpose is to ensure that their carrier adheres to the procedures, such as maintenance schedules, that the inspectors have approved.

"They don't regulate, they oversee," said Michael Barr, the director of aviation-safety programs at the University of Southern California. "There's a big difference. It would be impossible for them to regulate it by observation. They just don't have the manpower."

Doug Hurlihy, an aviation-safety consultant and former NTSB accident investigator, said the inspectors watching over airlines develop close relationships with the carriers and "are allowed a considerable latitude of discretionary power" by FAA headquarters in Washington, D.C.

That's one reason policies and standards vary from carrier to carrier. But the process involved in determining a minimum maintenance program contributes to the differences, too.

It starts with a manufacturer's recommended beginning maintenance schedule for an airplane type, which is determined with FAA involvement. Early in a model's history, the maintenance schedule is conservative. As carriers develop a body of data about how parts wear and what other problems crop up, the manufacturer's recommendations are adjusted.

When a carrier opens for business or introduces a new airplane into the fleet, it uses the manufacturer's recommended maintenance regime as a starting point to create its own program.

A number of factors might call for modifying the recommended maintenance schedule, such as the number of landings and takeoffs the planes make in a day, the climate in which they operate, the maintenance history of the aircraft involved and the experience of the airline's maintenance department.

In any event, the FAA inspectors assigned to the airline sign off on the maintenance program.

Over time, the airline can modify the maintenance schedule with FAA concurrence, usually to lengthen the intervals for inspections, lubrication or overhaul of systems. Larger carriers tend to be more aggressive about this than smaller ones because even minor changes in maintenance intervals can save a great deal of money across a large fleet of planes.

Such changes must be backed by a demonstrated history of reliability, the FAA says. The manufacturer also plays a role, according to Boeing, but only by providing fleetwide data that might help an airline justify the change.

Alaska's longer time between jackscrew lubrications, for example, is the result of "demonstrated reliability," the carrier said in a written statement.

"Essentially, it's whatever the inspector and the airline agree makes sense," Hurlihy said. "It's a very gray area. There is nothing black and white."

Said Barr, of USC: "In my opinion, there should be the same standard for everything."

The Flight 261 crash is far from being linked to lubrication or any other maintenance issue. The severity of the damage to the jackscrew in the wreckage is unlike anything the FAA inspections found in in-service planes, leaving open the possibility of a manufacturing defect or some other factor.

But Alaska Airlines' prominent showing in the inspection findings, and the fact a grand jury is looking at undisclosed practices at the airline, have heightened interest.

The NTSB says it is continuing to examine the airline's maintenance records. As part of that scrutiny, investigators are looking into maintenance intervals. They might find that the system of customized maintenance programs worked in this case. They also may formally recommend that the FAA try something else.

Seattle Times reporters Byron Acohido and Steve Miletich contributed to this story.

Chuck Taylor's phone-message number is 206-464-2465. His e-mail address is: chucktaylor@seattletimes.com.