Alaska Airlines Flight 261 - Conclusions

Conclusions

In addition to the probable cause, the NTSB found the following contributing factors:

• Alaska Airlines' extension of its lubrication interval for its McDonnell Douglas MD-80 horizontal stabilizer components, and the FAA's approval of that extension, the last of which was based on Boeing's extension of the recommended lubrication interval increased the likelihood that a missed or inadequate lubrication would result in excessive wear of jackscrew assembly acme nut threads and, therefore, was a direct cause of the excessive wear and contributed to the Alaska Airlines flight 261 accident.
• Alaska Airlines's extended end play check interval and the FAA's approval of that extension, which allowed the excessive wear of the acme nut threads to progress to failure without the opportunity for detection
• The absence on the McDonnell Douglas MD-80 of a fail-safe mechanism to prevent the catastrophic effects of total acme nut loss

During the course of the investigation, and later in its final report, the NTSB issued a total of 24 safety recommendations, covering maintenance, regulatory oversight, and aircraft design issues. More than half of these were directly related to jackscrew lubrication and end play measurement. Also included was a recommendation that pilots were to be instructed that in the event of a flight control system malfunction they should not attempt corrective procedures beyond those specified in the checklist procedures, and in particular in the event of a horizontal stabilizer trim control system malfunction the primary and alternate trim motors should not be activated, and if unable to correct the problem through the checklists they should land at the nearest suitable airport.

In NTSB board member John J. Goglia's statement for the final report, which was concurred with by all three other board members, he wrote:

"This is a maintenance accident. Alaska Airlines' maintenance and inspection of its horizontal stabilizer activation system was poorly conceived and woefully executed. The failure was compounded by poor oversight...Had any of the managers, mechanics, inspectors, supervisors or FAA overseers whose job it was to protect this mechanism done their job conscientiously, this accident cannot happen...NTSB has made several specific maintenance recommendations, some already accomplished, that will, if followed, prevent the recurrence of this particular accident. But maintenance, poorly done, will find a way to bite somewhere else."