Boeing Co. has issued a safety bulletin reminding pilots of the steps required to ensure they maintain control of their aircraft in the wake of last month’s deadly plunge of an Indonesian jetliner into the Java Sea.
The Flight Operations Technical Bulletin, dated Monday, was sent to Boeing customers around the world. Its purpose is to “reinforce active flight crew monitoring of airplane state and flight path management to prevent airplane upsets.”
While it doesn’t specifically address Sriwijaya Air Flight SJ182—which went into an abrupt dive shortly after takeoff on Jan. 9, killing all 62 aboard—it is a high-level reminder for pilots to monitor their aircraft for the kind of issues that occurred prior to the crash and how to recover from such situations.
“Loss of Control In-flight remains the single greatest cause of fatalities in commercial aviation,” the company said in the document reviewed by Bloomberg News. “This bulletin is meant to reinforce the importance for active monitoring of the airplane state while managing the airplane flight path.”
Less than three minutes after departing from Jakarta, the left engine on the 737-500 began reducing power as the right engine’s setting remained the same, according to a preliminary report issued Feb. 10 by Indonesia’s National Transportation Safety Committee.
Such unequal thrust settings can cause a plane to turn if they aren’t countered properly. According to the report, there were indications the pilots weren’t able to maintain their assigned heading. At the same time, the flight crew was attempting to turn around a storm, so might also have been distracted.
About 83 seconds after the throttle issue arose, the plane banked more than 45 degrees to the left and within seconds it was diving toward the Java Sea from a height of almost 11,000 feet (3,354 meters).
Indonesian investigators haven’t said what caused the crash, but it’s clear that the plane went out of control in the final 30 seconds of the flight.
“Boeing regularly communicates with customers on how they can safely and confidently operate their airplanes,” the company said in an emailed statement. “In close coordination with investigative and regulatory authorities, these latest communications reinforce the importance of industrywide and Boeing guidance and training materials on aircraft upset prevention and recovery.”
In the bulletin, the company lists various causes that can trigger a loss of control, which include malfunctions and incorrect actions by pilots. Preventing such concurrences “involves the active participation of both pilots,” it said.
“Active monitoring skills are essential to facilitate early detection of conditions that can lead to an airplane upset,” the company said. An upset occurs when a plane flies too slowly or banks, climbs or descends too steeply.
It also warned against distractions and complacency. “Highly automated and reliable flight control systems have greatly reduced pilot workloads, but the requirement for monitoring complex systems has increased,” it said.
As in the Sriwijaya Air accident, which began with what appears to have been a relatively minor issue with the jet’s automatic throttle control, Boeing said pilots need to keep a close watch for signs of unusual flight activity.
“Minor excursions such as simply overbanking in a turn or flying slow on approach can progress to a larger divergence from the intended flight path and lead to an airplane upset condition and potential loss of control,” the company warned.