SEATAC, Wash. -
Boeing is hunting for the cause of a troubling engine problem on dozens of 737 flights, and contaminated fuel may be the culprit.
Investigators said they are examining fuel at Sea-Tac Airport but are also looking at other west coast airports and at the machinery on the plane.
The uncommanded engine oscillation, as Boeing calls it, has happened on 32 flights over five years. More than half the incidents happened on 737s flown by Seattle-based Alaska Airlines.
It is usually brief -- 10 seconds or so – but worrisome enough that about half the flights returned to their bases.
There have been no incidents since a software upgrade in December to the planes' computerized throttles.
It's only happened on what's called the next generation 737 which is the current model.
They have flown 23 million flights since the first of these incidents in 2008, so it is a rare problem.
In the last 10 years, Sea-Tac built underground tanks and pipes to deliver fuel straight to the gates, but a company called Swissport is contracted to run the system.
Most fuel is put into the planes by another company, ASIG.
A spokesman for the airport said he wasn't aware of the 737 problem, as the airport doesn't deal directly with the fuel.
Even if it is primarily a contaminated fuel issue, it is complicated. There may not be a direct line between the oil in the ground and the problem on the planes.
Another complicating factor is that planes fill up in a number of places, dictated by who has the least expensive gas, or if the airline has a long-term contract with a company to keep the cost down.
Because fuel is one of an airline's biggest expenses, airline officials watch prices closely.