Boeing’s 767-based tankers use a version of the pitch augmentation system that grounded the 737 Max 8 fleet, the manufacturer and U.S. Air Force officials say.
The disclosure provides a new data point in the unfolding story of how Boeing installed the Maneuvering Characteristics Augmentation System (MCAS) on narrowbody airliner fleet.
Both the KC-767 and KC-46 fleets delivered to air forces in Italy, Japan and the U.S. rely on the MCAS to adjust for pitch trim changes during refueling operations.
In the 1980s, Boeing’s engineers considered using a pitch augmentation system for the commercial version of the 767, but dropped the idea after finding that vortex generators provided adequate control.
By 2011, Boeing had already delivered KC-767s to Italy and Japan fitted with the first version of MCAS. The use of the system then spread as Boeing won the Air Force’s KC-46 contract in February and launched the 737 Max 8 in August.
But Boeing designed the integration on the KC-767 and KC-46 slightly differently than on the 737 Max family.
The single-aisle airliner uses one angle of attack vane — either the captain’s or first officer’s — to generate the data used by the flight computer to activate the MCAS.
By comparison, the KC-767 and KC-46 are designed to use two sensor inputs to feed angle of attack data, Boeing says.
Boeing spokesmen declined to elaborate on which sensor inputs are used to provide the data in the tanker design. The options include using data from the angle of attack vanes on both sides of the cockpit, or an angle of attack vane an inertial gyroscope.
How the MCAS functions has come under the microscope since the March 10 crash of a 737-8 on Ethiopian flight 302. It was preceded by a Lion Air 737-8 crash in October after an abrupt dive. Preliminary findings released by Indonesian investigators linked the Lion Air crash to erroneous data provided by angle of attack sensors. A Ethiopian airline official said preliminary information about Ethiopian crash revealed similar control problems.
The U.S. Air Force has launched a review of flight procedures for the KC-46, a spokeswoman says.
“The USAF does not fly the models of aircraft involved in the recent accidents, but we are taking this opportunity to exercise due diligence by reviewing our procedures and training as part of our normal and ongoing review process,” she says.