Air France rushed on Tuesday to replace speed monitors suspected of feeding false information to the computers of Flight 447 and leading to a series of failures that broke the plane apart over the Atlantic Ocean. Four more bodies were pulled from the sea, and helicopters began ferrying other remains to shore.

A total of 28 bodies have been recovered; 200 others have yet to be found.

With the plane’s data recorders still apparently deep in the ocean, investigators have been focusing on the possibility that external speed monitors — called Pitot tubes — iced over and gave dangerously false readings to the plane’s computers in a thunderstorm. The L-shaped metal Pitot tubes jut from the wing or fuselage of a plane, and are heated to prevent icing. The pressure of air entering the tubes lets sensors measure the speed and angle of flight. A malfunctioning Pitot tube could mislead computers controlling the plane to dangerously accelerate or decelerate.