DALLAS (AP) - American Airlines says improperly installed clamps caused seats to come loose on some planes, and it's expanding an inspection to cover dozens of jets.

In the past week, rows of seats have come loose on three separate flights, two of which made emergency landings.

American said Tuesday the problem was caused by improper installation of a clamp used to attach each row of three seats to tracks on the aircraft floor.

The airline had planned to inspect eight of its Boeing 757 jets, but says instead it already inspected 36 and plans to check 11 more. All have the same model of seats in the main cabin.