Federal regulators are extending the grounding of some Boeing jets after an Alaska Airlines plane lost a side panel last week. The Federal Aviation Administration said Tuesday that guidelines for inspecting the planes for safety are being revised. That's causing more flight cancellations for Alaska and United Airlines, which can't use their Boeing 737 Max 9 jets. A panel called a door plug blew off an Alaska jetliner over Oregon last week. The investigation is putting pressure on plane maker Boeing and its key supplier, Spirit AeroSystems.