What happened: Lando lost rear braking stability and fought oversteer entering the Turn 15 left-hander at Circuit of the Americas during Friday practice. The slide interrupted soft-tyre qualifying simulations on the opening day of the United States Grand Prix weekend.

Why it matters: Rear-axle instability in Austin's slow-speed final sector tests a McLaren team working to close a three-month development deficit as its new aerodynamic package hits the track after 17 rounds. Dialing in braking balance with the revised floor is essential before cars enter parc ferme conditions.

What to watch: McLaren engineers will analyze Friday telemetry overnight to adjust rear-end setup ahead of Saturday's qualifying sessions at Circuit of the Americas.