Are mechanical defects considered fortuitous events?

No. Mechanical defects in the carrier are not considered a caso fortuito that exempts the carrier from responsibility. (Sweet Lines, Inc. v. CA, G.R. No. L-46340, Apr. 29, 1983)

1. Tire blowout of a jeep is not a fortuitous event where there exists a specific act of negligence by the carrier consisting of the fact that the jeepney was overloaded and speeding at the time of the incident. (Juntilla v. Fontanar, G.R. No. L-45637, May 31, 1985)

2. Defective brakes cannot be considered fortuitous in character. (Vergara v. CA, G.R. No. 77679, Sept. 30, 1987)