A nacelle may include a pylon and a thrust reverser having an inner fixed structure. A locking mechanism may automatically engage and prevent relative movement between thrust reverser halves. A bumper may be coupled to the inner fixed structure. The locking mechanism may limit deflections between the thrust reverser and the pylon in response to a burst duct. A locking mechanism in the inner fixed structure may include a pressure relief door and an arrestor which hooks onto a retaining bar in a pylon bracket. The locking mechanism may allow the thrust reverser halves to be opened for access to the engine.