A rotary wing aircraft (1) provided with an emergency undercarriage (10) for mitigating a failure of a basic undercarriage (2) of the rotary wing aircraft (1). Said emergency undercarriage comprises a main member (20) that extends from a first end (21) to a second end (22), said emergency undercarriage (10) having deployment means (30) for deploying the main member (20) out from a housing (3) in order to take over from a basic undercarriage (2) of a rotary wing aircraft (1) in the event of a failure, said emergency undercarriage (10) being provided with holder means (40) for holding it in position to block said main member (20) when said main member (20) is deployed out from said housing (3).