Copa Airlines flight 135, a Boeing 737-800, veered off the left side of runway 03R while landing at Panama City-Tocumen International Airport. Before starting the approach the crew carried out a Forward threat briefing, highlighting that the reverser of engine no.2 was inoperative per MEL. In case the runway was wet and in case of an asymmetry they would not use the engine no.1 reverse. At the moment of touchdown the crew felt a vibration as if a wheel was deflated, with a strong yaw to the left. They proceeded to apply full rudder to the right to direct the aircraft towards the runway centreline and activated the reverse of engine no.1 to slow the aircraft without success. Perceiving that the yaw moment was increasing and following the procedures, the pilot kept the reverse and continued applying full deflection on the right pedal to return the aircraft to the runway centreline without success. The aircraft went off the side of the runway and stopped. The crew analyzed the situation perceiving a strong smell of burning. The nose gear was collapsed and to avoid possible further damage they decided to shut down the engines, and verified that there was no indication of OVERHEAT or FIRE, proceeded to start the APU to have an alternate power source. An evacuation was carried out without incidents or reports of any person with any injury. Probable Cause(s) Throughout the investigation, it was determined that the accident was a result of the following probable causes: – The weather conditions at Tocumen International Airport at the time of the accident, during the approach to runway 03R, included a night with significant cloud cover, winds at 110 degrees at 11KT, visibility at 6000 in thunderstorms with rain, scattered clouds at 700 feet, scattered cumulonimbus at 1600 feet, overcast at 8000 feet, a temperature of 25øC, and pressure at 1090 hPa. – Operational failure in handling the emergency that occurred, as the landing was recorded with engine power above idle on both engines. The reverse thrust on engine 1 was immediately engaged and accelerated to a value of 84% N1, while N2 on the same engine remained at 41%. The speed brakes and the automatic brake system did not activate. – The surface of runway 03R does not meet the load-bearing capacity required for aircraft that, for any reason, experience runway excursions during landing or takeoff. See appendix 4. Contributing Factors – The weather conditions at Tocumen International Airport, with light to moderate rain over the first 2000 feet of runway 03R. – Loss of control of the aircraft after landing, leading to a runway excursion due to: — Shifts in wind direction during the final seconds before landing. — Light to moderate rain over the first 2,000 feet of runway 03R. — Loss of situational awareness. — Incorrect perception by the pilots, who believed they had gone off the runway due to a flat tire. — Lack of specific training for landing with inoperative reverse thrust and under marginal conditions. — The First Officer?s call of ?Speed Brake Up? and incorrect verification of the brake lever movement. — Failure to manually activate the speed brakes and brakes. — The reverse thrust on engine N1 was not disengaged and was maintained at maximum power after the aircraft began to veer left of the runway centerline.