Mutt: Required landing charts for dry runways do not include reverse thrust. This is a certification rule. Reverse thrust is only included in contaminated runways. In the Lauda case i think that the problem was not the reverser deploying but the fact that the engine was running at high N1 when the reverser deployed. When manually activating reverse you first go to idle thrust which I donīt beleive would cause a problem in flight. However as the reverser in the Lauda flight extended by itself it did so at a high thrust setting causing interupted airflow over a section of the wing as well as developing a significant yaw.