Denti
Boeing FBW and AB FBW are based on different philosophies. AB is maximum automation with auto trim and alternate law in degraded mode. In case of double failure of ADRs or IRs when computers cannot self detect the job is given to the pilot, the direct law comes in as a short term phase and alternate law is recovered after pilot identifies and switches off the faulty component. The other case is in A320 where direct law comes in as a flare mode of alternate law after gear is down to help you land. Since there is no Q or any tactile feed back in the stick as is the case in conventional aircraft or Boeing FBW the direct law handling is different than in normal and alternate law. So there is a an interim procedure to enable you override protections, giving a switch to induce direct law in complicated situation for long term may not be a good idea and nor is it required if pilots follow correct procedures. Auto trim in alternate law driving the stab to its limit has happened as a result of mishandling and was pilot induced. Airbus philosophy has its own followers and is quite popular amongst them.
Last edited by vilas; 12th Jan 2015 at 08:36.