Originally Posted by
Starbear
In short, yes it is. To use ALTN Gear extension, the Landing Gear Lever should be in the OFF postion (hydraulics in a "runaround" type circuit) so if there is any hydraulic pressure available, gravity extension will merely push the fluid around the circuit. If the lever is left in the UP postion then its possible for fluid/pressure to be trapped in up circuit and so resist gravity extension.
But question is whether committing such an error once could possibly lead to no further possibility to extend the gear in any manner. That would be too simple explanation if systems allowed for such a simple pilot error, so I suppose that reconfiguring the gear lever and switching the ALTN to DOWN again would release the pressure and allow for gravity extension, despite not having center hydraulic system available.
The latest news (released by press/airport authorities, not the airline, so please consider some bias on accuracy) on the technical part of this topic is that the gear has been extended from the inside of the aircraft (I assume it means cockpit) by the engineers sent by Boeing. So could it have been possible after all?...