Normal gear retraction and lowering is on the centre hyd system. The ALTN system unlocks the main gear doors and nose wheel uplocks using an electric motor. Isaac Newton should then take control. If this motor were to fail (or its respective CB pop) after a centre hyd failure, then a "no gear" scenario could exist.
Unlikely, but entirely possible.
Last edited by 763 jock; 1st Nov 2011 at 16:20.