744 Vmcg increase with HDP inop
Would anyone be so kind and help me properly understand the following 744 issue?
The 744 MEL requires a 5 knot increase to the Vmcg with the No. 1 or No. 4 Hydraulic Demand Pumps inoperative. The scenario implies, of course, that you lose the associated engine on takeoff and thereby experience a complete loss of hydraulic system 1 or 4.
Yes, with the No.1 system inoperative, you lose nose and body-gear steering. But Vmcg certification is predicated on the use of aerodynamic forces alone, so I can't see that being the reason.
Yes, the Lower and Upper rudders are powered by systems 4 and 1 respectively, but with redundancy back-up from systems 2 and 3. So even with a complete loss of Systems 1 and 4, you've still got the full 3000PSI powering the rudder.
That's where the trail goes cold for me.
Any other ideas would be appreciated?