744 NAI
Another question to which I fail to find a satisfying answer. Any thoughts would be greatly appreciated.
The 744 MEL allows you to dispatch with the NAI valve secured OPEN, provided the HP valve is secured closed. By keeping the bleed valve OFF for the entire flight (except during start), this procedure essentially has you using the Firewall Valve as your NAI valve by use of the NAI switches. (Selecting NAI ON with the Bleed valve OFF will automatically open the Firewall Valve, and since the NAI valve is already secured OPEN, provide IP bleed air to the Engine Nacelles. )
Now.. for the question;
The manual requires a enroute climb-penalty of almost 8 tonnes to be applied. Anyone care to guess why?