MD-11 tail fuel management disabled and gross weight.

[DAL2728]

When tail fuel management is disabled, it's my understanding that the max gross weight of the MD-11 becomes 628,000lbs.

When tail fuel management is disabled, does this mean that no fuel is used in the horizontal trim tank? What is used then to keep the aircraft at optimum CG?


I think the majority of KLM's MD-11 fleet is of the 628,000lbs MGW variety. Can anyone confirm this, or explain more about tail fuel management in general?

Thanks!

[vapilot2004]

The FSC (Fuel System Controller) manages the aircraft CG by transferring fuel to/from the tail tank to within 0pct aft and +1pct forward of the desired aft limit during the cruise. The CG functions of the FSC commence after takeoff during climb. The CG is computed on the ground after all passengers/fuel/cargo are loaded and with engines off and no tug attached.

A minimum initial total fuel quantity of 27000kg is required. Rather than using pump output pressure differences to control fuel balance, the FSC has automatic pumps and fill valves connected via manifolds to transfer fuel among the tanks. Fuel tempurature and moisfure protection is managed by transferring fuel in and out of tanks on a timed schedule or according to temps. The tail tank capacity is about 6000kg.

The normal fuel use is scheduled as follows:

FWD Aux (optional)
Lower Aux
Upper Aux
Tank 2 > 1 or 3
Tank 1,2,3 equal burn

Tail fuel is transferred forward when any main tank falls below 5200kg.
During descent below FL200 (or FL260 depending on FSC revision) the
tail fuel will automatically transfer forward to the scheduled tank.

An INOP tail fuel management system can increase fuel burn up to nearly 3% depending on MAC.

[DAL2728]

Thank you very much for this explanation.


Can anyone tell me a little more about KLM's MD-11s and their configuration?