Airbus Laws
 

I am very familiar with the Airbus flight laws but one thing puzzles me.

I understand that when the gear is down you will be in Direct Law. Does that mean on approach you have no stall or energy protections?

Direct law is exactly that.. Direct. No protections.

Could someone please explain..

Airbus Laws? First law is that at least once in your Airbus flying career the aircraft will scare you witless by doing something that Airbus themselves will say, initially anyway, is impossible!

Sorry ..... couldn't help myself ..... I hope you get the real answers you're after. :ok:

You may want to look in here: http://www.pprune.org/forums/showthread.php?t=245735

not so fammiliar with airbus laws I can see! you will normally not be in direct law when gear selected down, unless you have some system failures.

read the books I would like to suggest!
regards,
nikky

Airbus Laws
 

With regard to the A330.

NORMAL LAW

Consists of three modes - in order of occurrence GND/FLT/FLARE and GND again at landing. Transition between each is conditional on factors like pitch attitude, RA, time and whether the aircraft is on the ground or in flight. The position of the landing gear has no effect on normal law control and complete flight envelope protection is provided in FLT mode.

ALTERNATE LAW

There are numerous combinations of failures which will result in a reconfiguration into ALT LAW. There are two types both of which are characterised by pitch control which is very similar to normal law pitch control. In both types of ALT LAW the protections are almost totally lost except for load factor protection. Availability of high and low speed stabilities is conditional as well. Audio stall warning is activated in both types at a safe margin from actual stall. Gear extension may require some forethought as in some cases (e.g. EMER ELEC CONFIG) the autotrim is lost.

DIRECT LAW

This condition is arrived at as a result of failures like triple IR/PRIM. Pitch and roll are in direct law - direct sidestick to surface relationship. There is no autotrim and ALL protections are lost. Again gear extension may require some forward planning.

There is one hybrid type failure which can cause confusion and that is the dual RA fault. RA is one of the primary inputs for normal law control of transition from flight mode to flare mode. Instead of RA information the flight control system uses inputs from the LGCIU to determine mode switching. So when the gear is down in this case a switch to flare mode occurs and autotrim is lost. EGPWS is inoperative and the low energy warning is lost as well.

Long-winded I know but hope it helps.

Have to backup Nick ......... and even more so Mr Bernoulli ........

Normal Law = Ground mode, Flight mode, Flare mode, you will be in normal law all the way, when everything is normal.

If more than one failure has caused degradation to Alternate law, you will go into Direct law once you lower the gear.

mourgo,
When the a/c is in normal law the flt ctrl system is able to blend flare mode;attitude;nose down pitch order etc to achieve a safe landing.
However with system degraded to, say alt law the same is not possible. hence in order to provide you full authority of flight ctrls the system reverts to direct law on selecting gear down. stall warning is always available as in all aircrafts. energy protection is taken care of by the auto thrust/g/s mini function:)