A300-600 rudder vs 767

[mstram]

From the thread "AAL 300 Accident" in Rumours and News:
http://www.pprune.org/forums/showthread.php?s=&threadid=118045

"Ronald Hess, .... is an aeronautical engineering professor at the University of California-Davis.

..

"But after the A300-600's rudder begins to move, it requires far less pressure to swing the rudder an equal distance than on other types of jets.

At 290 mph, a pilot who had begun to move the rudder need only add 10 pounds to the pedal to swing the rudder all the way to one side.

By comparison, the similar-sized Boeing 767 requires 63 pounds of additional pressure to move the rudder as far as possible.


1) Is that true (10 lbs vs 63 lbs) rudder force for full deflection?

2) If it is true, is that a problem ?

3) If it is a problem, then is there a flaw in the certification regulations / process ?

[safetypee]

One possible issue here is the difference between Constant Pedal Force and Pedal Deflection, vs Variable Pedal Force and Pedal Deflection Systems. Boeing (Seattle) aircraft use the first whereas Boeing (Long Beach) uses variable force and deflection (and probably Airbus).

Whilst in the first instance the force and rudder pedal travel remains constant with change of speed, and in the second it does not; the differences are only apparent with increasing airspeed where for both systems the actual rudder surface deflection is limited by the structural loads requirements.

So for 1. the statement “full deflection” is true when describing the rudder pedal movement, but false when describing the rudder surface at 290 kts.

For 2. Not a problem for pure deflection. The issue emerging from the Airbus accident is that the regulations do not deal with dynamic rudder deflections, particularly if the rudder pedal is repeatedly reversed.

3. Quite possibly, but previously the industry and pilots have managed to avoid the problem. Perhaps the Airbus accident is an indication as to the different standard of aircrew behaviors that the industry now has to endure.

Advice on the use of rudder is given by IFALPA here: www.ifalpa.org under Safety & Security Bulletin Archive
Safety Bulletin 03SAB002 Airbus
Safety Bulletin 03SAB001 Boeing

[Shawn Coyle]

It's even more subtle than that.
Evidently (since I haven't done it myself) the breakout force to just start moving the rudder in the A300 is 25 lbs. And the force for maximum deflection is 35 lbs.
Your legs and feet are very poor position sensors, and are not used as such by pilots very much. They are also pretty poor force sensors.
A high breakout and not much more force to get to maximum deflection is a pretty good way to get into a PIO, according to the late Ralph Smith, who was an acknowledged expert on this matter.
I remember clearly the day he came into my office to talk about this very accident and was pretty strong in his opinion that this was traceable to the mechanical characteristics of the system.

[sycamore]

Have to agree with you Shawn,as most fixed wing pilots dont use the pedals that much, a good spring and a rate damper in the system would have been a much better option !!!

I`m sure Wastelands have a few old Wessex and Sea-king ones they could flog to Airbrush....

[safetypee]

Even more subtleties Shawn. The mechanics of the system often leads to problems as you describe, but many authorities ‘request’ very high break out forces to prevent inadvertent rudder input. Commercial crews have to stretch their legs etc and its not good customer relations to kick the rudder and spill the gin; but seriously it is a problem for cabin crew when the pilots leave their seats in a clumsy manner.

Also there is the issue of the intent of the design. For the ‘Bus’ design the rudder was not intended to either induce or correct roll, i.e. no use of secondary effect. Nor was rudder used for turn co-ordination unless there was a double YD failure. Thus the crew only has to use the rudder on the runway during takeoff or landing, or late in the flare to align the aircraft in a crosswind. Yaw control with engine failure does require rudder input, but even this function in more recent types is automated.

This point emphasizes a growing safety concern due to the gap in the assumptions made by the design and type certification, and those made by the operational certification and in the use of the system by the crew. A typical example is a requirement for the operator to have a policy on the use of automation, who then uses Airbus philosophies in a mixed fleet of Airbus and Boeing aircraft – and the ops cert team agrees with it! So not only do the manufacturers have to cope with differing standards of aircrew behaviors, but also the vagaries of the operational certification and airline training.

This problem in part, ought to be addressed by the proposed joint FAA/JAA AC on human factors, requiring the design to be thoroughly documented, but without requirement to ensure that the design principles or assumptions are transferred to flight training and operations. And even if this does happen there could be several years lag in what should occur and what operators expect to happen.

[Shawn Coyle]

Sort of like the oversight on ETOPS that led to the Airbus flameout and subsequent landing at the Azores - who in the ops department at Transport Canada missed the procedure for flying with crossfeed on automatic when you're supposed to have complete engine isolation???