AMC 25.177(d) Full Rudder Sideslips

ED Decision 2003/2/RM

1.1     At sideslip angles greater than those appropriate for normal operation of the aeroplane, up to the sideslip angle at which full rudder control is used or a rudder control force of 801 N (180 lbf) is obtained, CS 25.177(d) requires that the rudder control forces may not reverse and increased rudder deflection must be needed for increased angles of sideslip. The goals of this higher-than-normal sideslip angle test are to show that at full rudder, or at maximum expected pilot effort: (1) the rudder control force does not reverse, and (2) increased rudder deflection must be needed for increased angles of sideslip, thus demonstrating freedom from rudder lock or fin stall, and adequate directional stability for manoeuvres involving large rudder inputs.

1.2     Compliance with this requirement should be shown using straight, steady sideslips. However, if full lateral control input is reached before full rudder control travel or a rudder control force of 801 N (180 lbf) is reached, the manoeuvre may be continued in a non-steady heading (i.e., rolling and yawing) manoeuvre. Care should be taken to prevent excessive bank angles that may occur during this manoeuvre.

1.3     CS 25.177(d) states that the criteria listed in paragraph 1.1 must be met at all approved landing gear and flap positions for the range of operating speeds and power conditions appropriate to each landing gear and flap position with all engines operating. The range of operating speeds and power conditions appropriate to each landing gear and flap position with all engines operating should be consistent with the following:

a.       For take-off configurations, speeds from V₂+xx (airspeed approved for all-engines-operating initial climb) to V_FE or V_LE, as appropriate, and take-off power/thrust;

b.       For flaps up configurations, speeds from 1.23 V_SR to V_LE or V_MO/M_MO, as appropriate, and power from idle to maximum continuous power/thrust;

c.       For approach configurations, speeds from 1.23 V_SR to V_FE or V_LE, as appropriate, and power from idle to go-around power/thrust; and

d.       For landing configurations, speeds from V_REF-9.3 km/h (5 knots) to V_FE or V_LE, as appropriate, with power from idle to go-around power/thrust at speeds from V_REF to V_FE/V_LE, and idle power at V_REF-9.3 km/h (5 knots) (to cover the landing flare).

2       Full Rudder Sideslips

2.1     Rudder lock is that condition where the rudder over-balances aerodynamically and either deflects fully with no additional pilot input or does not tend to return to neutral when the pilot input is released. It is indicated by a reversal in the rudder control force as sideslip angle is increased. Full rudder sideslips are conducted to determine the rudder control forces and deflections out to sideslip angles associated with full rudder control input (or as limited by a rudder control force of 801 N (180 lbf)) to investigate the potential for rudder lock and lack of directional stability.

2.2     To check for positive directional stability and for the absence of rudder lock, conduct steady heading sideslips at increasing sideslip angles until obtaining full rudder control input or a rudder control force of 801 N (180 lbf). If full lateral control is reached before reaching the rudder control limit or 801 (180 lbf) of rudder control force, continue the test to the rudder limiting condition in a non-steady heading sideslip manoeuvre.

3       The control limits approved for the aeroplane should not be exceeded when conducting the flight tests required by CS 25.177.

4       Flight Test Safety Concerns. In planning for and conducting the full rudder sideslips, items relevant to flight test safety should be considered, including:

a.       Inadvertent stalls,

b.       Effects of sideslip on stall protection systems,

c.       Actuation of stick pusher, including the effects of sideslip on angle-of-attack sensor vanes,

d.       Heavy buffet,

e.       Exceeding flap loads or other structural limits,

f.       Extreme bank angles,

g.       Propulsion system behaviour (e.g., propeller stress, fuel and oil supply, and inlet stability),

h.       Minimum altitude for recovery,

i.        Resulting roll rates when aileron limit is exceeded, and

j.        Position errors and effects on electronic or augmented flight control systems, especially when using the aeroplane’s production airspeed system.