TYPE : 72 (probably 42 also)
NUMBER / ORIGIN / DATE : 001 / E-mail / 010598
REPORTED x 1
A report has just been received regarding loss of elevator control due to accumulation of de/antice fluid in the tailplane assembly. We hope to have a technical description shortly. THIS IS APPARENTLY A KNOWN PROBLEM !!!. It has been suggested it may be worth ensuring that de/antice fluids are only sprayed on the surfaces, ensuring no prolonged applications are directed at the centre fin/tail mechanism. Ensure full and free movement prior to despatch. Expect increased elevator resistance as fluid runs back during acceleration during T/O roll.
TYPE : 42/72
NUMBER / ORIGIN / DATE : 002 / E-mail / 110598
REPORTED x 1 (Refers to above - ed)
With some anti-icing fluids the flow off on the upper surface of the tail occurs at rotation speed and is triggered by the elevator deflection (shear forces on the fluid layer due to airspeed plus suction effect due to the gap between the stabilizer and the elevator). The fluid flowing through the gap alters the aerodynamic balance of the elevator: the aerodynamic force acting on the elevator, forward of the hinge line is reduced: this results in an increase of the pilot force needed to keep the elevator deflected (partial loss of the offsetted hinge line effect). The additional lift due to the elevator deflection being mainly produced on the stabilizer leading edge, the effect of the gap obstruction on the total lift of the surface is minor (no significant efficiency loss). Normal pilot force is 40lb to obtain minimum rotational deflection. This force can need to be more than doubled when this effect occurs.
The threshold of the pitch disconnect mechanism is set at about 50 daN, that means it must have a difference of this value between left and right elevator to get the activation of the clutch. FDR evaluation of these incidents did not show a risk of disconnection of this system.