AD NUMBER: 2010-09-02

MANUFACTURER: British Aerospace Regional Aircraft Model Jetstream Series 3101 and Jetstream Model 3201 Airplanes
SUBJECT: Airworthiness Directive 2010-09-02

BAE Systems have received three reports of uncommanded flap extensions affecting different Jetstream 31 aeroplanes. In one instance, the airplane exceeded the airspeed limit allowed for the uncommanded flap configuration, resulting in damage to the wing trailing edge.

Following investigation, it was considered that a loss of electrical signal to the `up' solenoid of the flap selector valve had occurred and, combined with the normal internal leakage in the hydraulic system, resulted in hydraulic pressure being supplied to the `down' side of the flap hydraulic jack. The loss of signal could have been intermittent, and the evidence strongly implicated oxide debris contamination of the flap selector switch contacts.

This condition, if not corrected, could lead to further cases of damage to the aeroplane due to airspeed limit exceedance, possibly resulting in asymmetric flap deployment, which could lead to loss of control of the airplane.

FMI: http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAD.nsf/0/F26784A16685E02986257714004A731B?OpenDocument