What was found
INVESTIGATED PILOT REPORT OF UNCOMMANDED "SPEEDBRAKE EXTENDED" ANNUNCIATOR LIGHT ILLUMINATION IN FLIGHT. FOUND HIGH RESISTANCE IN SPOILER MIXER ASSY. SPEEDBRAKE RETRACT SWITCH ASSY, REPLACED S156 SWITCH WITH SUPERSEDING PN 21EN42-6 SWITCH ASSY. SPEEDBRAKE SYSTEM OPERATIONS NORMAL, NO FAULTS INDICATED. SUSPECT S156 SWITCH CONTACTS CORRODED OR PITTED FRO WEAR AND/OR LONGTERM WATER/DIRT CONTAMINATION. RECOMMEND SIMILAR SWITCHES ON BE 400 SERIES AIRCRAFT BE REPLACED WITH IMPROVED SWITCHES WITH BETTER SEALING CAPABILITIES BY RECOMMENDED SERVICE BULLETIN OR SIMILAR. (K)