Subject:
Engine bleed air warning system installation in Beech turboprop
aircraft.
Effectivity: This Airworthiness Bulletin
relates to the bleed air warning system installed on Beech King Air
200, 300 and 350 series aircraft. However, other Beech turboprop
models using similar systems may also be affected.
Purpose: The purpose of this Airworthiness
Bulletin is to advise operators and maintainers that a possibility
of cross connecting the left and right bleed air warning system may
exist in Beech turboprop aircraft. A cross connected bleed air
warning system can lead the crew to mis-identify a bleed air duct
leak and isolate the wrong system.
Preventive
measures: Maintenance manuals for Beech 200, 300 and 350
aircraft contain procedures to confirm correct operation of the
warning system on the ground by simulating a break in the EVA
tubing. This can be accomplished by disconnecting the tubing from
the bleed air pressure source during operation of the system. When
the left EVA tube is disconnected from the pressure source, the
left switch should activate and illuminate the L BL AIR FAIL
annunciator. Confirmation of the right system operation can
subsequently be accomplished by disconnecting the right tube from
the pressure source. The applicable aircraft maintenance manual
procedure should be followed for testing the system.
Recommendation: Because of the potential danger
associated with the incorrect detection of a failed bleed air
system - operators and maintainers are advised to:
check for possible cross connection of the pressure switches in
the aircraft in accordance with the maintenance manual.
be careful during maintenance so that the pressure switches are
not cross connected inadvertently.
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