CASA AWB 26-1 Issue 1

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.

FMI: http://www.casa.gov.au/avreg/aircraft/AWB/26/001.htm, AirworthinessBulletin@casa.gov.au