AD 72-20-03

72-20-03 BEECH: Amendment 39-1524. Applies to Models 65-90, 65-A90 and B90 (Serial Numbers LJ-1 thru LJ-501) airplanes and to Models 99, 99A, A99A and B99 (Serial Numbers U-1 thru U-151) airplanes.

Compliance: Required as indicated, unless already accomplished.

To prevent heater overheat which melts the windshield defroster ducting, damages wiring beneath the instrument panel and fills the cabin with smoke, accomplish the following:

A) Effective immediately, operation of the heater is prohibited if the ventilation blower is not functioning.

B) Prior to each flight determine that the ventilation blower is operating.

NOTE: This determination may be made by checking for air flow out of the air distribution openings in the cockpit and/or by the sound of the blower.

C) Within 25 hours' time in service after the effective date of this AD:

(1) Remove and replace existing vent blower and combustion differential switches with Beech P/N 90-380010-1 differential pressure switches in accordance with Beechcraft Service Instructions No. 0500-412 or later revision.

(2) Inspect the heater fuse to determine that a standard fuse of proper value is installed and if an improper fuse is found, prior to further flight, install standard fuse of proper value.

NOTE: Beechcraft Service Instructions No. 0500-412 or later revision lists proper fuses.

D) When Paragraph C has been complied with the limitation in Paragraph A may be removed and the check required by Paragraph B may be discontinued.

E) Any equivalent method of compliance with this AD must be submitted to and approved by the Chief, Engineering and Manufacturing Branch, FAA, Central Region.

This amendment becomes effective September 27, 1972.