Wichita, Kansas USA
Service Bulletin
December 1, 2008
Page 1 of 2
SB MD421-01
SB MD421-01
Emergency Power System
MD420 System: MD421 Module
Modification 1
Eliminates potential for pitot/static leaks
1. DESCRIPTION
A. Effectivity:
This service bulletin is applicable to the Battery Module, p/n MD421 of the MD420 Series of
Emergency Power Systems manufactured by Mid-Continent Instrument Co., Inc. These updates
are installed by the manufacturer and are not eligible to be modified by any entity other than the
manufacturer. Units with this modification are available for sale from the manufacturer and field
units are eligible for update as of December 1, 2008. All units produced from this date forward will
contain the modification. The units are identified by Modification Status 1 as shown on the
nameplate.
B. Reason:
This update is intended to enhance the air speed sensing portion of the unit such that potential
leaks can be avoided which may have been created either during manufacturing or in the field.
C. Description:
Changed the specification of the air tubing internal to the unit and added features to prevent the
twisting of the external air fittings.
D. Compliance:
Optional.
E. Approval:
TSO approval not affected
RTCA DO-160 environmental qualification not affected
F. Weight and Balance: No change.
G. Electrical load data: No change.
H. Other Publications affected:
MD420 Series, Installation Manual and Operating Instructions (p/n 9016391), Revision H
