Smiths Aerospace
Electronic Systems – Malvern
BOEING B737-100/200/300/400/500
INTRO
Page 1
July
15/02
DOC NO. 0134ED
MAINTENANCE MANUAL SUPPLEMENT
CHAPTER 28 – FUEL
INTRODUCTION
Smiths Aerospace, Inc. designed the Transient Suppression Unit (TSU) to produce an alternate means of
compliance to Airworthiness Directive (AD) 99-03-04 which mandates that operators of Boeing B737
aircraft perform wire separation modification to fuel system wiring. The alternate means of compliance is
achieved by the installation of Smiths Aerospace, Inc. Transient Suppression Units(TSU).
The TSU is inserted in the wiring of the Fuel Quantity Indication System (FQIS) between the in-tank
components (capacitance probes and the compensators) and the Fuel Quantity Indicators located in the
cockpit and refueling stations. The TSUs are installed near where the FQIS wiring enters the tanks and
are intended to prevent any electrical signals, current or voltage, which is capable of igniting fuel vapor,
from entering the fuel tank.
