ILF 402, 452, 509, 510, 523, 525-528, 568, 569, 576, 577, 581, 583, 585, 588-590, 592-599, 601-603, 606, 607,
610-615, 620, 625-627, 691-699, 833-835, 838, 971, 980-999; ILF 101, 151, 156-199, 301, 304, 308, 310, 314, 315,
317-319, 323, 331-399, 401, 405, 406, 409, 410, 412, 416, 424, 425, 427-429, 451, 501-504, 507, 508, 512-514,
516, 518, 524, 531-533, 535-537, 541, 542, 552-556, 560-562, 567, 571-575, 671, 672, 686, 703, 707-710, 803-813,
821, 822, 831, 832, 836, 837, 841, 842, 851, 852, 854-858, 861-863, 871-874, 947, 948, 968-970, 972, 973 POST
SB 737-47-1003
TASK 47-00-00-010-801
3. Nitrogen Generation System (NGS) Precautions
(Figure 201)
A. General
(1) This task has these procedures:
(a) Physiological Effects of a Low Oxygen Content Environment
(b) Fuel Tank Entry Precautions
(c) Air Conditioning Compartment Precautions
(d) Main Wheel Well Precautions
(e) Nitrogen Generation System Maintenance Precautions
(f) Air Separation Module Precautions
(2) The NGS is an inert gas system that decreases the flammability of the center tank. Fresh air
contains approximately 78% nitrogen and 21% oxygen. The NGS separates the nitrogen and
oxygen into nitrogen-enriched air (NEA) and oxygen-enriched air (OEA). NEA increases the
nitrogen content and decreases the oxygen of the air. If you breathe air that does not have
sufficient oxygen, health problems can occur. Obey the precautions in this procedure if you do
maintenance in an area where you could breathe air that does not have sufficient oxygen.
(3) The NGS components are found in the air conditioning compartment on the left side of the
airplane. Access to the thermal control unit and air separation module (ASM) is through access
door 192BL. The nitrogen enriched air distribution system (NEADS) line is attached to the ASM
and is routed to the center tank through the left wheel well. The NEADS line has 1/2 inch
aluminum tubing, a dielectric hose, a flame arrestor, check valves, and an ejector nozzle.
(4) The usual operation of the nitrogen generation system will cause the air inside the fuel tanks to
have a decreased oxygen content. Do not breathe the air in a fuel tank unless that tank is fully
ventilated. Procedures for fuel tank purging and entry on airplanes equipped with a nitrogen
generation system are given in Chapter ATA 28, Fuel Systems. Danger stencils and placards
are installed adjacent to fuel tank access doors to warn you of the hazards that can occur if
you breathe air with low oxygen content.
(5) NEA that is generated by the air separation module (ASM) is routed safely to the center tank.
The usual operation of the nitrogen generation system outside of the fuel tanks is free from
concentrations of NEA. However, a duct leak, or component failure can cause NEA to go into
areas outside of the fuel tanks. An NEA leak can cause a condition where the oxygen content
of the air is decreased. Caution stencils and placards are installed on access doors adjacent to
areas where potential NEA leakage can occur.
(6) If you make a decision not to do this recommended procedure, you must have an approved
alternate procedure. Make sure the conditions during maintenance operations give sufficient
protection to the persons and equipment used in this procedure. It is possible that local fire
codes, and standards make it necessary to use more restrictive procedures or more
procedures than those given in this procedure.
737-600/700/800/900
AIRCRAFT MAINTENANCE MANUAL
47-00-00
Page 203
D633A101-ILF Oct 15/2019
ECCN 9E991 BOEING PROPRIETARY - Copyright © Unpublished Work - See title page for details
EFFECTIVITY
ILF 402, 451, 452, 494-500, 503, 504, 509, 510, 514, 523-528, 541, 560-564, 567-569, 574-577, 581, 583, 585,
588-590, 592-599, 601-603, 606, 607, 610-615, 620, 625-627, 671, 672, 691-699, 832-835, 838, 856-858, 947,
948, 968-973, 980-999; ILF 101, 151, 156-199, 301, 304, 308, 310, 314, 315, 317-319, 323, 331-399, 401, 405,
406, 409, 410, 412, 416, 424, 425, 427-429, 501, 502, 507, 508, 512, 513, 516, 518, 531-533, 535-537, 542,
552-556, 571-573, 686, 703, 707-710, 803-813, 821, 822, 831, 836, 837, 841, 842, 851, 852, 854, 855, 861-863,
871-874 POST SB 737-47-1002 OR POST SB 737-47-1003 OR POST SB 737-47-1015; ILF 491-493, 515,
519, 520, 530, 557, 559 POST SB 737-47-1002 OR POST SB 737-47-1015
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