For many years, commercial airplanes have relied on oxygen deprivation
to control the risk of cargo-compartment fires below the main passenger
cabin. However, a cargo fire in a commercial airplane that resulted in
hull loss has caused the perception of cargo-fire risk to grow. In response,
the U.S. Federal Aviation Administration (FAA) issued a rule change on
March 18, 1998, that mandates the conversion of Class D compartments to
Class C or Class E compartments by installing smoke-detection systems,
fire-suppression systems, or both.
Boeing is positioned to help commercial airplane operators meet the rule
change deadline of March 18, 2001. The Boeing support plan is based on
and recent use of Class D compartments.
criteria for Class C compartments.
criteria for Class E compartments.
assistance available to operators.
and validated design.
(Boeing has developed retrofit kits for operators of Boeing-designed
commercial airplanes and the Douglas DC-10. Operators of other Douglas-designed
airplanes may contact their local Boeing Field Service representative
or regional FAA office for information on purchasing retrofit kits from
various suppliers. These kits are available for the DC-8, DC-9, MD-80,
and MD-90. Operators may also contact their regional FAA office for information
on approved suppliers for these kits.)
Class D compartments, which are minimally ventilated cargo holds that
are 1,000 ft3 (28.3 m3) or less, have been used
in smaller commercial airplanes that fly short to medium routes. These
compartments contain primarily passenger luggage and present a low ignition
hazard. Reduced oxygen at cruising altitudes further lowers the likelihood
of sustained combustion in the cargo compartment.
However, with the growth of air cargo as a revenue source, the mix of
items and materials carried in cargo compartments has changed. Commercial
products, industrial materials, and airplane components en route to airline
maintenance stations have joined baggage below the passenger cabin. Though
the compartments are designed and required to be free of ignition sources,
the risk that a sequence of events involving human error could lead to
a fire is perceived to have increased.
Boeing- and Douglas-designed commercial airplanes that have Class C compartments
are shown in table
1. These compartments contain both the smoke-detection and fire-suppression
equipment required by the new FAA rule.
Current specifications for Class C compartments require that the smoke-detection
system alert the flight crew within 60 sec from the time smoke first appears
in the compartment.
Current specifications for the fire-suppression system in each Class C
compartment require a minimum initial concentration of 5 percent Halon
throughout the compartment to suppress any combustion to controllable
levels. Thereafter, the system must sustain a minimum concentration of
3 percent Halon for 60 min to prevent reignition or spreading of the combustion.
For airplanes certified for extended-range twin-engine operations (ETOPS),
the fire-suppression system must be able to sustain a 3 percent concentration
of Halon within the compartment for a maximum of 180 min (fig.
Boeing-designed commercial airplanes that have Class E compartments are
shown in table 1. These compartments
contain the smoke-detection equipment required by the new FAA rule for
in-service airplanes. Current specifications for Class E compartments
require that the smoke-detection system alert the flight crew within 60
sec from the time smoke first appears in the compartment.
Boeing and several airplane system suppliers have developed retrofit solutions
to help operators comply with the new FAA rule. Boeing offers these solutions
in two main forms:
- Service bulletins.
- Retrofit kits.
Boeing has prepared service bulletins for all affected Boeing-designed
commercial airplanes, including the 727-100/-200 and all 737s except the
737-900. Operators have the option to obtain a supplemental type certificate
for their own designs manufactured under contract to a supplier.
In anticipation of operator needs, Boeing completed the development and
engineering for service bulletins for all affected Boeing-designed commercial
airplanes in September 1997. Experience developing smoke-detection and
fire-suppression systems for other Boeing models significantly benefited
the systems' design.
The service bulletins give operators information to route wires and tubing,
mount Halon bottles, and locate circuit breakers and the flight-deck control
panel in accordance with their own airplane configurations (fig. 2). Operators may request
a master change if they would like Boeing to develop customized service
bulletins to reflect the unique configurations of their airplanes.
The service bulletins include
- Complete installation details for detectors, suppression nozzles,
cargo electronic units fire suppression bottles, and flight deck control
- Wire and tube routing information.
- Detailed information on connectors and fittings, type and size of
wiring and tubing, tube bending and splicing criteria, and wire separation
criteria and wiring schematics.
- Ground rules governing areas not covered in detailed installation
- List of approved smoke detector and fire bottle part numbers and suppliers.
Boeing also offers for purchase a retrofit kit that can be used either
by operators performing the installation at their own maintenance centers
or by commercial modification centers that install systems for operators.
Boeing demonstrated a retrofit system on a 737-400 airplane as part of
the certification process. Elements of these installations were applied
to the development of the fleet retrofit kits.
When beginning the effort to provide operators with the information and
hardware necessary to comply with the FAA rule change, Boeing considered
The smoke-detection retrofit design for the 727 and 737 airplanes is a
dual-loop photoelectric system (fig.
3) that has been demonstrated to detect smoke from any location in
the forward or aft cargo compartment within the specified 60-sec limit.
The dual-loop system reduces the incidence of false reports by requiring
that at least one sensor in each loop detect smoke simultaneously before
the annunciator on the flight deck is activated. If power loss prevents
either loop from functioning, the system will automatically reconfigure
to transmit a warning upon detection of smoke by the sole remaining detection
loop. Failure of a single detector in either loop will leave the remaining
detectors in the loop functional and capable of detecting smoke anywhere
in either cargo compartment within the 60-sec limit.
Flight-deck indicators and controls for the system are located on the
center-aisle stand for the 737 and the overhead panel for the 727. The
service bulletins will allow operators to install the control panel in
alternate locations on the flight deck.
The indication and control panel includes the following:
- Detector select switch.
- Cargo fire test switch.
- Detector fault indicator.
- Master fire warning light and bell.
- Cargo fire warning lights and armed switches.
- Extinguisher test lights.
Detector select switch.
The detector select switch is a three-position rotary switch marked A,
B, and NORM. The flight crew uses the switch to command FWD or AFT single-loop
(A or B) operation or normal dual-loop (NORM) operation of the detection
Cargo fire test switch.
The TEST switch is a pushbutton that verifies the operation of all detectors
in both cargo compartments and the suppression system. When the system
is functioning normally, depressing the switch causes the FIRE WARN light
and the red FWD and AFT indicators to illuminate, the warning bell to
sound until the test button is released, the extinguisher test light to
illuminate, and the cargo fire bottle DISCH lights to illuminate.
Detector fault indicator.
A faulty detector will cause the amber DETECTOR FAULT indicator to illuminate
and the FWD or AFT indicator to fail to light, depending on which compartment
contains the faulty detector. The flight crew can determine whether the
A or B loop contains the fault by selecting position A or B on the detector
select switch. When the properly functioning loop is selected, the DETECTOR
FAULT indicator will not light, and the FWD and AFT indicators will both
illuminate under test. The DETECTOR FAULT indicator will also illuminate
if the selected loop loses power after the test switch is depressed. The
airplane can be flown under master minimum equipment list procedures with
the single-loop position selected for either the forward or aft compartments.
The airplane operations manual will require the flight crew to perform
these tests before the first flight each day to prevent detector faults
from being unrecognized for more than one day.
Master fire warning light and bell.
Upon detection of smoke, a fire warning bell will sound, the cargo fire
warning light on the control panel will illuminate, and the appropriate
red location indicator will specify if the smoke is detected in the forward
or aft compartment.
Cargo fire warning lights and armed switches.
The cargo fire warning lights illuminate red when smoke is detected in
the forward or aft compartment. Pressing the illuminated FWD or AFT indicator
causes the upper half of the indicator to illuminate ARMED in white. This
indicates that the system is ready to discharge suppressant into the indicated
compartment. Depressing the guarded DISCH pushbutton switch releases the
suppressant into the selected compartment. Once Halon has been discharged
to the respective cargo compartment, the control panel DISCHARGE light
will illuminate red.
Extinguisher test lights.
A bottle in the air-conditioning mix bay between the forward and aft cargo
compartments contains Halon 1301. The Halon bottle can discharge to either
compartment, but once activated, the system cannot be reversed to the
other compartment. A sensor detects Halon bottle pressure and activates
the Halon low-pressure indicator on the flight deck when the bottle discharges
or loses pressure.
The TEST switch checks the condition of the discharge nozzles in both
compartments. The FWD and AFT indicators illuminate green when the system
is functioning normally. Airplanes may not be dispatched with a loaded
cargo compartment if the fire-suppression system exhibits any faults.
Boeing began installing smoke-detection and fire-suppression systems into
737 production airplanes at line position 3078 for the 737-300/-400/-500
models and at line position 91 for 737-600/ -700/-800 models. The production
deliveries also include 195-min ETOPS configurations. (The 195 min allows
for 180-min ETOPS diversion followed by 15 min for missed approach and
emergency passenger evacuation.)
To support operators in retrofitting their airplanes, Boeing has developed
modification kits, including revised documentation and the respective
service bulletins. The Boeing portion of the kits will include all hardware
for installing the detection and suppression systems, including suppression
tubes, wire bundles, support brackets, detector pans, suppression pans
and nozzles, and all standard-type hardware. An additional buyer-furnished
equipment (BFE) hardware kit will also be required. The retrofit system
uses the same components as the production system. Table 2 identifies the respective
model, service bulletin, and anticipated weight increase associated with
The retrofit 737-300/-400/-500 service bulletin package will include
multiple configurations, including auxiliary fuel cellconfigured
and ETOPS-equipped airplanes. Auxiliary fuel cell configurations include
aft cargo compartment single Boeing fuel cells, single Rogerson fuel cells,
and dual Rogerson fuel cells. These unique configurations will be identified
as separate groups within the service bulletin. ETOPS-equipped airplanes
will have a second 33-lb Halon bottle installed on the opposite side of
the mix bay.
Boeing has identified five different suppliers for the BFE kits and has
qualified hardware from each supplier. Four suppliers have been qualified
to provide smoke detectors (fig. 4) for Boeing-designed
airplanes. All four detectors are considered interchangeable and intermixable.
Additionally, Boeing has qualified two Halon bottle sources. The cargo
electronics units and flight-deck control panel are considered single-source
items. Boeing suggests that operators contact individual manufacturers
for BFE kits.
To ensure that the Boeing-supplied and BFE kits meet installation requirements,
Boeing has completed service bulletin validations on the 737-200/-300/-400/
-500. The 727-200 validation is expected to be completed in early 1999.
The company is in the process of determining the method of validation
when the 737-600/ -700/-800 bulletins become available.
Boeing has developed a comprehensive plan to assist operators in meeting
a new FAA rule to convert Class D cargo compartments to Class C or Class
E compartments. To help operators comply with the March 18, 2001, deadline
to install smoke-detection systems, fire-suppression systems, or both
in existing Class D compartments, Boeing has completed the necessary steps
to support the in-service fleet of Boeing-designed commercial airplanes.
Those steps include the certification efforts, system design, service
bulletin validations, and kit development to make Class D compartments
compliant with Class C or Class E specifications.
Boeing Commercial Airplanes Group