cupdf.com_cdccl-presentation.ppt

Fuel Tank Safety (FTS) /
Airworthiness Limitation (AWL) /
Critical Design Configuration Control
Limitation (CDCCL)

10/20/2022 2
AIRWORTHINESS MANAGEMENT - AVIONICS
BACKGROUND
 TWA B747-131 Fligth-800 accident, involving Centre Wing
Tank (CWT) explosions
 Investigations revealed penetration of 115 Vac electrical
energy into the center fuel tank due to chaffed Fuel Quantity
Indicating System (FQIS) wiring
 Together, with the inadequate electrical bonding of fuel
system Components, separation of fuel system wiring, and
fuel vapors, resulted in loss of the passenger lives and the
airplane.
 Fuel tank explosions can only occur when an ignition
source is in contact with flammable fuel vapor.

10/20/2022 3

10/20/2022 4
FUEL TANK EXPOLSION INCIDENT
March 2001, Thai Airways 737
 CWT fuel pumps left running on when dry. Electrical
ARC / fault resulted in Centre Tank explosion
 airplane was being prepared for a departure to Chiang
Mai
 149 passengers were waiting to board
 The fire erupted into the cabin, killing one cabin crew
member and injuring 6 others
 The fire was put out in 60 minutes
 The airplane was destroyed

10/20/2022 5

10/20/2022 6
FUEL TANK EXPOLSION INCIDENTS
China Air 737-800
 While retracting slats during taxi, one loosened slat
fairing bolt penetrated into the CWT resulting CWT
explosion.

10/20/2022 7
FUEL TANK EXPOLSION INCIDENTS
Philippines Airlines B737 1990
 CWT explosion during push back

10/20/2022 8
COMMON FEATURES OF SIGNIFICANT
ACCIDENTS/INCIDENT
NO IGNITION SOURCE
IDENTIFIED
NO IGNITION SOURCE
IDENTIFIED
NO IGNITION SOURCE
IDENTIFIED
Jet-A1 fuel, approx. 97 degree F
ambient temp.(36’C)
Jet-A fuel, approx. 120 degree
F tank temp.(49’C)
Jet-A fuel, approx. 95 degree F
ambient temp.(35’C)
1 fatality
230 fatalities
8 fatalities
CWT pumps operating at time of
explosion
CWT pumps operating at
time of Explosion
CWT pumps operating at time
Of Explosion
Empty CWT explosion
minutes after refueling
Empty CWT explosion
During climb
Empty CWT explosion
during
pushback from gate
Air Conditioning Packs running
during Ground Operations
10 year old airplane
25 year old airplane
Almost new airplane
2001 - B-737-400 Bangkok,
Thailand
1996 - B-747, TWA 800,
JFK,USA
1990 - B-737-300 Manila,
Philippines

10/20/2022 9
THE “FIRE” TRIANGLE
Fire is a chemical process requires
three things:
 OXYGEN,
 HEAT and
 FUEL
Without one of these elements,
a fire cannot start or continue.
 The process in a fire is called oxidation.
 A fire hazard can be minimized by
eliminating any one side of the fire triangle

10/20/2022 10
REGULATORY ACTION/
REQUIREMENTS
 Special Federal Aviation Regulation 88 (SFAR 88),
advising airplane manufacturers to carry out a design
review of fuel tank system to avoid entry of any ignition
source into the fuel tanks in compliance of FAR 25-901 &
25.981 (a) and (b).
 National Aviation Authorities (NAA) using NT/POL/25/12,
JAR 25.901 / 25.1309 & Technical Guidance Leaflet
(TGL) 47.

10/20/2022 11
SFAR No. 88--Fuel Tank System Fault Tolerance
Evaluation Requirements
Applicability
 the holders of type certificates, and supplemental type certificates
that may affect the airplane fuel tank system, for turbine-powered
transport category airplanes, provided the type certificate was
issued after January 1, 1958, and the airplane has either a
maximum type certificated passenger capacity of 30 or more, or a
maximum type certificated payload capacity of 7,500 pounds or
more.
 This SFAR also applies to applicants for type certificates,
amendments to a type certificate, and supplemental type certificates
affecting the fuel tank systems for those airplanes identified above, if
the application was filed before June 6, 2001, the effective date of
this SFAR, and the certificate was not issued before June 6, 2001.

10/20/2022 12
SFAR No. 88--Fuel Tank System Fault Tolerance
Evaluation Requirements
Compliance
(a) Conduct a safety review of the airplane fuel
tank system to determine that the design
meets the requirements of §§ 25.901 and
25.981(a) and (b).
(b) Develop all maintenance and inspection
instructions
(c) Submit a report for approval to the FAA
Airplane Certification Office (ACO)

10/20/2022 13
FAR §25.981 Fuel tank ignition prevention
a. “No ignition source may be present at each point in the fuel tank
or fuel tank system where catastrophic failure could occur due to
ignition of fuel or vapors.”
b. Critical Design Configuration Control Limitations (CDCCL),
inspections, or other procedures must be established, as
necessary, to prevent development of ignition sources within the
fuel tank system and must be included in the Airworthiness
Limitations section of the Instructions for Continued Airworthiness.
c. The fuel tank installation must include either:
(1) Means to minimize the development of flammable vapors in the fuel
tanks (in the context of this rule, “minimize'' means to incorporate
practicable design methods to reduce the likelihood of flammable
vapors); or
(2) Means to mitigate the effects of an ignition of fuel vapors within fuel
tanks such that no damage caused by an ignition will prevent
continued safe flight and landing.”

10/20/2022 14
THE CONCEPT OF IGNITION SOURCE
PREVENTION
 Fuel tank explosions can only occur when an ignition
source is in contact with flammable fuel vapor.
 Fuel vapors become flammable when they are mixed in
certain proportions with oxygen, and are under specific
temperature and pressure conditions.
 some fuel tanks have a significantly higher exposure to
flammable vapors than other tanks.

10/20/2022 15
PREVENTION
 First Line of Defense to prevent recurrence of such events,
Airplane manufacturer’s reviewed the airplane fuel system
designs to meet the above requirements.
 a number of service Bulletins (SBs) /Production Modifications
(Production Revision Record: PRR) have been introduced for
incorporation on Production and In-Service airplanes, trying to
build the airplane fuel system design immune to such
occurrences.
 FAA legislation requires that airplane types that have fuel tanks,
which exceed the average flammability exposure level (> 7%),
specified in the rule shall be fitted with either a Flammability
Reduction System (FRS), or an Ignition Mitigation Means (IMM).

10/20/2022 16
PREVENTION
 EASA has issued a Safety Information Bulletin (SIB 2010-10)
which mandates the installation of a FRS on production airplane
subject to high flammability exposure and manufactured after
31st December 2011.
 EASA will publish a Notice of Proposed Amendment (NPA) by
mid 2011 to address the in- service airplane retrofit.

10/20/2022 17
PREVENTION
Compliance Target
In relation to the affected airplane, fifty percent (50%) of each operator's
fleet of airplane are to be completed within 4 years of release of the
Service Bulletins i.e. by 2014. One hundred percent (100%) of each
operator's fleet of airplane are to be completed within 7 years after the
release of the Service Bulletins i.e. by 2017.
NOTE: Portable gas detectors are used to monitor Oxygen and flammable
vapor concentrations within the fuel tanks. Oxygen concentrations
should be between 19.5 and 23.5 percent. Level below 19.5 percent is
considered Oxygen deficient, while levels above 23.5 percent will
significantly increase the risk of fire and/or explosion. Monitoring these
figures is critical to the safety of the maintenance crew.

10/20/2022 18
A Flammability Reduction System (FRS)
 FRS is a system that is designed to prevent fuel vapors from
being in a flammable condition
 A practical Flammability Reduction System (FRS) will
reduce fuel tank oxygen content to below the level that will
support combustion (approach being adopted by Airbus).
 Boeing has developed Nitrogen Generation System (NGS)
to satisfy FRS requirement.

10/20/2022 19
An Ignition Mitigation Means (IMM)
 IMM is a system that detects an ignition source and releases
a fire suppressant to prevent the development of a fire.
 Such a technology is used on small military airplane but is not
considered sufficiently robust for use in large commercial
airplane and as such is not being pursued by Airbus or
Boeing.

10/20/2022 20
CHANGES TO “INSTRUCTIONS FOR
CONTINUING AIRWORTHINESS” (ICA)
 Second Line of Defense of the FTS regulations account for this
situation and requires updating of Instructions for Continued
Airworthiness (ICA) / Airplane Maintenance Program for all the
type certificated airplane to avoid any likelihood of compromise /
violation of the fuel system design criteria during any scheduled
and / or unscheduled maintenance.
 This requirement ensures proper documentation of any
maintenance action performed on the airplane and / or its
components for safety, reliability and maintainability.
 AWL / CDCCL tasks were introduced by airplane manufacturers
in Maintenance Planning Documents AND have already been
incorporated into the PIA’s fleet maintenance program.

10/20/2022 21
CHANGES TO “INSTRUCTIONS FOR
CONTINUING AIRWORTHINESS” (ICA)
 Boeing MPD section-9 is related to Airworthiness Limitations
(AWL) which describes the Fuel Airworthiness Limitation Items
(ALIs) and the associated CDCCL tasks.
 Airbus / ATR publishes “Airworthiness Limitations” (ALS) section
-5 which is related to Fuel Airworthiness Limitations (FAL). These
requirements, together with the Life Limits / Monitored Parts,
structural Airworthiness Limitation Items (ALI) and systems
Certification Maintenance Requirements (CMR) comprise the
Airworthiness Limitation Section which satisfies the regulatory
requirements.

10/20/2022 22
Airworthiness Limitation Items (ALIs)
 ALIs identify inspection tasks related to fuel tank ignition source
prevention which must be done to maintain the design level of
safety for the operational life of the airplane.
 These ALIs are mandatory and cannot be changed or deleted
without the approval of applicable regulatory agency.
 Strict adherence to methods, techniques and practices as
prescribed is required to ensure the ALI is complied with.
 Any use of methods, techniques or practices not contained in
these ALIs must be approved by the applicable regulatory
agency.

10/20/2022 23
Limitations (CDCCLs)
 CDCCLs are a means of identifying certain design configuration
features intended to preclude a fuel tank ignition source for the
operational life of the airplane.
 CDCCLs are mandatory and cannot be changed or deleted
without the approval of the applicable regulatory agency.
 “A critical fuel tank ignition source prevention feature may exist in
the fuel system and its related installation or in systems that, if a
failure condition were to develop, could interact with the fuel
system in such a way that an unsafe condition would develop
without this limitation.”

10/20/2022 24
Limitations (CDCCLs)
 Strict adherence to configuration, methods, techniques, and
practices as prescribed is required to ensure compliance with the
CDCCL.
 Any use of parts, ,methods, techniques or practices not
contained in the applicable CDCCL must be approved by the
FAA office that is responsible for the airplane model Type
Certificate, or applicable regulatory agency.

10/20/2022 25
Certification Maintenance Requirements
(CMRs)
 A CMR is a required periodic task, established during the
design certification of the airplane as an operating limitation
of the type certificate.
 CMRs usually result from a formal, numerical analysis
conducted to show compliance with catastrophic and
hazardous failure conditions.

10/20/2022 26
Sample of AWL / FAL for B777

10/20/2022 27
Sample of AWL / FAL for A310
CDCCL Requirement Reference Applicability
1 Air gap between a fuel
quantity indicating
probes and the
airplane structure.
Critical to prevent spark
generation
during lightning strike conditions
and must not be compromised
The gap stated in the relevant
maintenance procedure in the
AMM
must be achieved during
installation of a fuel quantity
probe.
AMM
28-42-31 pb 401
28-42-32 pb 401
28-42-33 pb 401
ALL
ALL
ALL
2 Separation of fuel
quantity and level
indicating system
wiring from other
wiring.
To prevent cross coupling of high
voltage transients and thereby
keep
unsafe ignition energies from
inside the tank it is required that
operators obey the wire routing
and separation standards given in
the Electrical
Standard Practices Manual
(ESPM).
ESPM
20-10-00
20-33-20
20-33-21
20-33-22
ALL
ALL
ALL
ALL

10/20/2022 28
3 Direct bonding on
items of equipment
inside a fuel tank.
Direct bonding is critical to
prevent
spark generation during
component
failure and lightning strike
conditions and must not be
compromised Direct bonding in
fuel tanks must be carried out
during component installation to
the appropriate bonding method
and standard stated within the
installation procedure in the AMM.
AMM
28-00-00 pb 401
28-11-21 pb 401
28-11-22 pb 401
28-11-24 pb 401
28-11-32 pb 401
28-12-21 pb 401
28-12-33 pb 401
28-12-34 pb 401
28-21-13 pb 401
28-21-21 pb 401
28-24-31 pb 401
28-25-15 pb 401
28-27-12 pb 401
28-43-21 pb 401
28-46-21 pb 401
ALL
ALL
ALL
ALL
A310-300
ALL
A310-300
A310-300
ALL
ALL
ALL
ALL
A310-300
ALL
ALL

10/20/2022 29
4 Safety critical
features of fuel
pumps
These features must be maintained
throughout the full life of the fuel
pump to avoid the possibility of
generation of an ignition source by
overheating or sparks caused by
arcing, friction etc.
Repair and overhaul of fuel pumps
must be carried out in accordance
with the equipment manufacturer’s
maintenance instructions or other
maintenance instructions
acceptable to the certifying
authority.
CMM
28 09 01
28 24 11
ALL
ALL

10/20/2022 30
MANAGEMENT / CONTROL OF CDCCL
 Refer Doc ref # PIA/CDCCL/SFAR88 for detailed procedure
for the Management & Control of CDCCL in PIA.
 It is the responsibility of certifying staff / maintenance
personnel to ensure that the above stated CDCCL
configurations are maintained to reduce the risk of any
ignition source penetration into the fuel tank (s).
 If any of these CDCCL is compromised, this may lead to wire
chaffing, fault current (short circuit), or overheating of the
CWT fuel pumps.
 This in turn may result in fuel tank explosion.

10/20/2022 31
 Dry running of the fuel pumps should not be allowed as it
has already resulted in catastrophic incidents.
 This requirement has been addressed both by Airbus &
Boeing by introduction of new logic circuitry to avoid dry
running on CWT fuel pumps.
 Introduction of Ground Fault Interrupter (GFI) relays also
ensures NO overheating / fault current in the fuel pump
circuitry.

10/20/2022 32

10/20/2022 33
OVERHAUL SHOP CONTROL FOR
CDCCL
 Fuel pumps CMM have also been revised in compliance of
CDCCL requirements and provides specific instructions /
procedures.
 Tools, kits, jigs, materials, test equipment required for
servicing, repair or overhauling of a fuel system component
should be used accordingly.

10/20/2022 34

10/20/2022 35
AD/ SB Control for CDCCL
 AD/SB evaluation check list was updated to include a clause
to check whether the literature under evaluation affects
CDCCL or not.
 Certifying staff / maintenance personnel should assess the
affect of the current activity on any of the AWL/CDCCL, and
if, it is confirmed that a CDCCL / AWL is directly or indirectly
affected, work instructions provided by the AD / SB or task
card should be revised / corrected in coordination with
Airworthiness Management Division to preclude any chance
of CDCCL violation.
 A data base will be updated to have a record of all the ADs,
SBs, and ECO which have an effect on any of the CDCCL
requirements.

10/20/2022 36
Scheduled / unscheduled repair schemes control
 Any scheduled /un-scheduled locally prepared repair
scheme should be examined for effect on any of the CDCCL
item(s).
 Same level of understanding is required by shop personnel
involved in the servicing / repair / overhaul of Fuel pumps,
FQI Tank unit, Fuel Quantity Indicating Computer (FQIC),
Fuel Quantity Processor Unit (FQPU), harnesses.

10/20/2022 37
Maintenance Program Control for CDCCL
 Inspections/ tasks introduced through Locally generated
task cards as per requirements of an AD, inspection SB, or
any other local operational /maintenance requirement also
requires assessment whether it affects the CDCCL or not.
 PIA fleet Maintenance program should be scrutinized on a
regular basis upon receipt of MPD revision, to sort out the
newly introduced tasks for having an impact on the CDCCL.
 This exercise should be continued in future as well.

10/20/2022 38
MAINTENANCE DATA - MANUAL
CONSULTATION
 Use of updated / latest maintenance data is of utmost
importance for maintaining FTS design criteria / CDCCL.
 Air Transport Association of America (ATA) Chapter 47 has
been assigned for FRS / NGS in concerned airplanes
Airplane Maintenance Manuals (AMM).
 CDCCL warning notes have also been introduced in AMM
and Components Maintenance Manuals (CMM).
 All certifying staff / maintenance personnel are required to
consult concerned AMM /CMM (as applicable).

10/20/2022 39

10/20/2022 40

10/20/2022 41

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