GOVERNMENT OF INDIA CIVIL AVIATION REQUIREMENTS
CIVIL AVIATION DEPARTMENT SECTION 2 - AIRWORTHINESS
SERIES 'S' PART I
ISSUE III,DATED 16TH OCTOBER '1982
File No. 5/343/79-AI(2) EFFECTIVE : FORTHWITH
Subject : Storage conditions and storage/service life of Rubber
parts and aircraft components containing rubber parts.
This part of Series 'S' of Civil Airworthiness Requirements
specifies the procedure concerning storage conditions and
storage/service life in respect of rubber parts and aircraft
components containing rubber parts, which are required for
use on civil aircraft. These are general requirements and
should only be followed in the absence of any specific
requirements from the manufacturers of the aircraft part or
component concerned.
STORAGE CONDITIONS
General requirements :
1. The aircraft parts must be stored in a clean and well
ventilated room. Unusually heavy and long parts should be
adequately supported, while in storage, so that maintain
the intended shape without strain. Manufacturers'
instructions in this regard should be followed.
Tyres should be stored vertically in racks having support
tubes, so that each tyre is supported at two points on the
tread. This support tubes should be close enough so that
major portion of the tyres is above the tubes. The tyres
should be turned to a new position every three months or so.
Aircraft hoses and hose assemblies should be stored uncoiled
and supported so as to release stresses.
2. Temperature : The storage temperature should be between 50
deg. F and 70 deg. F and the distance between the stored
articles and the source of heat should be more than 3 feet.
3. Humidity : The relative humidity in the store room should
be around 65 per cent.
4. Light : Rubber parts should not be exposed to strong light
e.g. direct rays of sun. The store rooms should be kept as
dark as practicable.
5. Oxygen : Isolation from atmospheric oxygen greatly increases
the storage limiting period of rubber parts. Where possible
parts should be racked in airtight containers, or wrappings
and liberal use of talc or french chalk is also recommended.
If parts are packed in airtight tins, they should be lined
with wax paper or polythene to avoid direct contact with the
metal.
6. Ozone : Exposure to air containing ozone even in minute
quantities, should be avoided. Storage rooms should not
contain any apparatus that is capable of generating ozone,
such as high voltage electrical equipment, electric motors
or other plant which may give rise to electric sparks. Free
access to outdoor air, which in temperate climate always
contains ozone, should be avoided. Still indoor air is
normally ozone-free because most wall and ceiling coverings
and organic materials rapidly destroy ozone.
7. Deformation : Rubber parts should, wherever possible, be
stored in a 'relaxed' position free from compression or
distortion, and in all cases with the least possible
deformation, since deformation greatly aggravates the action
of ozone and can also lead to permanent changes in shape and
dimensions. Articles received pre-packed in a strain free
condition can, with advantage, be stored in their original
packing. Spring loaded seals should, if stored for any
length of time, have the spring removed.
8. Contamination : Rubber parts should not come in contact with
liquids or vapour concentrations of any kind during storage
even though they may be subsequently used in contact with a
similar fluid. Contact with copper, brass or rusty iron, or
with any compounds of manganese, should be avoided.
HOSES : STORAGE AND SERVICE LIVES
9. The storage and service life of aircraft/engine hoses
should be normally guided by the manufacturer's
recommendations. Whenever such information is not available
the following instructions should be adhered to.
The hoses have been classified in two groups :
GROUP A : Fuel, Oil, pneumatic and hydraulic pressure
hoses.
GROUP B : All other hoses like hydraulic return line
and instruments hoses etc.
Shelf Life :
10. The total storage/shelf life of both types of hoses shall be
limited to 10 years from the cure date of manufacture
provided they are stored under standard conditions of
storage.
11. During storage, periodic inspection should be carried out
once a year for signs of deterioration, weather cracks,
signs of corrosion on end fittings etc. and hose pressure
tested to 1-1/2 times the working pressure every two years.
12. Before installation on aircraft pressure test should be
carried out at 1-1/2 times the working pressure.
Service Life :
13. Several factors determine the service life of aircraft
system hoses. In some cases the service life is fixed by
the manufacturers taking into consideration the specific
applications. Wherever such information is available, this
should be followed. In the absence of such information
initial life of hoses should not exceed 4 years to start
with for Group A hoses and 6 years for Group B hoses.
Thereafter the service life of the hoses can be developed to
6 years for Group A hoses and 8 years for Group B hoses
subject to accomplishment of the following life development
programme as per the procedure given below :-
(a) Critically examine all the hoses in question for life
development for external defects such as:-
(i) rubber coating or protective shields separating
from the inner tube or from the metal core.
(ii) Hardening or lack of flexibility.
(iii)Evidence of ageing cracks, kinks, chaffing,
blisters and poor condition of the unions.
(b) (i) Subject the hoses to a full specifications test,
for the purpose of life escalation.
(ii) If full specification tests are not spelt out for
the particular hose, subject these to any other
rigorous test, specified by the manufacturer.
(iii)In absence of any reference on items (i) & (ii)
above, subject one sample hose each from different
batch of the hoses in storage to destructive test
to determine its life for escalation.
(iv) If none of the above tests are feasible, due to
non availability of specific recommendations the
hoses may be pressure tested twice the operating
pressure and retained at the elevated pressure for
five minutes and checked for external visible
signs of cracks/damages/deformity etc. for
determination of escalated life.
(c) Hoses passing tests at (a) & (b) above may be
permitted to operate under the life development
programme with the escalated life in the respective
group, i.e. 4-6 years in case of Group 'A' and 6-8
years in the case of Group 'B' with the prior
concurrence of the Regional/Sub-Regional Airworthiness
Office.
Note : Any hose whose identification is impossible or
questionable shall not be considered for life
development programme.
RUBBER PARTS, VALVE SEATS, SEALS ETC.
IN HYDRAULIC AND PNEUMATIC SYSTEM COMPONENTS
Shelf Life :
14. Except where otherwise stated or specified by the
manufacturers, storage/shelf life of rubber parts for
hydraulic and pneumatic components shall be limited to 6
years from the cure date provided they are stored under
standard conditions of storage. The date of cure should be
available on the original documents from the makers. Rubber
parts/seals which have been stored for more than 4 years
should be subjected to detailed examination and stretch test
prior to use as indicated below :
(i) Seals which give evidence of hardening or softening,
blistering or peeling should be discarded.
(ii) A sample seal from each batch should be checked for
deterioration by stretching the seal to 20% of their
internal diameter. If cracks are visible under X10
magnification, the seals should be rejected.
Service Life :
15. In case the manufacturers have fixed the service life of
components and such TBO lists are approved by DGCA, all the
seals shall be renewed at the time of overhaul of the
components. However, the maximum service life of the seals
shall not exceed 4 years wherever such information is not
available. In case manufacturers have fixed the service
life of the components involving rubber components as less
than 4 years, the manufacturers recommendations shall be
followed. However, the TBOs of such components may be
developed limited to maximum service life of rubber
components/seals as 4 years, under a life development
programme mutually agreed by the Regional Airworthiness
Office and the aircraft operator.
Sd/-
(K. N. S. Krishnan)
Director of Airworthiness
for Director General of Civil Aviation