Cirrus SR20 User manual

CIRRUS AIRPLANE MAINTENANCE MANUAL MODEL SR20
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STANDARD PRACTICES: STRUCTURES
1. GENERAL
This Chapter contains standard practices for the maintenance and repair of composite structures for Cirrus
aircraft and components. The objective governing all recommendations in the following procedures is to
restore the composite structure to its original level of strength and durability.
The general procedure for using the Chapter 51 - Standard Practices: Structures is as follows:
The extent of damage is determined using the methods outlined in Section 10 - Investigation, which
contains guidance for identification of damage and associated classifications. (Refer to 51-10)
Processes and methods used in the repair of the aircraft are described in Section 20 - Processes.
(Refer to 51-20)
Approved materials and equipment necessary to perform standard repairs are contained in Section 30
- Materials. Prior to each repair process, a table listing all necessary tools, equipment, and supplies is
provided. (Refer to 51-30)
Section 70 - Standard Repairs contains specific composite repair procedures that are used with the
supporting processes outlined in Section 20. (Refer to 51-70)
Prior to each repair process, a table listing all necessary tools, equipment, and supplies is provided.
For information related to safety equipment refer to Section 00 - Standard Practices: Structures. (Refer
to 51-00)
A discussion on personnel qualifications, description of the primary structural components, Airframe Zone
Diagrams outlining the principal repair areas, and a definition of terms used in this Chapter are included
below.
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A. Personnel Qualifications and Safety
Repair personnel must be fully qualified in the preparation and handling of repair materials and the
repair of composite laminate construction.
The capability of a repair to satisfactorily maintain its integrity for the remaining life of the aircraft is
dependent on the quality of the repair. Therefore, it is essential that the procedures outlined in this
Chapter be carefully followed and that all repairs be conducted with the highest possible degree of
workmanship.
Materials used for the manufacture and repair of laminates are potentially dangerous. Prior to perform-
ing any repair the following Health and Safety Information, Safety Equipment, and First Aid Procedures
should be reviewed:
WARNING: The repair procedures described in this Chapter call for the use of processes and/
or substances that may be harmful to the health if adequate precautions are not
taken. Materials used for the manufacture of laminates are potentially dangerous
and may cause a number of health hazards.
(1) Health and Safety Information
(a) Materials used for the manufacture of laminates are potentially dangerous and prior to use
the material safety data sheets must be read.
(b) Damaged composite materials may cause a number of health hazards. Single fiber parti-
cles, with a diameter of 3 to 4 microns and a length of less than 0.1 mm pose the greatest
threat to the respiratory system. Respiratory protection is essential for those operations,
such as drilling and sanding where dust exists or is generated.
(c) Composite material dust is injurious to health. A respirator must be worn at all times when
drilling or sanding composite materials.
(d) Individual fiber filaments are very brittle and broken fiber may cause irritation to the skin.
Approved barrier creams should be used and protective clothing worn. If irritation is felt,
thorough washing and rinsing will remove loose filaments.
(e) Technicians should, before mixing and using the repair resin, apply liberal quantities of
approved barrier cream to their hands (particularly around the finger nails) and wrists.
(f) To keep resin from contacting the hands, rubber gloves must be used (in addition to the
barrier cream) when carrying out a repair.
(g) Resin deposits on the skin should be removed before they set hard by wiping with a clean
rag. Removal of obstinate deposits of resin and final cleaning of the hands after the repair
should be carried out by applying a quantity of white vinegar, thoroughly rubbing in, wiping
with a clean rag, and followed by washing in warm water. Resin that is allowed to set hard
on the skin cannot be removed.
(h) Acetone should not be used on the hands as it removes the natural oils from the skin and
may have other associated health hazards.
(2) Safety Equipment
(a) Respiratory Protection-Dust and Vapor Masks
Depending on the hazard presented by the material being used, appropriate masks must
be worn. When sanding, a dust mask must be worn. When masks are worn for protection
against gases or chemical vapors, ensure the correct type of mask is used. Full-face (neg-
ative pressure) masks are available and can be fitted with a wide range of filter canisters to
suit gases, solvents, or particulates against which protection is required. Always consult
the Material Safety Data Sheet for each hazard, and use the recommended protection.
(b) Eye and Ear Protection
Goggles giving all-round eye protection should be worn when drilling or sanding compos-
ite materials, and when chemicals are being used. Ear protection should be worn for noisy
processes such as grinding.

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(c) Clothing
A resin proof apron should be worn when the situation demands that level of care. If mate-
rials being used are toxic by absorption through the skin, coveralls providing complete pro-
tection may be worn.
(d) Barrier Creams
An approved barrier cream should be rubbed into the hands before commencing work with
resins and adhesives. Moisturizing creams and barrier creams protect the skin but must
be regarded only as supplements. They should be used in conjunction with gloves rather
than as a replacement for gloves. Refer to Section 30 - Materials for approved barrier
creams. (Refer to 51-30)
(3) First Aid Procedures
Refer to the products material safety data sheet for additional first aid information.
(a) Skin Contact
Immediately remove liquids from the skin by wiping with disposable towels, then cleanse
the skin with white vinegar, followed by washing with warm soapy water. Do not use sol-
vents.
(b) Eye Contamination or Irritation
Immediately flush the affected eye with eyewash bottle or fountain - or with low-pressure
running water- for at least 15 minutes. Seek medical attention promptly.
(c) Inhalation
Operators affected by the inhalation of vapor, droplets, etc., should be taken immediately
into fresh air and made to rest while medical attention is called.
(d) Clothing
Remove and isolate contaminated overalls and clothing. Launder before re-use.
(e) Ingestion
Immediately rinse the mouth repeatedly with water. If swallowing has occurred, drink
plenty of water. Seek medical attention promptly.
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B. Primary Structural Components
The airplane is constructed primarily of composite materials composed of fiberglass, carbon, epoxy
resin, and foam core. Each component uses a combination of construction methods, employing vary-
ing ply thicknesses to achieve the necessary strength for component sections with differing load
requirements. Primary structural components include: fuselage, wing, vertical stabilizer, and horizontal
stabilizer. For additional information pertaining to the structural components listed below, see the refer-
enced Chapter following each component description.
(1) Fuselage
The fuselage is a fiberglass/epoxy structure. The skins form a monocoque shell with the left and
right halves bonded together. The main section of the fuselage is reinforced by a rollcage struc-
ture that supports loads in case of a rollover. The rollover structure also contains side longerons
to support bending loads in the fuselage. In addition, the fuselage contains a floor structure and
floor longerons as well as bulkheads to add stability. Forward and aft spars as well as two ribs
support the empennage. (Refer to 53-00)
(2) Wing
The wing is a fiberglass/epoxy, bonded structure consisting of a main spar, aft shear webs, six-
teen main ribs, fourteen leading edge ribs, upper and lower skins, and two wing tips. (Refer to
57-00)
(3) Vertical Stabilizer
The vertical stabilizer consists of two C-channel spars fabricated from fiberglass/epoxy. Two ribs
are bonded to the spars and the right and left fuselage skins cover the ribs and spars to form a
two cell box beam structure that resists bending and torsion created by wind gust and aircraft
maneuvers. The vertical stabilizer is structurally bonded to the fuselage. (Refer to 55-30)
(4) Horizontal Stabilizer
The horizontal stabilizer is a fiberglass/epoxy composite assembly composed of sandwich skins
bonded to ribs and spars. The horizontal stabilizer is structurally bonded to the fuselage. (Refer
to 55-10)

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C. Construction Methods
Construction methods used in primary structural components are described below:
(1) Secondary Bond
Composed of paste adhesive, secondary bonds are used most commonly at primary structural
joints to bond previously cured composite parts together. For example, the spar-to-ribs bond
forming the torque box is a secondary bond.
(2) Solid Laminate
Composed of fiberglass and/or carbon, and epoxy, solid laminates are used where thinner con-
struction is required at lightly loaded areas, such as aft shear webs and most ribs.
(3) Sandwich Construction
Composed of fiberglass and/or carbon, and epoxy composite layers encasing closed-cell foam
core, sandwich construction stabilizes both layers to prevent buckling in more heavily loaded
areas, such as wing skins, bulkheads, floors, longerons, and ribs.
D. Metal Components - Corrosion Control
Corrosion is the deterioration of metal by chemical or electrochemical attack. Water which is allowed to
remain on the aircraft and industrial pollution are the major causes of corrosion in aircraft. The two
general types of corrosion are Direct chemical attack. (i.e. spilled battery acid) and Electrochemical
attack which requires a medium. (usually water)
(1) Forms of Corrosion
Contact Cirrus Design for disposition. (Refer to AMM-Intro-)
(2) Conditions Affecting Corrosion
Contact Cirrus Design for disposition. (Refer to AMM-Intro-)
19 Sep 2017