Bell OH-58A - Chapter 4: Airframe; Section I. Introduction

TM 55-1520-228-BD
CHAPTER 4
AIRFRAME
BDAR FIXES SHALL BE USED ONLY IN COMBAT OR FOR TRAINING
AT THE DISCRETION OF THE COMMANDER.
(AUTHORIZED TRAINING FIXES ARE LISTED IN APPENDIX E.)
IN EITHER CASE, DAMAGES SHALL BE REPAIRED BY STANDARD
PROCEDURES AS SOON AS PRACTICABLE.
Section I. INTRODUCTION
4-1. SCOPE. This chapter contains
information on battle damage assess-
ment and expedient repair procedures
for the OH-58 helicopter airframe.
The procedures are to be used only
during combat operations or during
periods of extreme emergency.
a. Section I contains information
pertaining to the various structural
areas which are suspected of being
damaged, and whether the damage is to a
primary or secondary element. Logic
flow chart tables and damage limit
tables are also part of this section.
b. Section II consists of expedient
structural repairs and procedures on
how to perform these repairs and field
fixes.
4-2. ASSESSMENT PROCEDURES. Refer to
Table 4-1.
4-3. GENERAL. Aircraft structure is
classified as primary and secondary
structure.
a. The primary structure is the basic
structure which holds the aircraft
together.
Any serious damage to any
element of the primary structure will
restrict the combat capability of the
aircraft. The primary structure for
each major airframe subassembly is
shown in Figure 4-11, Sheets 1 thru 5.
b. Secondary structures are mounted
on the primary structure.
No amount
of structural damage to secondary struc-
tures will restrict combat capability
from a structural point of view;
however, secondary structure may be
required for aerodynamic reasons or to
accomplish or support mission functions.
4-4. STRUCTURAL DAMAGE ASSESSMENT AND
REPAIR.
The battlefield structural
damage assessment and repair consists of
three steps:
an initial assessment,
paragraph 4-5; a detail assessment,
paragraph 4-6; and a repair plan,
paragraph 4-10.
The initial assessment
is a quick visual assessment to decide
whether or not a detail assessment
should be made.
A detail assessment
involves the identification of all
damage to primary structural elements,
possibly some clean-up and measurement
of the damage and of the damaged ele-
ments. The procedure is described for
various aircraft sections in this
chapter. This process requires damage
measurement and determination of the
corresponding damage limits.
The repair
plan is based on an analysis of the
detail assessment.
An overall view of
all the aircraft zones is shown in
Figure 4-1.
4-5. INITIAL ASSESSMENT. To perform an
initial assessment, the assessor must be
acquainted with structural damage modes
and the primary structure as shown in
the figures of this chapter. He shall
be capable of differentiating between
primary and secondary structure, and he
must understand the function of primary
structural elements.
The initial assess-
ment consists of a visual inspection of
primary structure. The assessor deter-
mines if any primary caps, webs, or
panels are damaged or fractured and
decides whether:
4-1