1. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
WEEK 4:
THE CONCEPT AND PRINCIPLES OF HELICOPTER
MAINTENANCE
SABRI OMAR

2. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
LEARNING OBJECTIVE & OUTCOME
OBJECTIVE:
1. GAIN KNOWLEDGE ON CONCEPT AND PRINCIPLE
OF HELICOPTER MAINTENANCE ACTIVITIES.
OUTCOME:
1. DESCRIBE WHAT IT MEANS BY HARD TIME,
CONDITION AND CONDITION MONITORING.
Allen Peter Diman

3. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
DEFINITIONS OF HELICOPTER MAINTENANCE
The aircraft is delivered to the
airlines along with the Approved
Maintenance Schedule.
Deterioration of the aircraft due to
use and time factor cannot be
avoided.
If it is allowed to remain
unchecked, will lead to non-
conformity of its Type Certificate
conditions.
Or it may even lead to hazardous
as well as a catastrophic event.
Maintenance activities rectify
these conditions and restore the
aircraft airworthiness.
Maintenance is the actions
necessary to sustain and restore
the airworthiness of aircraft, its
engines and equipment.
Primary maintenance activities are
1. Inspection
2. Overhaul
3. Repair
4. Replacement
5. Modification
of aircraft, its engines and
equipment to ensure conformity
with the aircraft’s type certificate.
Allen Peter Diman

4. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Maintenance Program Evolution process
Allen Peter Diman

5. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
The objective of maintenance
program evolution is to maintain
safety, reliability, at minimum
cost. The main means to achieve
this is to adjust the initial/current
selected intervals. Such exercise is
launched when the A/C
manufacturer and the ISC
consider that sufficient in-service
experience is collected, supported
by the MRB as advisor.
Airlines report in-service
experience in the form of “Nil
findings/details of findings”
reports for each task. Then all
tasks are reviewed individually in
MWG meetings.
Allen Peter Diman

6. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
MAINTANENCE PROCESSES
Maintenance programs and
processes control the maintenance
activities of the operator and its
fleet of helicopters
There are three primary
maintenance processes:
1. Hard time
2. On condition
3. Condition Monitoring
• Hard Time and On-Condition
both involve actions directly
concerned with preventing
failure, whereas Condition
Monitoring does not.
However the Condition
Monitoring process is such that
any need for subsequent
preventative actions would be
generated from the process.
Allen Peter Diman

7. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Hard Time
This is a life-based concept.
Oldest maintenance process.
Rooted in the assumption that
reliability decreases with
increased operating age.
Its intended purpose is to prevent
failure.
This is a preventative process in
which known deterioration of an
Item is limited to an acceptable
level by the maintenance actions,
which are carried out at periods
related to time in service.
Hard time applies a fixed time
and/or cycles (e.g. calendar time,
number of cycles, number of
landings) that an item is permitted
to operate on an airplane. Upon
reaching the limit it must be
overhauled or replaced
(discarded). This includes:
1. Simple items subject to only one
failure mode
2. Components or assemblies
which have definite life limits
(for example, metal fatigue) or
whose failure could have a direct
adverse effect upon safety if they
malfunctioned in flight
Allen Peter Diman

8. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Hard Time
Components
The prescribed actions normally
include Servicing and such other
actions as Overhaul, Partial
Overhaul, replacement in
accordance with instructions in
the relevant manuals, so that the
Item concerned (e.g. system,
component, portion of structure)
is either replaced or restored to
such a condition that it can be
released for service for a further
specified period
Allen Peter Diman

9. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
The general application of the
hard time process became
outmoded as the industry matured
and aircraft became more
complex. A methodology evolved
that is oriented toward mechanical
performance, Reliability-Centered
Maintenance (RCM).
This is an analytically based
concept designed to realize the
inherent reliability of a design.
It accepts that the operation of a
component or system may fail
between required inspections, and
that the airplane may be safely
operated until the next inspection
reveals the failure.
Its application is, therefore,
limited to items whose failure
during airplane operation will not
have catastrophic consequences.
RCM uses two dominant
processes.
Allen Peter Diman
Reliability-centered maintenance (RCM) processes
On condition Condition monitoring

10. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
On condition
This also is a preventative process
but one in which the Item is
inspected or tested, at specified
periods, to an appropriate
standard in order to determine
whether it can continue in service
(such an inspection or test may
reveal a need for servicing
actions).
The fundamental purpose of On-
Condition is to remove an Item
before its failure in service. It is
not a philosophy of 'fit until
failure' or 'fit and forget it.
On condition avoids predicting
hard time failure wear-out points.
Rather, repetitive inspections or
tests that detect potential failures
are adopted.
These tests call for the removal or
repair of individual components
"on the condition" that they do not
meet a defined standard of
performance.
Allen Peter Diman

11. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
A determination of continued
airworthiness may be made by
visual inspection, measurements,
tests, or other means without a
teardown inspection or overhaul.
The checks are performed within
the time limitations prescribed for
the inspection or check.
Performance tolerances and wear
or deterioration limits are defined
in the Approved Maintenance
Schedule.
On-condition maintenance can
involve bench tests and is thus not
restricted to on-wing inspections.
However, on-wing
inspections/tests are preferred.
On condition considers specific
failure modes. It is based on the
likelihood of defining some
physical evidence of reduced
resistance to the failure mode in
question. Until that evidence is
present, units remain in service.
Allen Peter Diman
On Condition

12. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Examples of
Items under
On Condition
Allen Peter Diman

13. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Condition Monitoring
This is not a preventative process,
having neither Hard Time nor On-
Condition elements, but one in
which information on Items
gained from operational
experience is collected, analyzed
and interpreted on a continuing
basis as a means of implementing
corrective procedures.
The process applies to items that
show deterioration over time.
It consists of observing
deterioration of a component or
system as it trends toward failure.
Explicit operating parameters of
the device, which are indicative of
deterioration or wear, are selected.
Collecting and interpreting these
data “monitors the condition" of
the device.
Allen Peter Diman

14. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
This form of condition monitoring
is best exemplified by engine
condition monitoring. Parameters
such as altitude, Mach number,
inlet pressure and temperature, N1
and N2, burner pressure, and EGT
are collected.
These gas path data are
normalized and plotted against
time. They are compared against
known specific deterioration
pattern failure modes evidenced
by these parameters. These are
coupled with oil sample and
vibration analyses.
Allen Peter Diman
Accurate identification of incipient
failures is thus possible, thereby
allowing economical repair before the
occurrence of extensive costly damage;
it is most beneficial with high-cost items
such as engine components. Removal,
disassembly, or inspection is not
required.

15. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Allen Peter Diman
Honeywell Health and Usage Monitoring System

16. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Maintenance Program
The maintenance program is
developed concurrently
during type certification.
The parent document that
results is the Maintenance
Planning Document (MPD).
There are two primary
methods in which the
maintenance program is
developed.
They are
1. Hard Time methodology
for pre1980 certified
aircraft
2. MSG-3 Condition
Monitored Maintenance for
post 1980 certified aircraft
 This philosophy was
however initially only
applied to airliners such as
Boeing 747. Helicopter
comes much later
Allen Peter Diman

17. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Hard Time Methodology
The manufacturer will analytically
determine the maintenance
processes required by each
aircraft parts, components and
engine. The basis of
determination will be summed up
as follows:
Hard time items are:
1. Where the failure of the Item has
a direct adverse effect on
airworthiness and where
evidence indicates that the Item
is subject to wear or
deterioration.
2. Where there is a 'hidden
function' i.e. components that
does not give any cockpit
indications of its operational
status; which cannot be checked
with the Item in-situ.
3. Where wear or deterioration
exists to such an extent as to
make a time limit economically
desirable.
4. Where component condition or
'life' progression sampling is
practiced.
5. Where limitations are prescribed
in a Manufacturer's Warranty.
Allen Peter Diman

18. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
On-Condition items are:
1. Where an inspection, or test of
an Item to a prescribed standard
(frequently in-situ) will
determine the extent of
deterioration, and hence the
'condition', i.e. any reduction in
failure resistance.
Condition Monitoring items are:
1. Where a failure of an Item does
not have a direct adverse effect
on operating safety, and where
Hard Time and On-Condition
processes are not prescribed and
no adverse age reliability
relationship has been identified
as the result of analysis of the
data arising from a formalized
monitoring procedure or
program.
Allen Peter Diman

19. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Condition Monitored Maintenance (MSG-3)
Condition Monitored
Maintenance, as a program,
is the formalized application
of the maintenance
processes Hard Time, On-
Condition and Condition
Monitoring to specific items
as prescribed in the
Approved Maintenance
Schedule.
The controlling activity of
Condition Monitored
Maintenance is Condition
Monitoring irrespective of
whether Condition
Monitoring is prescribed as
a primary maintenance
process in the Approved
Maintenance Schedule or
not.
Allen Peter Diman

20. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Condition Monitoring is
repetitive and continuous,
the key factor in its use
being the introduction of
aircraft embodying failure
tolerant designs, which
allow for replacement of
some traditional failure
preventative maintenance
techniques by non-
preventative techniques.
Condition Monitoring is not
a relaxation of maintenance
standards or of
airworthiness control; it is,
in fact, more demanding of
both management and
engineering capabilities than
the traditional preventative
maintenance approaches.
Each Condition Monitored
Maintenance Program is
required to be approved by
the Airworthiness
Authorities.
Allen Peter Diman

21. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
SCHEDULED MAINTENANCE PROGRAMME (MSG-3)
The Hard Time
methodology is very
expensive and did not
significantly improve
maintenance. Consequently,
Condition Monitored
Maintenance is currently
preferred. Standards adopted
are formally known as
MSG-3.
MSG-3 currently includes
three revisions, the most
recent adopted in 1993.
Airplanes certificated during
the 1980s and 1990s use
MSG-3 for the development
of scheduled maintenance
tasks. MSG-3 is dominantly
task oriented rather than
process oriented.
Allen Peter Diman

22. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
MRB PROCESS
EASA and FAA require the A/C Type Certificate holder to
prepare and revise the initial minimum scheduled maintenance
requirements that are applicable to a dedicated aircraft
(Regulatory Requirement CS/FAR 25.1529). This document is
called the Maintenance Review Board Report (MRBR), and
provides the scheduled maintenance tasks and their
frequencies (intervals) for the aircraft systems (including
engine), structure and zones. MRBR development is based on
the MSG-3 method.
Allen Peter Diman

23. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Allen Peter Diman
Maintenance Review Board Process

24. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Objectives
The objectives of scheduled
maintenance are to
1. Ensure safety and
reliability of aircraft
2. Restore safety and
reliability that was lost by
deterioration
3. obtain sufficient necessary
to improve items with
inadequate target reliability
4. Accomplish these goals at
minimum costs including
maintenance and costs of
resulting failure
Allen Peter Diman

25. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Bell engineers were involved from the
start and were able to steer the
direction of the design. From the
routing of systems to the placement
and size of maintenance panels, this
group has helped develop an aircraft
that is more efficient and easier to
maintain. One result is that all of the
429’s systems are routed outside of the
cabin, either above the roof beams or
below the floor structure. The interior
of the 429 does not need to be removed
during an annual inspection and that
cuts time and cost.
Allen Peter Diman
The 429 is the first, and, so far, the
only helicopter designed using the
Maintenance Steering Group 3 (MSG-
3) process that has been the foundation
of airliner reliability since 1970. Using
this process, lead mechanics from the
customers, representatives of
Transport Canada, the FAA and
EASA, and

26. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Benefits of implementing MSG - 3
1. Maximizes aircraft availability
• Major Tenet of Aircraft Availability Improvement Plan (AAIP)
• Extended inspection intervals frees up assets
2. Safeguards inherent safety and reliability
3. Ensures Operational Safety, Suitability, & Effectiveness
4. Reduces Costs / Cost Avoidance
5. Creates program credibility and instills confidence by involving all
stakeholders
6. Integrates all levels of maintenance activity
7. Outcome has logic that is defensible at all levels of scrutiny
8. Assures that all areas of the aircraft are thoroughly covered and have the
proper level of inspection
Allen Peter Diman

27. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
Classification
of Helicopter
Maintenance
Hard Time On Condition
Condition
Monitoring
HOW MAINTENANCE ON HELICOPTER IS BEING CLASSIFIED
Allen Peter Diman

28. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
TYPES OF MAINTENANCE ON HELICOPTER
SCHEDULED
MAINTENANCE
MINOR
MAINTENANCE
MAJOR
MAINTENANCE
UNSCHEDULED
MAINTENANCE
HELICOPTER
INCIDENTS
MANUFACTURER
& REGULATORY
REQUIREMENTS
Allen Peter Diman

29. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
MINOR
MAINTENANCE
SCHEDULED
MAINTENANCE
HOURLY (25
HOURS)
CALENDAR (1
MONTH)
DAILY
MAINTENANCE
PRE-
FLIGHT/TURN
AROUND/POST
FLIGHT
Allen Peter Diman

30. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
MAJOR
INSPECTION
HOURLY
BASED
1000 HOURS
1000
HOURS/4
YEARS
CALENDAR
12 YEARS
INSPECTION
Allen Peter Diman

31. FOR TRAINING PURPOSE ONLY
Malaysian Institute of Aviation Technology
HELICOPTER
INCIDENTS
HEAVY
LANDINGS
MGB/ENGINES
CHIP LIGHT “ON”
MANUFACTURER
OR REGULATORY
REQUIREMENTS
SERVICE
BULLETINS
AIRWORTHINESS
DIRECTIVES
Allen Peter Diman