introduction: managing ageing aircrafts
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Introduction Chapter
An aging aircraft, commonly, is defined as an aircraft that has already operated more than 75% of its
designed flight hours. But the CAAC, gave the definition of an aging aircraft as an aircraft that has beenused for more than 14 years is to be considered as an aging aircraft. [1]
Aircraft today typically are expected to last longer than automobiles. This is due to many factors,
including the cost of the aircraft, government regulations, and the dramatic consequences of failure. [2]
The world fleet averages 11.7 years old aircrafts, the U.S. fleet 12.7, and the most elderly commercial
aircraft are over 24. This situation is arising because the carriers have been nickel-and-diming
maintenance budgets. Patrick Murphy, chief operating officer of Avitas Inc., a Reston, Virginia, firm that
does maintenance audits for 80 airlines worldwide, thinks more spending is needed: ''All the money that
U.S. carriers cut from maintenance is going to come back and bite them. However, safety takes more
than replacing an old aging aircraft. A brand-new jet, poorly maintained, can crash tomorrow. [3]
The case of Aloha Airline Flight 243 may be just seen as one of the best examples but with the
considerable growth of commercial aviation in such a short period of time sufficient number of aircrafts
have been kept in operation and significant numbers are now operating beyond their initial design lives.
These trends have focused the attention of both airworthiness authorities and aircraft manufacturers
and repairers the need to acquire improved understanding of the behaviour of ageing aircraft
structures. [4] The aircrafts operate in an environment that is corrosive and it can lead to different
corrosive failures such as pitting and exfoliation. Corrosion-nucleated fatigue can result in serious and
fatal aircraft joint failures, which are already prime locations for fatigue, because of high density of holes
and high stress concentrations in these areas, disastrous circumstances can develop for an aircraft that
is already aging and has number of flight cycles. [5]
It is therefore, necessary to track the usage of every individual aircraft, since all aircrafts are not
operating in the same environments and loads experienced by every aircraft may significantly vary from
another aircraft of same build but operating in different operational environment. Nevertheless,
whether it is a newly acquired aircraft or an aging fleet aircraft the structural life ceiling limits of the
fleet aircraft are defined from three distinct approaches: safe-life, fail-safe and damage tolerant
approaches. [6] A process flow chart influencing the structural life of an aircraft is given below:
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The above shown diagram is taken from (IYYER, N; et al.)
The key factor in order to ensure that the aircraft is safe to operate is well maintenance. There is an
essential requirement of an authority in the aviation industry that makes use of the cost-effective SHM(Structural Health Monitoring) equipments, and monitors the structural fatigue and corrosion
management of the commercial aviation aircrafts through collaborative research with the academia and
the industry. At present, in Australia, neither the aircraft users nor any regulatory authority has adopted
the use of a Structural Health Monitoring of aircrafts systems .And it is noted that the on-board SHMs
that are in use are not capable of monitoring the structural fatigue and monitoring of the aircraft. [7].
Although, now, steps are being taken by the industry in order to improve the maintenance procedures
of aircrafts and the maintenance requirements of aging aircrafts are quite stringent now. But in order to
bring the aircraft maintenance and fleet management to a new level, there is still a lot of room for
improvement.
Inspiration can be taken from a recent study conducted by Boeing Australia’s Aging aircraft managementprogram. The program was initiated in 2001 and was a proactive approach to be able to maintain, fly
and sustain an already aging fleet safely and cost-effectively. The program focuses on sustaining a fleet
of old age military platforms such as F-117 and B-707 and identifying the effects of aging the fleet and
integrating new technologies that come along with time in the same platforms. [8]While this program is
solely based on military planes, commercial aviation should observe the results of this program and
apply a similar approach to their General Aviation aircrafts.
Also there is another model being used by the RAAF (Royal Australian Air Force) which has a system in
place for transitioning the structural integrity of an aircraft fleet from safe life to safety by inspection.
This helps in maintaining a fleet that initially was certified and managed by a safe-life standards, but as
its flight cycles increase the aircraft is gradually transitioned to safety by inspection (SBI) management tomaximise the service life of the aircraft. The reference standards used by the RAAF is the DEFSTAAN 00-
970 [9] of the RAF (Royal Air Force). There are now a number of aircrafts within the RAAF that were
certified to a safe-life but have now been transitioned to either full or partial safety by inspection model.
[10]. This is another model that commercial industry can look into and apply similar techniques to the
commercial aircrafts in order to safely extend the service life of a General Aviation aircraft.
The challenge of keeping aircraft fleets in service for long periods of time significant effort to maintain
acceptable levels of safety under the constraints of resources and demands of capability. [11] Failure of
an aircraft component can have disastrous consequences with loss of life and aircraft. It is therefore
necessary that investigation of defects in aircrafts is identified, studied and prevented in order to
prevent further loss of life. [12]
The purpose of this study is to highlight the importance of further study required to study and develop
new methods for aging aircraft fleet maintenance management plan, since there are more and more
aging aircrafts being operated within the industry due to financial and budget constraints of smaller
aircraft operators, and how this could lead to compromising the safety of the aircraft and people on
board. The fundamental research question that this paper is aiming to answer is:
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“ Aging aircraft. Is it an unacceptable risk?”
References:
1. YONGGANG, W; HONGLANG, L. Summary and Analysis of the Aging Aircrafts’ Failure. Procedia
Engineering. 17, The 2nd International Symposium on Aircraft Airworthiness, 303-309, Jan. 1,
2011. ISSN: 1877-7058
2.
Hill, E. K., & Rovik, C. L. (2013). In-Flight Fatigue Crack Growth Monitoring in a Cessna T-303
Crusader Vertical Tail. Journal of Acoustic Emission, 31(1), 19-35.
3.
RAMIREZ, A; RILEY, I. HOW SAFE ARE YOU IN THE AIR? Terrorists and an aging fleet of aircraft
threaten the industry's impressive safety record. Maintaining safety in the air and security on
the ground will get costly. Fortune. 119, 11, 75, May 22, 1989. ISSN: 00158259.
4.
HORST, P; TREY, H. Structural maintenance of ageing aircraft: SMAAC. Air & Space Europe. 1, 71-
74, Jan. 1, 1999. ISSN: 1290-0958
5.
JAYA, A; TIONG, UH; CLARK, G. The interaction between corrosion management and structural
integrity of aging aircraft. Fatigue & Fracture of Engineering Materials & Structures. 35, 1, 64-73,
Jan. 2012. ISSN: 8756758X.
6.
IYYER, N; et al. Aircraft life management using crack initiation and crack growth models – P-3C
Aircraft experience. International Journal of Fatigue. 29, 9-11, 1584-1607, Sept. 2007. ISSN:
01421123
7.
KOUROUSIS, KI. A holistic approach to general aviation aircraft structural failure prevention in
Australia. Aviation (1648-7788). 17, 3, 98-103, Sept. 2013. ISSN: 16487788
8.
Gauntlett, Richard. Integrating an Ageing Aircraft Program into the Running System [online]. In:Australian Aeronautical Conference (12th : 2007 : Melbourne, Vic.). Twelfth Australian
Aeronautical Conference. Melbourne: Engineers Australia, 2007: [113]-[126]. Availability:
ISBN:
9780980321500.
9.
United Kingdom Ministry of Defence, Design and Airworthiness Requirements for Service
Aircraft, DEFSTAN 00-970, Part 1 – Combat Aircraft, Issue 5, 31 January 2007.
10.
Watters, K, & Livingstone, P 2011, 'Risk analysis of safety by inspection of ageing aircraft',
AIAC14: Fourteenth Australian Aeronautical Conference, p. 671
11.
BOYKETT, R; GOODWIN, A. Ageing aircraft systems audit - fighting the ageing process. AIAC14:
Fourteenth Australian Aeronautical Conference. 692, 2011. ISSN: 9780987086303
12.
FINDLAY, S; HARRISON, N. Review: Why aircraft fail. Materials Today. 5, 18-25, Nov. 1, 2002.
ISSN: 1369-7021.