| by |
Kenneth A. Cubbin |
Immediately
after Air France's Concorde crash, graphic photographs and video of the
disaster were broadcast to millions of television viewers. So-called industry
experts appeared on various networks soon after and speculated about the cause
of the crash. One pundit, who has authored a book on aging aircraft, raised
the specter of the inherent danger to passengers who travel on older aircraft.
The author claimed that deregulation has caused many airlines to keep
operating aircraft past their design life.
However, initial investigative reports indicate that the Concorde tragedy
was caused by a tire blowout that pierced a fuel tank and caused damage to at
least one engine. In response, pundits are now claiming that the Concorde's
design is inherently dangerous and that this type of accident was inevitable.
One fact is clear although not reported: The accident was not a direct result
of the age of the aircraft, despite the widely reported finding of small
cracks in the wing structure of some Concordes a few days before the Paris
crash. Even so, British Airways and Air France have since grounded their
Concorde fleets indefinitely.
A
week or two before the Concorde crash, a Boeing 737-200 operated by Alliance
Air, an Indian Airlines subsidiary company, crashed at the Patna, India,
airport while executing a go-around. Reporting via telephone on CNN shortly
after the accident, Indian news representatives indicated that concern was
being raised immediately over whether the 20-year-old Boeing 737 had been kept
in service too long. According to Indian Airline's reports, the aircraft was
number 671 on the Boeing production line and had accumulated 44,087 hours and
49,500 cycles. Subsequent reports by ground observers claim that an engine may
have been on fire before the crash.
Fast-food Answers
The public is outraged at any airline accident and wants immediate answers.
If the aircraft in the accident was older than 15 or 20 years, they are all
too willing to believe claims by self-interested "experts" who say
such aircraft are increasingly at risk of falling out of the sky. In accidents
where the aircraft is relatively new, blame is immediately assigned to the
pilots and advanced technology with which they interact.
In
this "fast-food-immediate-answer" environment, the NTSB and similar
international authorities have to wade through the evidence to establish the
most probable cause of the accident. Note the two words: "probable
cause." Experts, analyzing all available data, will not conclude what
definitely caused an accident, only what the most likely cause was. And yet,
hours after any accident, media spokespersons have assigned blame by
inference.
Competing Economic Forces
It is a fact that since deregulation, competition has forced many airlines
to continue to operate aircraft past their intended service life. Indeed, one
large airline operates a significant number of older-technology aircraft with
an average age of 18 years. Even so, some carriers, such as Delta Air Lines,
intend to replace their older-technology aircraft in the near future. However,
this decision is based on the disproportionate cost of maintaining these
older-technology aircraft rather than their inherent lack of safety and
airworthiness.
Singapore
Airlines and Cathay Pacific are taking the opportunity to monopolize on the
traveling public's apprehension of older technology airplanes by overtly
advertising the newness of their fleets. These airlines' implied message is
that new aircraft are safer and more comfortable while older aircraft are less
safe and lack amenities offered by newer technology.
It would seem that in these times of marketing madness, people adopt
conceptions of industry standards based on what is presented via the media.
The problem is that most media reports sensationalize air travel safety and
most politicians and critics of older aircraft act on self interest. No one,
it seems, is interested in presenting a balanced look at this particular
problem.
Well, are aging aircraft a danger to the traveling public? Let's take a
look.
Recent U.S. Accidents Involving 20-Plus-Year-Old Aircraft
Analysts say that human error has accounted for 70 percent of aircraft
accidents over the last decade. A small portion of these are maintenance
induced; however, very few accidents have occurred as a direct consequence of
aging aircraft systems or structural integrity. There are two spectacular
accidents worth taking a close look at since they have both spawned
initiatives aimed at eliminating similar events.
TWA 800
TWA flight 800 departed John F. Kennedy International Airport in New York
on July 17, 1996, on its way to Paris and blew apart in the air a short time
later. Four years later, the NTSB investigators and Boeing are in agreement
that an explosion in the center wing fuel tank caused the accident. Despite a
$32-million study conducted by Boeing, company officials were unable to
determine the source of the spark that allegedly ignited volatile fuel vapors
in the tank.
A
preliminary report by the NTSB suggests that fuel vapors in the empty
center wing tank of the Boeing 747-100 were heated to an explosive level by
the air-conditioning packs during more than two hours of ground time.
Subsequently, during climbout, this explosive mixture was ignited by an
unknown source. The explosion is thought to have originated in one of the two
center compartments of the fuel tank and rapidly moved forward, ultimately
resulting in separation of the entire nose of the airplane from the fuselage.
In its
preliminary report, the NTSB suggested that the "most likely" source
of ignition was a "short circuit outside of the center wing tank that
allowed excessive voltage to enter it through electrical wiring associated
with the fuel quantity indication system." The board expressed the
opinion that the fuel tank design of the Boeing 747 was "fundamentally
flawed." However, the board went on to say that there are no critical
hazards in fuel tanks and wiring that require emergency action. The latter
statement concurs with a recent statement by the Air Transport Association
(ATA).
While the ignition source is yet to be determined, subsequent inspections
of other older-technology aircraft revealed some disturbing problems with fuel
tank wiring. As a result, two Airworthiness Directives requiring fuel tank
wiring inspections were issued by the FAA for Boeing 727 and Boeing 737
aircraft. And recently, the FAA has been considering a ground-based system
that would pump inert nitrogen gas into fuel tanks of commercial jetliners.
Such a system is estimated to cost approximately $1.6 billion to install. For
years, the military has pumped nitrogen into tanks of fighters and transports
in order to protect them from occasions when a bullet might ignite fuel tank
vapors.
While rare, occasional fuel tank explosions do occur. In 1990, a Boeing 737
exploded while taxiing for takeoff at Manila airport. Eight people died as a
result. The NTSB and other investigators have publicly shown their displeasure
at Boeing for not disclosing data from a study the company conducted on
military 747s in 1980 where problems with center wing fuel tank overheating
were revealed. One of the key findings of the study was that hot runways and
air-conditioning packs can overheat fuel tanks. To reduce this effect, it was
concluded that insulation should be added to shield the tanks from such heat
sources.
Sources at the NTSB reportedly said that if they had been privy to the
findings of Boeing's report at the time they were investigating the Manila
accident, a red flag might have been raised which may have led them to
recommending fuel tank changes. In its defense, Boeing agrees that it is
embarrassing the test results were overlooked, but points out that the study
was conducted on fuel pump problems in the military which are significantly
different to those used on commercial jetliners.
Responding
to public concerns over aging aircraft, the
White House Commission on Aviation Safety and Security (WHCSS) recommended
that the FAA expand its Aging Aircraft Program to also cover non-structural
systems. As a consequence, the
FAA Aging Non-Structural Systems Plan was formulated. It describes various
maintenance, training and reporting initiatives, development of advisory
material, research programs and other activities. This program will be
discussed later in this article, but for now it is worth noting that
significant deficiencies in wiring inspections of aircraft in service were
revealed. Numerous problems with aircraft wiring, such as frayed wires,
contamination from water and other substances, and the frequent presence of
metal shavings were found.
Aloha 243
In 1988, an Aloha Airlines Boeing 737 lost an 18-foot section of its
fuselage at approximately 24,000 feet due to metal fatigue. Miraculously, only
one person died — a flight attendant — and the crew was able to land the
aircraft safely.
As a
result of this accident, several well-needed studies on metal fatigue and
corrosion were initiated. What was revealed from these studies was that
corrosion is an insidious threat to structural integrity that can be almost
impossible to detect in some circumstances without non-destructive methods.
Often it is necessary to disassemble aircraft structures in order to gain
access to areas of interest. Methods commonly used to detect corrosion
include: visual inspections, radiography, ultrasonic, acoustic emission, eddy
current, magnetic particle and dye penetration.
Aluminum alloys used in aircraft structures have changed over the years,
with some being more prone to stress corrosion cracking than others. Surface
corrosion, pitting corrosion and exfoliation were found to be improved if the
alloys were clad with pure aluminum. However, this cladding is removed in
certain areas such as in countersunk rivet holes. What becomes important in
how and when corrosion will occur is the geographical location of the airport
where the aircraft is parked, material selection, surface preparation,
material removal and cleaning methods.
A multiple-site damage crack, such as occurred on Aloha 243, can be
initiated by small cracks that initiate and propagate from highly stressed
rivet locations. A sudden failure of a panel can cause several additional
panels to fail almost instantly. However, there is no known method for
determining either corrosion initiation or propagation times. As a result,
periodic inspections are the only viable method of detection. Data gathered
from inspections could be shared between operators and manufacturers to
develop a risk analysis on the ultimate safety of the aging aircraft fleet.
A combination of obliquely backscattered ultrasonic signals (OBUS) and
sensor-array real-time imaging (SARTI) promises to reduce the need to remove
paint from aircraft surfaces prior to inspection. These nondestructive methods
for detecting flaws in aircraft structures could help ensure that aging
aircraft remain structurally sound while holding down maintenance costs.
The goal of iterative testing and analysis is to determine the ultimate
economic life of the aircraft. At some point, the maintenance costs become
prohibitive and the airplane is replaced. Now, however, there is the added
marketing aspect of the traveling public's concern over aging aircraft to be
factored into the equation.
Queen Of The Skies
The TWA and Aloha Airlines accidents can actually be linked to probable
failures due to the age of the aircraft. In the first instance, decayed wiring
in the fuel tank, and in the second, metal fatigue caused by undetected and
treated corrosion. But not all older-technology aircraft are being put out to
pasture. The inveterate DC-8 is still flying proudly and promises to be the
first jet airplane to be operated commercially for 40 years.
The
DC-8 was the first jet-powered transport manufactured by the Douglas Aircraft
Company and entered service with United Airlines and Delta Air Lines in 1959.
There are series -10, -30, -40, -50, -60, -61, -62, -63, and -70 models of the
four-engine transport; the latest modification being the incorporation of
high-bypass turbofan engines. Out of a total of 556 aircraft being built over
a 14-year production run, approximately 300 DC-8s are still in service today.
DC-8s provide the backbone of many cargo fleets, such as Emery Worldwide and
Airborne Express.
In the last 10 years, there have been seven DC-8 crashes in the U.S., none
of which can be attributed to aging aircraft structure or systems. The
latest accident occurred in February of this year when an Emery Worldwide
Cargo DC-8 crashed shortly after takeoff from Sacramento. Although the
cause of this accident has not been determined, the last communication from
the aircraft allegedly implied that the crew was experiencing a severe center
of gravity problem. The other six accidents are:
-
A
Fine Air DC-8-61F that crashed after takeoff from Miami, Fla., in 1997;
the NTSB found the probable cause to be severe center of gravity problems.
-
An
Airborne Express DC-8-63 that crashed in Virginia during flight tests in
1996; the NTSB found the probable cause to be inappropriate control
inputs being applied during a stall recovery attempt.
-
An
Air Transport International (ATI) DC-8-63F that crashed after takeoff from
Kansas City, Mo., in 1995 while attempting a three-engine ferry flight.
The NTSB found that the captain probably rotated too early resulting in a
stall.
-
A
Kalitta International DC-8-61 that crashed on approach to Guantanamo Bay,
Cuba, in 1993; the NTSB found contributory factors of impaired
judgment, decision-making and flying abilities of the captain and
flightcrew due to fatigue, coupled with the Navy's failure to provide a
system that would assure the local tower controller was aware of the
inoperative strobe light.
-
An
Air Transport International DC-8-63F, that crashed on approach to Toledo,
Ohio, in 1992; the most probable cause was found to be spatial
disorientation of the captain and failure of the crew to recognize or
recover from the unusual aircraft attitude in a timely manner.
-
An
Air Transport International DC-8-62H-AF that overran the runway after
aborting the takeoff from JFK in 1991; the flight engineer had
allegedly calculated V-speeds and trim settings for 242,000 lbs when the
actual takeoff weight was 342,000 lbs.
What is immediately evident from these accidents (with the possible
exception of the three-engine ferry case) is that the structural integrity and
system operation of the aircraft were sound. Since all the DC-8s involved in
the accidents were more than 20 years old, this is pretty convincing evidence
that age alone is not an exceptional risk element in airline operations. It
also reinforces the fact that human error accounts for most accidents.
Wired For The Twenty-first Century
In compliance with the FAA's
Aging Non-Structural Systems Plan, the FAA, in cooperation with airlines
and manufacturers, has initiated steps that include full and complete
teardowns of selected aircraft due to go out of service. There are also steps
to establish a lead-the-fleet research program, an expansion of the
FAA-DOT-NASA cooperative aging aircraft program, an expansion of programs of
the Airworthiness Assurance Working Group to include non-structural
components, and encouraging the use of modern technical know-how to predict
ongoing airworthiness of aging non-structural components and systems.
Usual
procedures for monitoring non-structural systems are addressed through the
FAA's continuing airworthiness program. Airplanes are routinely maintained,
inspected and repaired as necessary; as the aircraft becomes progressively
older it becomes more expensive to maintain its airworthiness and reliability.
At this point, depending on the economic status of the airline and industry,
the airplane is usually replaced.
As part of the study, specialist engineers visited airline maintenance
facilities to visually inspect three DC-10s, one DC-9 and a B-727 undergoing
heavy maintenance checks. These aircraft were chosen based on their
availability, age, hours of operation and cycles. Systems primarily of
interest included wiring, lightning protection, hydraulics and flight control
systems.
The investigators found some areas of serious wiring deterioration, damage
and contamination. Deterioration was found in wiring bundles, connectors,
grounds, clamps and shielding. Wire insulation becomes stiff and easily
cracked if improperly handled or allowed to move unrestrained and the
investigators found some evidence of isolated cracking of outer layers in
multi-layer insulation wire types. Contamination of wiring bundles by metal
shavings was evident and this was presumed to have occurred during previous
maintenance. Heavy dust and various fluid contaminations were also evident in
some areas. Ground terminals were found to have resistance measurements
outside manufacturer's specifications and isolated cases of connector pin
corrosion were revealed.
A principal area of concern revealed by these inspections is the inadequacy
of current wiring inspection methods. Inspection criteria are too general and
usually require that only a visual inspection be performed. One example of
these inadequacies is that under current maintenance philosophy, wiring inside
conduits is not inspected. It has generally been accepted that this wiring is
protected from damage. While these inspections were conducted on aircraft
using primarily mechanical or hydraulic fight control systems, the
investigators expressed particular concern over the implications for
fly-by-wire airplanes. These airplanes, some of which have been in service for
fifteen years, have full-authority electronic flight and control systems. The
ramifications of wiring faults on this category of aircraft are potentially
more catastrophic than older technology airplanes.
Conclusion
It
is possible that one operator might figuratively run an aircraft into the
ground where another will perform regular maintenance in a conscientious
manner. It is also true that accidents rarely occur due to one factor alone:
There is usually a chain of events that lead to a catastrophe. In some
accidents, aging aircraft systems might have played a contributory role.
However, system abnormalities also affect newer technology airplanes. One case
in point is the Swissair MD-11 accident where faulty wiring in the cabin
entertainment system has allegedly been cited by some investigators as a
possible source of the fire that ultimately disabled the crew.
What is blatantly apparent is that an airline's maintenance philosophy is
reflected by its on-time departures and arrivals, canceled flights and
diversions.
When
an airline's management team decides to increase its competitiveness by
curbing maintenance costs, reducing training or stretching existing staff
expertise to its limits, they are practicing false economy. One prime example
of this may be the recent spate of incidents incurred by Qantas, the erstwhile
premier airline for safety. Qantas has experienced an embarrassing array of
incidents, including a BAE-146 packed with politicians that suffered an engine
failure during takeoff, a B-747-400 that
overshot the runway at Bangkok, a B-747-200 that lost a piece of an engine
during flight and a B-747-300 that had its undercarriage collapse while
preparing to take off from Rome. Qantas' unions allege that cost-cutting has
led to lapses in maintenance standards. It could be bad luck, but to me the
unions seem to be spot on the money.
Some aircraft accidents have occurred due to basic design flaws that were
grandfathered into new models. Some pundits allege that the B-737 rudder
system stands as a good example. It is possible that the B-747 center fuel
tank system may be another. However, design flaws are only evident over time.
The important thing is that these flaws be addressed on an aggressive basis.
Boeing has agreed with the FAA that a ground-based system to pump inert gases
into fuel tanks may be viable. In the meantime, I for one will be asking for
ground air-conditioning carts to be connected during turnarounds so it won't
be necessary to run the packs for long periods of time.
As revealed in this article, corrosion, metal fatigue and wiring problems
can be addressed by aggressive maintenance procedures. Whether this is
economically better than investing in new equipment is for airline management
teams to decide. However, clearly the FAA must oversee airlines to ensure that
maintenance procedures are not circumvented in the drive for profits. What we
don't need are the "buy-my-book" authors, and
"elect-me-next-term" politicians who are only too eager to scare the
traveling public for personal gains.
If
I had to estimate the statistical probability of an accident occurring solely
because of an aircraft's age — that is, events similar to TWA 800 and Aloha
243 — I would say the odds are better than 1 in 100 million. But that is just
a guess. However, I would like to know why people don't ask what the odds are
of a two-engine failure on a B-777 now that ETOPS limits have been stretched
to 204 minutes? Is it because there aren't any political gains to be had? Or
is it just that we haven't experienced any instances of this calamity yet?
We'll see. It hasn't happened yet, but believe me, it will. How do I know?
Simply because it can happen. And when it does, stand back! The traveling
public is going to want heads to roll. Until that time, whether you are
traveling on older-technology airplanes or state-of-the-art, new-technology
wonders, remember that it is the human element in the operation of the
airplane that is the most crucial factor. When it comes to pilots, most
passengers would agree that a little gray in the hair is a good thing.
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