Who is really fixing our planes

NASA's Airframe Structural Integrity Program is focused on developing advanced integrated technologies to economically inspect for damage and to analytically predict the residual strength of older airplanes.

Together these programs form the technological basis for a cooperative effort with U. MSD is a form of widespread fatigue damage that is characterized by small cracks emanating from structural details such as fastener holes Sampath, If cracks emanate from adjacent fastener holes, they have the potential to link up and lead to unexpected catastrophic failures as described in the previous section.

Also, even without link-up, multiple-site cracks can severely degrade the capability of the structure to withstand major damage from other discrete sources as is described later in this section. In the past, the standard industry practice was to visually inspect the airframe for damage.

Various levels of inspections ranging from daily walk-around inspections to detailed tear-down inspections were performed. Instrumented nondestructive evaluation NDE methods such as eddy current probes were used only to inspect local regions of the structure where previous cracking problems had occurred. While these inspection methods were labor intensive and highly subjective, they were acceptable because the airframe was designed to survive a two-bay skin crack with a severed frame or stiffener.

This design criterion was established to enable the airplane to tolerate major discrete source damage i. Such damage is large enough that it should be easily detected, and the operator does not need to search for small cracks to ensure the structural integrity of the airframe.

However, this "fail-safe" philosophy assumed that the structure adjacent to the major damage e. Design residual strength requirements were based on this assumption. However, the existence of very small cracks e. Therefore, inspection of aging aircraft has become much more onerous than for newer aircraft because safety is vitally dependent on the detection of the very small cracks associated with this onset of MSD.

This represents a major challenge to the inspection and aircraft industries. The principal technical needs are 1 to develop and verify advanced NDE technology that can reliably and economically detect disbonds, small MSD fatigue cracks, and corrosion and characterize their effect on the residual strength; and 2 to develop and verify advanced fracture mechanics and structural analysis methodology to predict fatigue crack growth and residual strength of airframe structures to determine in-service inspection thresholds and repeat intervals, quantitatively evaluate inspection findings, and design and certify structural repairs.

NDE methods related to MSD are described in chapter 8 , and fracture mechanics and structural analysis methods are described in chapter 6.

Corrosion of aging aircraft has been described as an insidious problem Marceau, While other aging mechanisms, such as wear and fatigue, are somewhat predictable and can be addressed by the airline maintenance programs to preclude major structural problems, corrosion—especially in its localized forms—is very difficult to predict and detect.

Factors that influence the extent of corrosion on aircraft are materials selection, design, component processing and finishing, operational environments, and maintenance programs. It is anticipated that airplanes manufactured today will experience fewer corrosion problems than those in the current aged fleet because of significant design and corrosion protection improvements that have been implemented and because of operators' increased awareness of the role of these improvements in preventive maintenance.

Clearly, maintenance. Some examples of design improvements to reduce corrosion on the Boeing Marceau, include:. Major airline fleets include aircraft ranging in age from new to 25 years old. Consequently, the degree of corrosion protection incorporated into the airplane varies from limited protection for older aircraft to fairly extensive protection for newer aircraft. Corrosion control programs are tailored to individual fleets, depending on age, prior experience, flight environment and degrees of corrosion protection incorporated prior to the delivery of the aircraft DeRosa, All protective finishes are maintained and corrosion prevention compounds are applied during periodic maintenance.

Critical areas that are prone to excessive corrosion include areas below the galleys, doorways, lavatories, cargo compartment subfloors, inside external fairings, and the bilges which are all treated at four-year intervals. Landing gear wheel wells and wing spars are treated yearly. Longer intervals of time are allowed between reapplications of corrosion prevention compounds in the case of less-severe environments. Aging aircraft repairs have typically involved upper-skin lap fastener replacement, nonbonded skin panel replacement, skin lap doubler repairs, frame reinforcement, entryway door and scuff-plate doublers, replacement bushings and clevis joints, bulkhead forging replacement, and selected landing gear component replacement.

Based on service experience, the airlines have expectations that manufacturers of new aircraft will DeRosa, :. The objective of aging aircraft programs is to ensure the continued airworthiness of large transport aircraft as long as they remain in commercial service Curtis and Lewis, Because new materials and fabrication processes may yield different degradation and damage mechanisms, a preproduction review should ensure that the new aircraft design includes lessons learned from the existing aging fleet.

Many of the steps needed to improve aging performance are detailed below. Most of these steps have now been incorporated into recent aircraft designs. The susceptibility of aircraft to corrosion and MSD fatigue can be reduced by the following steps:. The present focus on aging aircraft will lead to better corrosion-resistant treatments for next-generation aircraft. Materials selection in wet areas, the design drainage schemes, the use of insulation standoffs, and sealing and finishing systems have all been improved.

The benefits of these improvements should be evident during in-service performance of the Boeing and future aircraft. Liberal use of corrosion-preventive compounds applied in the aircraft assembly process and periodically in service, using a good corrosion control maintenance program, should minimize future corrosion concerns. As discussed in chapter 4 , prior to the latest generation of aircraft, which includes the Airbus A and the Boeing , structural composites have been used on aircraft flight control surfaces such as elevators, spoilers, ailerons, and rudders, as.

For these applications, honeycomb sandwich designs with thin 0. It follows that most of the experience with advanced composites has been obtained with this kind of construction. Previously, similar constructions with fiberglass skins and nonmetallic honeycomb core have been used.

There is much less service experience with thicker-skin laminate designs that have been used in composite primary structure. In general, the service experience with composites indicates that damage occurs because of discrete sources such as impacts, lightning strikes, and handling rather than progressive growth caused by a fatigue condition Blohm, In addition to groundhandling damage, a recent survey by the International Air Transport Association, summarized in table , lists the particular causes of damage that occur in the current generations of composite structure IATA, The types of damage to composite components include disbonds or delaminations 45 percent , holes or punctures 35 percent , cracks 10 percent , and other damage 10 percent.

An especially difficult maintenance issue resulting from these types of damage is when perforation allows the incursion of hydraulic fluids, water, and other liquids into the honeycomb core.

Composites may also suffer loss of load-bearing capability due to resin charring and the potential for corrosion of adjacent metallic surfaces. Typical causes of composite service damage mechanisms are shown in table Service experience with thicker composite laminate constructions, such as that used on primary structures on the Airbus A and Boeing , is not adequate enough to establish damage trends.

The current methods used by the airlines to repair damage to aircraft composite structure secondary structure and primary flight controls depend on the extent of damage, the time available to perform the repair, and the time until the next scheduled maintenance visit.

What effect does all this offshoring have on the airworthiness of the fleet? In , an Air France Airbus A that had undergone a major overhaul at a maintenance facility used by U. The plane traveled first to Paris and then to Boston, where mechanics discovered the problem. The company that performed the work also does maintenance for American.

Air France has denied that the problems were associated with maintenance done in China. In , a US Airways Boeing jet carrying passengers from Omaha to Phoenix had to make an emergency landing in Denver when a high-pitched whistling sound in the cabin signaled that the seal around the main cabin door had begun to fail.

In , a China Airlines Boeing took off from Taiwan and landed in Okinawa only to catch fire and explode shortly after taxiing to a gate.

Miraculously, all people on board escaped without serious injury. Investigators later concluded that during maintenance work in Taiwan mechanics had failed to attach a washer to part of the right wing assembly, allowing a bolt to come loose and puncture a fuel tank. China Airlines does maintenance work for about 20 other carriers. Airline mechanics at U. American Airlines mechanics contended in a lawsuit last January that they had been disciplined by management for reporting numerous safety violations they uncovered on airplanes that had recently been serviced in China.

Mechanics in Dallas said they had discovered cracked engine pylons, defective doors, and expired oxygen canisters, damage that had simply been painted over, and missing equipment, among other violations. The F. Even engine repairs and overhaul—the highly skilled aircraft-maintenance work that has remained largely in the U. Not everyone in official Washington is oblivious to what has been happening. It needs to know where maintenance work is being done, and by whom. In , the inspector general called on the F.

Twelve years later, the agency still has no such requirement. As a result, aircraft are being parked in a variety of places. Delta also has over 80 aircraft stored in each of Marana, Arizona, another boneyard, and Birmingham, Alabama, both in the US, Petchenik says.

American, in addition to its hub storage, has aircraft parked in Tulsa and Pittsburgh [in the US states of Oklahoma and Pennsylvania, respectively]. Larger airlines are clustering similar aircraft together; some need certain maintenance, and having engineers who specialise in those types of planes in the same place makes sense. American Airlines, for example, is using four airports: its Airbus A, A and A aircraft, as well as Embraer E regional jets, are parked in Pittsburgh, the airport that used to be a hub for US Airways which merged with American in but which has had extra space to offer since.

Roswell, in the US state of New Mexico best known for a more interplanetary kind of visitor , is now temporary home to Boeing , , and aircraft. Like any airport parking lot, the rates an airline pays to park its planes depend on how convenient the location is. Space at larger and more important airports tends to be more expensive, and is also limited, which is why airlines are flying their planes to out-of-the-way places.

In Europe, some airlines have grounded their entire fleets, while others are keeping a few key aircraft ready to perform repatriation flights, fly critical medical and other cargo around the world, or as otherwise agreed with their national governments. When it comes to storage, a similar patchwork of solutions is in place. It is pressure-sensitive, approved for use by the Federal Aviation Administration FAA , and engineered to adhere to the airplane fuselage, even when traveling at mph, the typical cruise speed of a Boeing Should your aircraft need more serious fixes, rest assured that the flight will be delayed or the plane taken out of service until maintenance has completed and signed off on the work.

Speed tape is one of those.