Political and media pressure have encouraged the FAA to expand its pursuit of real and perceived problems of older aircraft and their systems. Operators will pay.

Dassault Falcon 50 vintage 1977

For most operators, the answer to the question of when is an airplane or helicopter too old is straightforward: when its economically useful life ends. In the real world, that answer is not so simple. Given the wide variety of applications, geographic areas, regulatory oversight and economic drivers, aircraft once thought to be candidates for the wrecker's yard by one group are considered very useful by another.

The Douglas DC-3/C-47 is the hands-down winner in terms of useful life, but there are many other examples, from old (and not so old) passenger transports that find new life converted to freighters to corporate expresses that become small package carriers.

The FAA has been taking a different approach to determining useful life. Its interest was given impetus by the 1988 Aloha Airlines 737-200 accident, in which the airplane had a structural failure and attendant explosive decompression. The proximate cause was traced to corrosion and debonding of skin lap joints in the upper forward fuselage. It is worth noting that operators and manufacturers already had become concerned with airplanes that were reaching or had passed their design life (variously measured in terms of years in service, hours flown or cycles accumulated). The accident accelerated attention to the characteristics and causes of structural aging.

Cessna Citation, 1975

A Tangled Web

Most of the attention has been focused on airplanes used in scheduled passenger operations. However, changing regulatory notions in part spurred by the "single safety standard" embraced by former Secretary of Transportation Federico Peña have increased the impetus towards a one-size-fits-all approach to rule writing. It already is clear that regulatory initiatives are trickling down through operating categories. If the past is any guide, the FAA is likely to broaden its efforts to encompass more types of aircraft and operators. As the community has already experienced with such efforts as reduced vertical separation minimums (RVSM), flight recorders and ground proximity warning systems, the cost to retrofit certain older designs hastens the end of their useful economic life.

Regulation writers also are broadly interpreting congressional and international treaty mandates as applying to more operating categories than were originally intended.

Changing Certification Philosophies, Changing Competence The burdens are being compounded by the current regulatory notion that the current state of the art must be applied to all aircraft, regardless of the original certification basis.

Broadly stated, the U.S. government aircraft certification philosophy has progressed through four main phases:

• Structural strength. Does the design have sufficient structural strength to tolerate known, anticipated flight loads? There was no fatigue criteria applied.
• Safe-life. In the early 1950s, knowledge about fatigue was accumulating. Certification was based on the assumed safe life of the principal structure and components before structural flaws developed that could result in catastrophic failure. Design lives were established that were expressed in years, hours or cycles.
• Fail-safe. By the late 1950s, led in part by the increasing development of pressurized fuselages, the regulators embraced the requirement to design multiple load paths so that the failure of one principal structural element (PSE) would transfer aerodynamic loads rather than lead to catastrophic failure. (The FAA defines a PSE as "those which contribute significantly to carrying flight, ground and pressurization loads, and whose failure if it remained undetected could result in catastrophic failure of the airplane.")

  The requirement to inspect for structural integrity also became more fully developed and replaced the earlier, fix it when it breaks, approach.

• Damage tolerance. The concept assumes that structures will fail and requires the development of structural inspection procedures (SIP) to monitor continuing airworthiness and detailed structural repair procedures and documents. Manufacturers must limit safe life design methods to ground loaded, single load path, structures such as landing gear.

The FAA now is moving beyond damage tolerant design to a higher level that assumes the existence of what it calls an "initial flaw" -- a structural flaw introduced in the manufacturing process -- which the structure must accommodate until it can be detected in later inspection.

IAI Westwind 1123, 1974

Changing the Rules

So, even when an FAA official predicts the time a new rule will be released, don't bet on it. For example, FAA rule writers involved were certain that a significant new regulation affecting aircraft modification would be released in December 1999. It still is on hold.

However, when it is released it is bound to have widespread effect, as even the FAA admits. The summary of the original notice of proposed rulemaking (NPRM), issued in mid-1997, is quite descriptive:

"This document proposes to amend the procedural regulations for the certification of changes to type certificated products. The amendments are needed to address the trends toward fewer products that are of completely new design and more products with repeated changes of previously approved designs. Safety would be enhanced by applying the latest airworthiness standards, to the greatest extent practicable, for the certification of design changes of aircraft, aircraft engines and propellers."

The proposed rule would greatly affect the way in which STCs are obtained. Cost would rise. An FAA official agreed that it would have a "large impact upon virtually everyone." It most certainly would affect modifiers that seek to extend the useful economic life of older designs.

Learjet 24D, 1972

The FAA Approach to Useful Life Extension Another NPRM in limbo -- which is holding up the issuance of two related advisory circulars -- more clearly shows the direction of FAA thinking about older airplanes.

In brief, the NPRM -- which is a redraft of the original, 1993, proposal -- would require the development of structural inspection programs (SIP) in accordance with damage tolerance concepts. Airplanes in service for 25 years or more would have to be inspected within three years; those 14 and over would have to be inspected within five years. Operators would have to comply or ground affected airplanes. In the draft NPRM, the FAA estimates that there were 1,550 airplanes 24 years or older in 1998 that would be affected and 2,850 15 years and older.

The agency notes in the NPRM that supplemental inspection procedures already exist for many aircraft (Advisory Circular 91-60 outlines procedures for these inspections). However, it now considers these inadequate because they are "derived from service history and the analysis of fleet leader experience rather than damage-tolerance based engineering analysis." So the new thinking bypasses the traditional experience/service bulletin/airworthiness directive process.

In announcing the draft, B/CA (May 1999, page 32) said "New rules requiring fatigue crack inspections of aging regional aircraft could signal the `death knell' for many piston and turboprop twins in commuter service."

While many manufacturers have established design life goals for aircraft and for principal components (Boeing, for example, used a theoretical 20,000-hour economic life when designing many of its airplanes), the FAA has decided airplanes are old at 14 years if they are used to carry passengers for hire. The proposal would apply to all airplanes operated under FAR Part 121, all U.S.-registered multiengine airplanes operated under Part 129 and all multiengine airplanes used for scheduled operations under Part 135. Ominously, the proposal further notes that rotary-wing and single-engine aircraft would be excluded "for now."

The FAA, which frequently is criticized for the poor quality of its cost analysis, calculates the cost of the NPRM at nearly $200 million, including more than $95 million to develop and implement the SIPs. Operators would be required to notify the FAA before undertaking the required inspection, which would be closely monitored by the FAA or inspectors with delegated authority. Record-keeping and reporting requirements also would become more specific and extensive.

Demonstrating a high level of understatement, the FAA noted that the program will be "difficult to administer." The rule writers acknowledge that, "For some airplane models, the potential unit costs of the proposal could constitute significant proportions of, or actually exceed, the economic values of the airplanes involved." Nevertheless, Congress required such action when it enacted the Aging Aircraft Safety Act of 1991, according to the FAA.

In explaining the rationale, the NPRM states that "The FAA believes that the damage-tolerance based inspections and procedures . . . are the best approach to assure the continued safety of the subject fleet while striking the most cost-effective balance of fully responding to the law, minimizing overall costs and minimizing the impact on small entities."

A number of operators and organizations do not consider the impact of the proposed rule quite as benign as the FAA had intended. Several wonder how the proposed monitored inspections can be imposed -- and, more important to affected operators, how SIPs can get approved in a timely manner -- with the shortage of qualified FAA people and the continuing budget problems that curtail travel and other activities.

The decline in practical knowledge and experience displayed by a wide variety of FAA employees has been observed and reported widely and frequently. One negative aspect is that it places additional burdens on the regulated. More time and resources must be placed on participating in rule formation where possible and in reviewing proposals before they become law. After the fact, much time and energy is spent seeking redress from poorly conceived and drafted regulations. The FAA also has been consistently transferring the regulatory burden from government to the user.

The FAA recognizes that developing SIPs may be impossible for some designs. The NPRM notes that "the manufacturer may have gone out of business; technical data may not be adequate; the technical knowledge base may no longer be readily available" and developing the required inspections and procedures might not make economic sense.

Given the number of affected airplanes that are no longer in production and the lack of interest by their former manufacturers in undertaking the substantial engineering effort to develop SIPs, the effect on smaller operators could be catastrophic (the initially targeted airplanes are listed in the accompanying table). As Richard Peri, National Air Transportation Association manager of technical services, observed shortly after the current NPRM was released, "Asking a small air carrier to replicate the engineering expertise and experience base of large aircraft manufacturing firms is unrealistic." He went on to say that the "agency has, with the stroke of a pen, devalued the assets of small businesses worldwide."

Operators of airplanes that have had after-market modifications might find the challenge even more daunting. The NPRM notes that for airplanes modified under an STC, the original equipment manufacturer "may not have sufficient technical data" about the STC. Also, "the operator may not be able to work with the STC holder or manufacturer." In that case, the operator can either develop an SIP independently or take the airplane out of service.

In its formal response to the NPRM, the Regional Airline Association (RAA) said the "high costs associated with complying with the proposed rule will be disproportionately borne by operators of fleets with non-damage-tolerant airplanes; yet the service experience for such fleet types . . . does not justify the high cost of converting to a damage-tolerant inspection program."

The RAA objected that the final proposed rule neglected the work of the association, members and manufacturers that served on the Small Transport/Commuter Airplane Airworthiness Assurance Working Group (SAAWG) for two years to develop an alternative inspection program that would "more effectively address the safety concerns" of older airplanes than the NPRM.

The organization further challenged the FAA claim that the NPRM was driven by the Aging Aircraft Safety Act of 1991.

The RAA has asked that the entire NPRM be withdrawn. The group's formal response, signed by David Lotterer, vice president of technical services, lists many technical objections as well as pointing out that some requirements, including the record reviews, duplicate current rules.

Gulfstream II, 1972

But Wait, There's More

The NPRM and ACs can be obtained on the Web at www.faa.gov/avr/ arm/nprm.htm. It is worth noting that the NPRM in draft form is 105 pages long.

The RAA objected to the final form of AC 91-MA, claiming that the FAA made a last-minute switch "to specify a damage-tolerance based program as the only method of compliance." It points out that the draft AC 91-72 developed by the SAAWG provided for other supplemental inspections. AC 91-MA is a substantially revised version "accomplished by the FAA without industry coordination."

The FAA is pursuing other avenues related to real and presumed issues of aging aircraft. The TWA 800 and Swissair 111 accidents increased agency focus on non-structural systems, particularly electrical systems. The agency formed a task force of certification and flight standards people to investigate potential issues. Among other activities, the group, assisted by Boeing engineers, inspected several airplanes during heavy maintenance activities. The group focused on wiring, lightning protection, and flight control and hydraulic systems. It also evaluated incident, accident and service difficulty reports.

The study group found deterioration in and contamination of electrical systems and determined that "Current maintenance practices do not adequately address wiring components" and that inspection and reporting guidelines were too general. It also called for more testing and "better inspection criteria" for flight control and hydraulic systems.

In 1998, the "FAA Aging Transport Non-Structural Systems Plan was issued and the Aging Transport Systems Rulemaking Advisory Committee was formed. Among the mix of government certification authorities (FAA, JAA, Transport Canada), manufacturers and organizations, the sole general aviation representative is GAMA.

One of the tasks established was to study the impact of aging on "flight-critical electronic control systems, their wiring, and their lightning and HIRF protection." The plan specifically recommended the Boeing 757 and Airbus Industrie A320 be evaluated since they are the earliest designs with such electronic controls.

Another issue raised in the plan is whether a service life limit should be developed for electrical wire and "if appropriate, establish the service life of all types of airplane wire used in transport airplanes" and develop non-destructive testing (NDT) methods and tools for wire. The FAA also wants to evaluate whether "aging airplane components like wiring, circuit breakers, connectors, pumps, motors, harnesses removed from airplane during maintenance, be examined . . . for safety implication of failure."

Not all the rules we must operate by are contained in the FARs -- not to mention the variations in interpretation among the many FAA offices or even between individuals within an office that can change the rules. While advisory circulars are supposed to be just that, many FAA officials interpret them as the law. Internal guides, such as inspectors handbooks and changed orders to them, can be useful to operators. There are separate handbooks for air transport and general aviation inspectors. These can be accessed on the Web at www.faa.gov/avr/afs/hbat/hbatl.htm  and www.faa.gov/avr/afs/fsga/fsgal.htm , respectively.

The rules are changing. Following the developments in air transport can provide an early indication of potential changes of requirements for business aviation. The significant degrees of change imposed by such regulations will have great effects on corporate travel management in such areas as fleet decisions and budgets. B/CA

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From the March 2001 issue of Business & Commercial Aviation magazine. Copyright 2001, The McGraw-Hill Companies, Inc.