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During the past few years, regional jets have received increasing attention in the press. While RJs, as they are popularly called, have been welcomed by some observers as saviors of high-quality jet aircraft service to small communities, they have also been vilified by others as being largely responsible for the delays experienced by airline passengers throughout the past two summers.

In 1997, in an effort to provide a preview of the potential impacts of RJs on the air traffic control (ATC) system, CAASD investigated the underlying operational and economic environments of RJs. This work has elicited extensive attention in both the media and the aviation community.

CAASD¿s analysis demonstrated two distinct trends: 1) that growing airspace and airport congestion was exacerbated by the rapid growth of RJ traffic; and 2), that potential airport infrastructure limitations may constrain airline business. Of particular concern was the high-altitude en route airspace between Chicago, New York, and Washington, DC. Until recently, airspace congestion had received limited attention in comparison to airport congestion. But with delays and congestion at all-time highs, that has changed.

Because they are jets, RJs operate most efficiently when flying at higher altitudes. Unfortunately, that airspace is already congested during peak travel hours in parts of the country. And since some RJ models fly slower than larger narrowbody jet aircraft, some traffic flows are disturbed.

Furthermore, there are many en route and airport routes specifically designed for the turboprop aircraft that RJs are replacing¿yet those routes are receiving less traffic as jet routes become increasingly crowded. In addition, some turboprop runways are too short for RJs to use.

A Snapshot of Regional Jets in the Fleet

As this chart suggests, while there are only about 500 RJs in the combined U.S. commercial airline fleet today, the major airlines have some 750 RJs on order, with options for another 1,250. As CAASD¿s RJ studies demonstrate, this dramatic change from the handful of RJs that were in operation only 5 years ago has major implications for the NAS today and in the immediate future

CAASD¿s early warning of impending problems associated with the spectacular growth of RJs provided some with a "wake-up call." RJs are likely to be a regular feature of the airline industry for a long time: Passengers overwhelmingly prefer RJ service to turboprop service, as do the airlines that operate them. From the passengers¿ perspective, they are far more comfortable; and from the airlines¿ point of view, they are more profitable. Thus, within a few years, most regional air traffic in the continental United States will be by jet, with turboprops filling a minor niche role.

During the spring and summer of 2000, the FAA, CAASD, major airlines, and others focused on finding mitigating strategies to address airline congestion. With more than 500 RJs in current use¿and doubling expected over the next few years¿the success of efforts such as these is critical if growth in the regional airline industry is to be sustained.

RJs still represent a small fraction of the total U.S. airline fleet, and are no more responsible for congestion and delays than the thousands of other aircraft in operation. Their use as turboprop replacements may have hastened the onset of congestion at a few locations, but it was only a matter of time before we would have faced those challenges.

What needs to be kept in mind is that small cities throughout the nation now enjoy better airline service because RJs can provide long-distance capabilities that enable access to many more airline hubs than turboprops.

Helping FAA officials, airline executives, policy makers, and the general public understand the implications of this technological shift is one of the ways CAASD fulfills its charter of working in the public interest.

Regional Jets

Regional jets, RJs in common parlance, are enabling the continued rapid growth in passenger traffic carried by the regional airline industry. Regional airlines will, according to the Regional Airline Association, carry more than 84 million passengers by the end of 2000. This is a staggering 1000 percent increase from the 7.2 million passengers they transported only a quarter of a century ago in 1975. The downside of this remarkable growth is that, in combination with the growth in major airline traffic, many of the most active U.S. airports have been pushed to capacity, resulting in increased air traffic control congestion and unprecedented delays in scheduled flights.

One of the conundrums associated with RJs is that while they are generally smaller than the jets in the major commercial airline fleets¿current models range from 32 to 85 seats--they are designed to fly at the same higher altitudes as the larger jets. (Note that there is no unique definition of RJs, but most current models range from 32 to 50 seats. However, some people consider jets that carry as many as 10 passengers RJs. However, most people do not consider aircraft built by Boeing or Airbus to be RJs, so the most common definition is that RJs are commercial jet aircraft that carry fewer than 100 passengers.) In replacing the turboprop-driven aircraft that constituted the current generation of aircraft flown by the regional airlines, RJs have moved regional airline traffic from the lower altitude domain of the turboprops into the increasingly crowded airspace where the larger jets fly. At least two factors are at work here. Passengers prefer the comfort that jet travel offers in being able to get "above the weather." And then there are economic considerations: It is often more efficient on shorter routes for the slower prop-driven aircraft to operate at lower altitudes than to waste time and fuel getting above, say, 20,000 feet. But because they are jets, RJs are more efficient at much higher altitudes.

To give some indication of the size of an RJ, Figure 1 shows the seating layouts for three aircraft: a Boeing 737-700 (seating 112 in this two-class configuration), a 50-seat Canadair CRJ, and a 19-seat J31 turboprop. It should be noted that the Boeing 737, probably the most popular commercial jet in service today, is not an RJ, even though it is considerably smaller than the larger commercial jets.

Canadair CRJ

J31 Turboprop

Pioneering Regional Jet Research at CAASD

In 1997, in an effort to provide an early, analytically based preview of the potential impacts of RJs on the air traffic control (ATC) system, the Center for Advanced Aviation System Development (CAASD) investigated the underlying operational and economic environment of the regional airline industry¿s use of RJs. Since then, the results of this work have elicited extensive attention. The analysis began as part of an FY98 FAA-sponsored research project entitled NAS User Operations and Economics.

CAASD found potential future changes in the volume and pattern of air traffic due to the increasing use of RJs in air carrier operations. Specifically, we highlighted concerns about growing high-altitude airspace and airport congestion contributed to by the rapid growth of RJ traffic and concerns about potential airport infrastructure limitations that may constrain regional airline business plans. This early warning was first made in 1998.

One chart in particular drew special attention. It illustrated the geographical distribution of future congestion in en route airspace, with particular concerns discussed about the airspace in the Cleveland and Indianapolis centers. Until recently, airspace congestion received limited attention in comparison to congestion at airports. However, as a result of increasing demand, thunderstorms, and other factors, concerns about airspace congestion are now a part of the public attention.

Figure 2. En Route Congestion Across Centers

The rate of growth of RJ traffic is aggravating an already difficult situation. Many large airports are near or at full capacity. Even those with expansion plans will have difficulty keeping up with the growth in air traffic that is anticipated over the next ten years. At other airports, where there are no plans for new runways in the foreseeable future, airline plans may be stymied by an inability to increase traffic without bringing on gridlock. In the air the situation is no better. Already, the high altitudes flown by jets are much more crowded than the lower altitude airspace where turboprops fly. As turboprops are retired and more long-distance RJ flights are added, this situation will get worse. The FAA is in the midst of a major, system-wide modernization effort, but the airline industry is pre-senting a moving target of ever higher traffic levels to be handled. The additional congestion from RJs will affect not only RJ traffic but all other jet traffic in the US as well.

Background on Regional Jets

Regional jet traffic in the continental US is expected to continue its rapid growth for the next several years as the regional airline industry continues to procure and deploy RJs at a very fast pace. Comair, a regional airline that feeds Delta in Cincinnati, was the first to introduce new-generation RJs in 1993. Today, there are about 500 of these 32¿50-seat jets in operation in the continental US. The number on hand and on order, including options, is nearly 2,500 aircraft. The 1,300 aircraft on-hand plus firm orders is nearly the same as the number of turboprop aircraft based in the continental US. Most of the firm orders are scheduled for delivery by 2005. It is important to note that these figures are current as of August 2000, and, given the frequency of new RJ orders this year, could quickly become obsolete.

As a result of this rapid growth, the regional airline fleet is evolving from almost exclusively turboprops to a mix in which small jets will soon equal or possibly even outnumber turboprops. In combination with the growth in other jet traffic, this evolution has potentially significant ramifications for the air traffic management (ATM) system¿s ability to accommodate the airlines¿ plans for traffic growth. Some of these effects are already present¿recently, RJs have been blamed by some people in the aviation industry as major contributors to this summer¿s record-setting delays.

Passenger Demand

As noted above, passengers have clearly demonstrated their preference for RJs to propeller-powered aircraft almost everywhere they¿ve been introduced in the U.S. In general, service by RJs has been accepted as at least equal to service by larger jets. Smaller cities see these small jets as saviors for airline competition and as providers of critical access to air travel. Airlines embrace RJs because 50-seat jets let them offer high-revenue business travelers the high frequency service and more convenient same-day round trip schedules they prefer at lower per-hour operating costs than the much larger jets.

Because of their size, speed, and range, RJs have made many more city-pair combinations operationally and economically feasible today than was possible just a few years ago. While RJs are mostly used in today¿s markets to expand hub support, someday they may also be used in large numbers in a hub-bypass role. While it is not yet clear what traffic flow patterns will look like in ten years, it is clear that they will be different than they are today.

The Effects on Air Traffic Management

The net effect of the growth in RJs is a change in both the volume and pattern of air traffic. This growth has potentially significant ramifications for both airport and airspace requirements in the very near future. From an ATM perspective, RJs operate at airports like larger narrowbody jets. Their climb and descent performance more closely resembles mainline jets than the turboprops they are displacing. As a result, the prop-jet fleet mix in terminal area airspace and the demands on runways are changing significantly. Yet in terminal airspace, some models of RJs tend to climb and cruise more slowly than most other jets in the US fleet. In the air, the route structures in place for merging and sequencing traffic are generally designed to accommodate separate turboprop and jet flows. Therefore, the changes in fleet mixes cause a redistribution of traffic among these routes. In addition, some runways at several important airports that are currently used by turboprops may be inaccessible to RJs, either because they are not long enough or because of limits due to noise abatement rules.

High altitude en route airspace in the US typically starts at 24,000 feet. RJs prefer to cruise at altitudes above that level, and preferably in the 30,000¿35,000 foot range, for flights with stage lengths of 300 miles or greater. Since most RJ flights exceed that distance, RJ flights are likely to request access to high altitude airspace.

By contrast, turboprops rarely operate at such high altitudes. This is occuring while business jet and large commercial jet traffic also has continued to grow. The predicted result has been additional congestion in high altitude airspace and, as turboprops are removed from service, decreasing traffic in low-altitude airspace. As airlines add more RJs to their fleets, it appears likely that high-altitude airspace may become significantly more congested, particularly in the Indianapolis and Cleveland centers. We have already begun to see that problem over the past year. In addition, airlines will be creating additional high traffic demands at their busiest hub airports, especially in the already strapped eastern U.S. region, from Chicago¿s O¿Hare airport at the western perimeter, to Newark, New York LaGuardia, and Boston Logan airports to the east.

In short, RJs operate much like other jets, with some of the significant differences noted above. As a result, we are experiencing a natural evolution toward more jet travel, just as jets replaced large commercial turboprops several decades ago. What we are also seeing are the side-effects of the evolution of the airlines¿ fleets toward more jet flying¿what might be called "growing pains." The primary result, from an air traffic management perspective, is that there are simply are more jets flying. At a secondary level, some of these new jets, the RJs, operate slightly differently than other, larger jets. But we have had a heterogeneous fleet for years¿now is no different.

Status Update

Figure 3. Regional Jet Inventory and Orders

In November 1999, CAASD updated some of its assumptions underlying the RJ study. In

June 1998, when the original demand scenario was constructed, only 200 RJs were in operation, versus 500 now. The following chart shows the current orders on the books for the purchase of new aircraft (based in part on educated guesses as to which major airline¿s code some aircraft will fly). In order to reach the estimate of 800 RJs in operation by December 2003, the June 1998 estimate of 800 RJs required the assumption that a sizeable number of options would be exercised. By November 1999, firm orders had grown to nearly 900 RJs with options for 800 more. Since then, there have been many more orders still, bringing the totals to about 1300 firm orders plus over 1100 options. As such, an estimate of over 1000 RJs in operation by the end of 2003 can be readily made without resorting to assumptions about options. Now, it¿s only a matter of examining the delivery schedules of orders placed under firm contract with the manufacturers.

Figure 4. Forecasts of Regional Jet Fleet

As evidence of the continued rapid growth in RJ purchase plans, the study was based on a demand scenario in which 800 RJs would be operating by the end of 2003, with fewer than 500 by the end of 2000. After only two years we are already one-half year ahead of schedule with more than 500 in service. Based on this pace of deployment, we now anticipate that there will likely be nearly 1100 RJs operating by the end of 2003, with potentially no reduction in their deployment rate for several years after that.

Figure 5. Mix of Airport Traffic by Aircraft Type

Although some observers have blamed RJs as contributing to recent airspace and airport congestion, they certainly are not alone in contributing to it. RJs still represent a small fraction of the total U.S. airline fleet, and are no more responsible for congestion and delays than many of the other thousands of aircraft currently in operation. Their use in adding new capacity and as turboprop replacements may have hastened the onset of congestion at a few locations, but it was only a matter of time before we would have faced those challenges anyway.

The challenge now for the aviation industry is now to find ways to leverage the improved service quality provided by RJs while mitigating the congestion and delays that have become all too common.

On the Horizon

There are several issues that are likely to remain hot topics with respect to RJs: scope clauses, operating performance and the impact on en route air traffic flows, and operational performance at airports. Each of these subjects is briefly touched on below, and may warrant further research to clarify the issues.

Scope clause. The scope clause is part of the collective bargaining agreement between an airline and its pilots¿ union, defining who shall perform flying on behalf of the company and under what circumstances. Basically, this is the language that provides job protection for pilots by placing limits on the use of code sharing, which is viewed as outsourcing by the pilots. It affects all code-share flights, including international partnerships and what traditionally been referred to as commuter traffic. In some cases the language is very specific in terms of identifying particular aircraft types and what types of routes may be flown. This is a critical issue for major airline pilots because prior to the arrival of regional jets, it was the engine type that distinguished between their flying and that of their regional partners. Even then, there was controversy in cases where routes were handed down from a major carrier to its regional carrier, particularly when this occurred in concert with layoffs at the major. Because RJs are jet aircraft and the size of some planned models overlaps that of mainline aircraft, there are some strongly held and conflicting opinions.

In the meantime, several airlines are tightly constrained as to the maximum number of RJs that can be flown under their carrier code, while other airlines have considerable freedom to operate large numbers of RJs. For example, Delta currently has a relatively nonbinding scope limitation with respect to RJ flying; as a result, there are already more than 150 RJs flying as Delta Connection. Including the aircraft under firm contract will bring them up to nearly 400 in the next few years. In addition, there are more than 450 options held by Delta regional carriers. In contrast, USAirways and TWA are very tightly restricted to a few dozen RJs that can fly for them. Given the importance of feeder traffic to the success of hub-and-spoke systems, this is a critical issue for the major airlines that has yet to be resolved. Part of the uncertainty also relates to who will fly the new 70¿110 seat aircraft that are being planned for production within a few years.

Cruise performance. Some air traffic controllers have allegedly complained about the slow speeds and climb rates of RJs in the en route airspace environment. To the extent that this is true, this becomes a potentially serious issue when a RJ is in front of a faster jet that wishes to pass. In uncongested airspace this is not a concern, but in the Cleveland and Indianapolis Air Route Traffic Control Centers, this has recently been the subject of some controversy due to the increasing high-altitude congestion those centers have experienced. In practice, however, there is considerable misinformation about the operating performance of RJs. Most aircraft currently in service and the vast majority of newly purchased aircraft operate at speeds nearly identical to the lower end of the range of the narrowbody fleet used by the major airlines.

Airport performance. There are at least three issues here. First, RJs are jet aircraft, not turboprops, and some runways at a few important airports are restricted to use by only turboprops as part of prior agreements made with local communities during the approval stage. At the time, this streamlined the negotiations over noise levels because jets of the day were much larger than turboprops and were considered to be much noisier. Unfortunately, modern RJs that are nearly as quiet as turboprops are not allowed to use such runways.

Second, some air traffic controllers claim that RJs cannot turn in the air as quickly on departure compared to turboprops. In a few cases, this prevents them from flying the same departure routes that turboprops fly at a few airports where airspace is very restricted. As a result, even in some cases where there is no explicit rule preventing jet use, the tightly constrained airspace does not allow RJs to use traditionally "commuter" runways (that have frequently been utilized by regional aircraft in the past) when departing the airport. Although it may be possible to redesign some departure routes, the required environmental impact studies will take time to conduct and may be difficult to get approved.

Third, because most RJs require a greater runway landing distance than turboprops, some short runways cannot be used by RJs. In a few cases, where turboprop service was replaced by RJ service, this has had the effect of adding traffic to the jet runways that may already be overcrowded during peak arrival and departure times.

Date Posted: September 28, 2000