Is it time to rethink the regional jet strategy?

In a working paper published late last year, I established that the amount of CO2 produced each kilometer when transporting a passenger on a flight less than 500 km was nearly double that of flights over 1000 km in distance. This is because the extra fuel used for takeoff is relatively large compared to what is used during the cruise segment of the flight, and due to the use of less fuel-efficient regional jets with 76 or fewer seats on the shortest flights.

So, why are airlines still using these smaller planes? Not only does the use of regional jets work against the aviation industry’s goals to improve fuel efficiency and reduce CO2 emissions, passengers typically hate flying on turboprops and regional jets. The airlines will tell you they use smaller aircraft to serve small- and medium-sized cities where it is not economical to use narrowbody aircraft and feed them through their hubs. In existing markets, the use of regional carriers allows for an increase in flight frequency and, therefore, more flights per day at smaller airports.

Let’s take a look at the use of regional aircraft by the three largest U.S. air carriers – American, Delta, and United – and their regional affiliates since 2009. For this analysis, data was obtained from the airlines’ annual financial or quarterly operations filings. Operations and fuel data for US Airways, Northwest, and Continental have been combined with the data for American, Delta, and United, respectively, for years prior to each airline merger.

In 2018, nearly half of flights for the three airlines were operated by a regional carrier. As shown in Figure 1 below, more than 60% of flights of 1000 miles or less were flown with smaller aircraft, with nearly three quarters of the shortest flights flown with regional jets. According to 2018 annual reports, none of the regional aircraft operating for American, Delta, or United were turboprops.

Graph: % of departures in the distance band
Figure 1. Flights by aircraft class and distance, 2018.

Since 2009, total capacity of the three airlines increased by 14%, to a total of 820 million available seat miles (ASMs) in 2018. The capacity offered by regional aircraft increased at a slower 3% over the 9 years to 90 million ASMs in 2018. The slow growth in regional aircraft capacity is partially due to some on airlines adding more premium seating on their aircraft in an effort to differentiate their services from the competition. Delta decreased ASMs on smaller planes by 20%, while American increased theirs by 34%. Seats available on United Express flights have fluctuated over the years, but the airline flew 1% more ASMs in 2018 than in 2009.

Over the 9-year period, the passenger load factor of the regional aircraft for these three airlines increased 5 percentage points, from 75% of seats filled to 80%. The passenger load factor for the aircraft used in mainline flights increased from 82% to 84%. The increase in capacity and the increase in the number of passengers per flight equates to an increase in revenue passenger miles (RPMs) over the period—18% for mainline operations and 8% for regional operations.

Total fuel consumption for the combined American, Delta, and United fleets increased 5% since 2009, to 12.7 billion gallons in 2018. Fuel consumption for regional aircraft increased 5% over the 9 years and accounted for 16% of total fuel burned by the three carriers in 2018.

Across the three airlines, fuel efficiency has increased between 7% and 10% since 2009, depending on whether it is calculated based on ASMs or RPMs flown. Figure 2 below shows the trend in fuel intensity, or fuel consumed per 1000 RPM, for mainline and regional aircraft. A 1% decrease in fuel intensity represents a 1% increase in fuel efficiency. Between 2009 and 2018, the fuel intensity for narrowbody and widebody mainline aircraft decreased by between 9% and 13% depending on the airline, while the fuel intensity for regional aircraft improved less, with each carrier showing between a 1% increase to a 7% decrease in fuel intensity.

Figure 2. Fuel intensity for the three largest U.S. air carriers (mainline and regional operations), 2009-2018.
Figure 2. Fuel intensity for the three largest U.S. air carriers (mainline and regional operations), 2009-2018.

The main takeaways from Figure 2 are that fuel efficiency for larger aircraft is increasing at a faster rate than for regional aircraft, and that the smaller jets burn 60% more fuel per passenger mile than larger jets. One reason for the increased fuel efficiency gains of the mainline fleet compared to the regional fleet may be the replacement of older narrow- and wide-body aircraft with newer, fuel-efficient models, while the regional aircraft are all relatively new. According to, the average age of the mainline fleet for the three air carriers is between 11 and 16 years, while the average age of the regional fleet is 7-10 years.

While the aircraft in the regional market tend to be newer than the mainline fleet, there have not been significant technological advancements to improve environmental performance like we have seen with the Boeing Dreamliner and Airbus A350. New generation, more fuel-efficient regional jets are being developed, such as the Embraer E175-E2 and Mitsubishi SpaceJet, but there are currently no orders of either aircraft by a U.S. airline. When it comes to turboprop aircraft, there hasn’t been a new turboprop engine in decades even though they’ve been shown to be the most fuel-efficient of regional aircraft.

Despite evidence that regional carriers tend to have higher rates of fuel consumption, it is highly unlikely that three carriers will sell or end their relationships with regional airlines in order to reduce CO2 emissions. However, there are some developments on the horizon that would improve the environmental performance of these shorter flights.

While aviation faces unique challenges concerning electrification because the performance of airplanes is extremely sensitive to their mass, zero-emission technologies are ideal for use in smaller aircraft. Indeed, aircraft manufacturers around the world are working on smaller electric aircraft that could cover the flight distances that most regional jets are currently serving. 

The use of sustainable biofuel in smaller aircraft could have also have a positive impact, particularly if it’s produced locally. Although alternative jet fuel production is currently quite low—the amount of biofuels produced in 2018 would fuel the global commercial aircraft fleet for 10 minutes—air carriers are starting to make commitments and investments. Delta Air Lines recently announced their intention to purchase 10 million gallons of biofuel a year. This is a positive step, even if it can only replace 10% of the fuel it uses for West Coast operations.

In the future, regional carriers could also consider purchasing different aircraft and refraining from offering more premium seating. It’s also possible that applying different utilization strategies could make a difference in ensuring the convenience of short flights from smaller airports does not result in double the CO2 emissions.

Tracking progress