Trunk carriers or trunk airlines or trunklines or trunks, were the US scheduled airlines certificated in the period 1939–1941 by the Civil Aeronautics Authority (CAA) or its immediate successor, the Civil Aeronautics Board (CAB) after the passage of the 1938 Civil Aeronautics Act on the basis of grandfathering: those carriers that were able to show they performed scheduled service prior to the passage of the Act. During the regulated period (1938–1978) these carriers were an especially protected class, with the CAB regulating the industry in many respects in the interests of these companies, a form of regulatory capture. The importance of these carriers is reflected is shown that in 2024, the three largest airlines in the United States, American Airlines, Delta Air Lines and United Airlines were among the carriers certificated through this grandfathering in 1939.
The CAB tightly regulated the industry and categorized airlines by function, the name of the trunk carriers reflected their role, the airlines that flew the main domestic (or trunk) routes. By contrast, a later group of CAB-regulated domestic carriers, first certificated in a five-year period after World War II, were known as local service carriers or feeder carriers, again names reflecting their purpose within the CAB-regulated industry.
The Civil Aeronautics Act of 1938 established a tight regulatory regime for the US airline industry. Airlines were required to be certificated by the Civil Aeronautics Authority (after 1940, this function was inherited by the Civil Aeronautics Board). However, carriers that could show they had engaged in bona fide airline service prior to passage of the 1938 Act were entitled to be grandfathered.[1]
Airline Feeder System[4] | Application rejected | 9 June 1939 | |||||
American Airlines[5] | American Airlines | Still extant 2024 | 9 May 1939 | 2,241.88 | |||
Boston-Maine Airways[6] | Northeast Airlines | Merged into Delta 1972 | 31 May 1939 | 108.47 | |||
Braniff Airways[7] | Braniff International Airways | Collapsed 1982 | 18 July 1939 | 357.72 | |||
Canadian Colonial Airways[8] | Colonial Airlines | Merged into Eastern 1956 | 9 January 1940 | 94.56 | |||
Chicago and Southern Air Lines[9] | Chicago and Southern Air Lines | Merged into Delta 1953 | 17 March 1939 | 215.88 | |||
Condor Air Lines[10] | Application rejected | 8 March 1940 | |||||
Continental Air Lines[11] | Continental Airlines | Merged into United 2012 | 9 March 1939 | 116.44 | |||
Delta Air Lines[12] | Delta Air Lines | Still extant 2024 | 25 February 1939 | 351.65 | |||
Eastern Air Lines[13] | Eastern Air Lines | Collapsed 1991 | 9 June 1939 | 1,678.47 | |||
Inland Air Lines[14] | Inland Air Lines | Merged into Western 1952 | 28 March 1939 | 45.53 | |||
Marquette Airlines[15] | Marquette Airlines | Merged into TWA 1940 | 19 July 1939 | ||||
Mayflower Airlines[16] | Mayflower Airlines | Merged into Northeast 1944 | 31 July 1940 | ||||
Mid-Continent Airlines[17] | Mid-Continent Airlines | Merged into Braniff 1952 | 7 March 1939 | 159.48 | |||
National Airlines[18] | National Airlines | Merged into Pan Am 1980 | 14 March 1939 | 256.30 | |||
Northwest Airlines[19] | Northwest Airlines | Merged into Delta in 2010 | 14 March 1939 | 683.32 | |||
Pennsylvania-Central Airlines[20] | Capital Airlines | Merged into United 1961 | 21 April 1939 | 562.54 | |||
Railway Express Agency[21] | Application rejected | 13 March 1941 | |||||
Transcontinental & Western Air[22] (TWA) | Trans World Airlines (TWA) | Merged into American in 2001 | 16 June 1939 | 1,907.16 | |||
Tri-State Aviation[23] | Tri-State Aviation | Certification revoked 1943 | 31 July 1940 | ||||
United Air Lines[24] | United Airlines | Still extant 2024 | 22 May 1939 | 1,843.73 | |||
Western Air Express[25] | Western Airlines | Merged into Delta 1987 | 7 April 1939 | 195.95 | |||
Wilmington-Catalina Airline[26] | Catalina Air Transport | Ceased operation 1942 | 13 October 1939 | + align="bottom" style="caption-side: bottom; text-align: left;" | (1) ASM = Available seat mile: one passenger seat, available for sale, flown one mile. A flight with 150 seats flown 2000 miles generates 150×2000 = 300,000 ASMs |
Between 1939 and 1941, the CAA/CAB considered 23 grandfather applications by US domestic airlines, as reflected in the CAA/CAB Reports in which CAA/CAB decisions were recorded.[27] [28] Of these applicants, three were denied. Two of these, Airline Feeder System (an east coast airline)[29] and Condor Air Lines (in the San Francisco Bay Area)[30] were denied on the basis of service interruptions and financial weakness. Another applicant, Railway Express Agency, was not an operating airline, but rather a freight forwarder who worked with airlines, and the CAB saw no reason it should be certificated.[31]
Two grandfather applicants received certification but failed to launch certificated service:
Two grandfathered carriers had brief existences as certificated carriers.
See main article: Marquette Airlines. Marquette Airlines was certificated to fly from St Louis to Detroit but outsourced its operation to TWA (which at that time stood for Transcontinental & Western Air) in August 1940, and then sold out completely to TWA in December.[34]
See main article: Wilmington-Catalina Airline. Wilmington-Catalina Airline was founded by the Wrigley family in 1931 and flew two small amphibious aircraft from the Port of Los Angeles to Santa Catalina Island. 1941 plans for expansion using land-based aircraft were ended by the start of World War II, which forced the airline to cease operation in 1942. The company never resumed airline operations of its own, though it contracted with United Air Lines to operate on its behalf 1946–1954.
The 16 grandfathered carriers that continued to operate were the trunk carriers or trunk airlines or trunk lines or trunks.[35] [36] Note the category encompassed airlines that were originally strikingly different in size. In 1948, American was well over 20 times the size of Colonial by ASMs, as Table 1 shows.
As Table 1 also shows, six (Capital, Chicago & Southern, Colonial, Inland, Mid-Continent, Northeast) of the 16 trunk carriers merged out of existence during the regulated period, 1938–1978, leaving 10 trunks as US airline deregulation dawned in 1979: American, Braniff, Continental, Delta, Eastern, National, Northwest, TWA, United and Western.
The CAB saw the trunks as a special category of airline to be particularly protected:
Over time, local service carriers did come to compete with trunk carriers to a degree. In permitting local service carriers to enter some trunk routes, the CAB was motivated in significant part by a desire reduce government subsidy paid to local service carriers, a process known as “route strengthening.”
Further, some local service carrier routes were assigned to trunks. For instance, in 1950, some of the routes originally awarded to Parks Air Lines, a local service carrier, were handed to Mid-Continent Airlines, a trunk airline, after Parks failed to start operation in a timely manner.[37] And in 1955, the CAB also permitted a merger between a trunk airline and a local service carrier, when Continental Air Lines bought Pioneer Air Lines.[38] So the division between local service carriers and trunks was far from absolute.
However, as Table 2 below shows, the distinction between trunk airline and local service airline remained meaningful even in 1978, the last year of the regulated era. Relative to local service carriers, even the smallest trunk airlines flew substantially greater seat-miles and distances and with substantially larger aircraft.
It’s worth considering what airlines were not trunks. What mattered was flying domestic routes in 1938, where “domestic” was the continental United States, since until 1959, Hawaii and Alaska were territories, not states. Pan Am was not a trunk carrier, because as of 1938 it did not fly domestic service. A number of other carriers were certificated to fly routes outside the continental United States by the CAB, such as Panagra and Trans Caribbean, none of these counted as trunks either.
Similarly, there were carriers certificated as, originally, territorial carriers, such as Hawaiian Airlines and Caribair in Puerto Rico.[2]
American Airlines | trunk | 2,736.4 | 45.49 | 154.2 | 799.8 | |||||||||
Braniff Airways | trunk | 966.5 | 17.84 | 138.5 | 583.1 | |||||||||
Continental Air Lines | trunk | 772.0 | 14.53 | 155.2 | 618.5 | |||||||||
Delta Air Lines | trunk | 2,241.6 | 37.55 | 151.5 | 457.9 | |||||||||
Eastern Air Lines | trunk | 2,379.6 | 39.06 | 135.5 | 509.1 | |||||||||
National Airlines | trunk | 636.4 | 13.83 | 174.1 | 694.5 | |||||||||
Northwest Airlines | trunk | 794.4 | 14.30 | 226.2 | 667.2 | |||||||||
Trans World Airlines | trunk | 2,474.7 | 42.65 | 165.0 | 897.1 | |||||||||
United Air Lines | trunk | 3,523.4 | 61.94 | 161.2 | 694.8 | |||||||||
Western Air Lines | trunk | 834.5 | 15.76 | 147.9 | 645.6 | |||||||||
Allegheny Airlines | local svc | 566.8 | 6.72 | 90.4 | 242.5 | |||||||||
Frontier Airlines | local svc | 287.2 | 3.77 | 81.6 | 230.2 | |||||||||
Hughes Air Corp dba Hughes Airwest | local svc | 313.2 | 4.18 | 94.6 | 282.0 | |||||||||
North Central Airlines | local svc | 298.5 | 3.09 | 90.0 | 147.6 | |||||||||
Ozark Air Lines | local svc | 229.7 | 2.70 | 87.3 | 195.9 | |||||||||
Piedmont Airlines | local svc | 205.6 | 2.62 | 85.7 | 180.7 | |||||||||
Southern Airways | local svc | 188.5 | 2.45 | 76.0 | 206.5 | |||||||||
Texas International Airlines | local svc | 181.7 | 2.60 | 90.8 | 304.5 | + align="bottom" style="caption-side: bottom; text-align: left;" | (1) USD mm | + align="bottom" style="caption-side: bottom; text-align: left;" | (2) Available Seat Miles: an ASM is one seat available for sale flown one mile | + align="bottom" style="caption-side: bottom; text-align: left;" | (3) Average seats per flight weighted by miles flown | + align="bottom" style="caption-side: bottom; text-align: left;" | (4) Average flight distance |
Thirteen of the original 19 passenger grandfather certificates from the 1938 Act are still represented in the industry as of 2024.
Six of the grandfather certificates were merged into Delta over time (as well as Delta's own grandfather certificate):
Two of the grandfather certificates were merged into American over time (as well as American's own grandfather certificate):
Two of the grandfather certificates were merged into United over time (as well as United's own grandfather certificate):