Aerospace and defense is one of the few sectors where the investment logic is shaped as much by sovereign budgets and multi-decade program cycles as by quarterly demand. Commercial aircraft orders are placed years before delivery, defense contracts can run for thirty years, and the supplier base is so specialized that entry barriers rival those of any industry in the market. For a long-horizon investor, understanding how this sector is actually structured matters more than tracking any single headline contract.
The three core subsectors
The sector splits cleanly into three functional groups. Commercial aerospace covers the manufacture of passenger and cargo aircraft, engines, and the vast network of component suppliers feeding Boeing and Airbus. Defense primes build weapons systems, platforms, and services for governments, dominated in the US by Lockheed Martin, RTX, Northrop Grumman, General Dynamics, and L3Harris. A third group, often underappreciated, is the aftermarket and services layer: maintenance, repair, overhaul, spare parts, and software-enabled upgrades that generate recurring revenue long after a plane or missile system has been delivered. Aftermarket work has historically carried gross margins well above original equipment sales, which is why aircraft engine makers like GE Aerospace and Rolls-Royce have increasingly priced engines near cost and recovered profit through decades of servicing contracts instead.
The commercial duopoly and its fragility
Commercial aerospace is structurally a duopoly. Boeing and Airbus together account for the overwhelming majority of narrow-body and wide-body aircraft production worldwide, a concentration that has persisted since the 1997 Boeing-McDonnell Douglas merger removed the last meaningful US competitor. This duopoly has historically been associated with pricing discipline and multi-year order backlogs that function as a visible demand runway, but it has also proven fragile in execution. The 737 MAX grounding that began in March 2019 and the subsequent supply chain disruptions through 2020-2023 demonstrated how a single program failure can compress margins and delivery schedules for years. Investors analyzing this subsector tend to watch book-to-bill ratios, backlog-to-revenue multiples, and delivery cadence rather than order announcements alone, since an order is a promise while a delivery is recognized revenue.
Defense budgets as the demand driver
Defense spending behaves differently from almost any other corporate revenue source because its customer is sovereign and its demand is driven by geopolitical risk assessment rather than price sensitivity. US defense outlays reached roughly 886 billion dollars in fiscal 2024 appropriations, and NATO members outside the US have collectively increased spending in response to the European security environment that shifted after February 2022. This has historically made defense primes a counter-cyclical allocation relative to consumer-facing sectors, since defense budgets tend to rise during periods of geopolitical stress that often coincide with broader market drawdowns. The analytical framework here centers on multi-year program backlogs, which for the largest primes often extend three to five years of visible revenue, and on the distinction between cost-plus contracts, where margin is contractually protected, and fixed-price contracts, which transfer execution risk to the contractor.
Supply chain concentration and single points of failure
Beneath the primes and airframers sits a supplier base with alarming concentration at certain nodes. Titanium forgings, specialty castings, and certain avionics components often trace back to a small number of qualified suppliers, a dynamic that became visible during the 2020-2022 period when supply shortages extended aircraft delivery timelines well beyond original schedules. This concentration exists because aerospace certification processes, governed by bodies like the FAA and EASA, can take years and cost tens of millions of dollars, making it commercially unattractive for new entrants to qualify alternative sources. For investors, this means the sector's resilience is partly a function of how diversified a given supplier's customer base is across both commercial and defense programs, since a company serving only one end market carries concentrated cyclical exposure.
Space as the emerging fourth subsector
Space-related revenue, once a rounding error within diversified defense primes, has become a distinct subsector as launch costs have fallen. The cost per kilogram to low Earth orbit has declined from several thousand dollars in the space shuttle era to figures frequently cited below 2,000 dollars with reusable launch vehicles, a shift that has expanded the addressable market for satellite communications, earth observation, and government space programs. This subsector carries a different risk profile than traditional defense work, blending venture-style technology risk with government contract stability, and it has historically attracted capital allocation discussions distinct from the rest of the sector.
Reading the cycle correctly
The practical skill in this sector is distinguishing a commercial aerospace cycle, which tracks global air travel demand and airline fleet renewal, from a defense cycle, which tracks government budget appropriations and threat perception. The two cycles are only loosely correlated, which is part of why diversified aerospace and defense conglomerates have historically exhibited lower earnings volatility than pure-play commercial aerospace suppliers. Global air traffic, measured in revenue passenger kilometers, surpassed pre-pandemic 2019 levels globally by 2024 according to IATA data, while defense budgets across NATO have risen independently of that recovery. Treating the sector as a single monolithic bet obscures this divergence.
The rule to internalise
Aerospace and defense rewards investors who separate the sector into its structural components before forming any view: commercial duopoly economics, sovereign-funded defense cycles, high-margin aftermarket services, concentrated supply chains, and an emerging space subsector each respond to different drivers and different risks. The backlog is the single most informative number in the sector, but it must be read alongside delivery execution, contract type, and customer concentration rather than taken as a standalone signal of future revenue.
Educational content only. Not investment advice.