Logistics in Confined Spaces in Naval Aviation and Maintenance Engineering on Aircraft Carriers: The Process of Returning to Operational Service from the F-4 to the F-35

The success of aircraft carrier operations depends on the ability to continuously generate maximum combat power within a confined space. The confined spaces on the flight deck, combined with dynamic and hazardous operations and challenging sea conditions, necessitate the minimisation of aircraft Turnaround Times (TAT). The Sortie Generation Rate (SGR), the key metric determining an aircraft carrier’s combat capability, is directly shaped by the speed of line maintenance, the coordination of parts supply, and the deck layout architecture. Whilst approximately 120 sorties can be generated in a 12-hour operational day on traditional Nimitz-class aircraft carriers, the target for modern Gerald R. Ford-class (CVN 21) ships is to increase this to 160 sorties per day, and to 270 sorties over a 24-hour period under intense combat conditions. Supporting an increase on this scale requires the optimisation of logistics processes and aircraft maintenance engineering through mathematical operations research models and lean process integration.

Cover photo: USS Enterprise (CVN 65) at sea (6 November 1998). An F-14B ‘Tomcat’ aircraft belonging to Fighter Squadron 32 (VF-32) is checking whether the landing gear is functioning properly. The USS Enterprise was deployed to the Persian Gulf. Photo: US Navy / Nicholas D. Sherrouse

Spatial Constraints and Layout Factors in Aircraft Carrier Operations

All activities on the flight deck—such as aircraft movement, refuelling, munitions loading and line maintenance—are processes carried out simultaneously within a confined space, requiring the precision of a ‘ballet’. On a Nimitz-class aircraft carrier, there is typically only space for 30 to 40 aircraft on the flight deck. Under these spatial constraints, the area occupied by each aircraft on the deck and its manoeuvrability have been standardised as the ‘Spotting Factor’.

The Spotting Factor is directly related to the aircraft’s geometric dimensions and, in particular, the efficiency of its wing folding mechanisms. One of the most challenging engineering steps in adapting a land-based aircraft to aircraft carrier conditions is minimising the Spotting Factor by equipping the aircraft with a foldable wing structure. In modern naval aviation, the F/A-18 Hornet and Super Hornet platforms are considered the benchmark with a layout factor of 1.0; whereas older or larger platforms such as the F-14 Tomcat, A-3 Skywarrior and RA-5C Vigilante have layout factors approaching 2.0. A high space factor necessitates the movement of more aircraft on the flight deck, thereby increasing towing operations carried out by tractors and directly extending cumulative turnaround times (TAT).

Wing folding mechanisms and fuselage strength to absorb aircraft carrier landing loads increase the aircraft’s structural weight whilst also introducing maintenance complexity. To enable an aircraft to withstand aircraft carrier catapult launches (cat shot) and arrested landings (trap), the distribution of loads from the launch bar and tail hook (tail hook) loads must be distributed, and the aircraft’s landing gear must be designed to withstand vertical descent rates of 12–15 feet per second (30–35 feet in extreme cases). This structural requirement significantly increases the maintenance man-hours per flight hour (MMH/FH) compared to land-based aircraft.

MMH/FH is one of the most important efficiency/maintenance indicators in aviation and logistics, showing how many hours of maintenance manpower are required on the ground for every 1 hour an aircraft spends in the air.

As ship-based aircraft suffer greater wear and tear due to salt water, humidity and hard landings, this ratio is much higher than for land-based aircraft.

An F-4B Phantom II belonging to the US Navy’s VF-111 is being repainted on the aircraft carrier USS Coral Sea (CVA-43), It was assigned to Carrier Air Wing 15 (CVW-15) aboard the Coral Sea for deployment to the Western Pacific and Vietnam between 12 November 1971 and 17 July 1972. Photo: US Navy

Comparative Platform Analysis: F-4, F-14, F-18 and F-35C

The logistical and maintenance engineering requirements of different generations of combat aircraft that have served and are currently serving on aircraft carriers clearly demonstrate the development process of aviation technology and the importance of a design philosophy focused on ease of maintenance.

F-4 Phantom II: Hydraulic and Materials Engineering Limitations

As a third-generation fighter-bomber, the F-4 Phantom II imposed a very heavy workload in terms of logistics and maintenance engineering. Towards the end of its service life, it demanded an extraordinarily high workload of approximately 187 maintenance man-hours per flight hour (MMH/FH). One of the major maintenance bottlenecks on the F-4 platform was the hydraulic systems. The aircraft featured three independent hydraulic systems operating at 3,000 psi: Power Control 1 (PC-1), Power Control 2 (PC-2) and Utility. The piping, valves and seals of these systems required constant leak testing after each flight and frequent component replacements.

Furthermore, aircraft produced during the F-4 era made extensive use of carcinogenic asbestos materials in engine blankets, hydraulic clamps, brake linings and hot air ducts. This situation made it mandatory for maintenance personnel to work with protective equipment, slowed down component replacement processes and caused significant delays in turnaround times within the hangar. The F-4’s pneumatic starting system, being dependent on external starting trolleys (start carts), also contributed to the clutter of equipment on the flight deck.

F-14 Tomcat: Variable-Geometry Wings and Mechanical Complexity

The fourth-generation air defence fighter, the F-14 Tomcat, is one of the most maintenance-intensive aircraft in aviation history. Throughout its operational life, the F-14 required an average of 40 to 60 (and according to some sources, over 50) maintenance man-hours per flight hour. The primary reason for this high workload was the variable-geometry (Variable-Geometry / Swing-Wing) wing design, which provided the aircraft with unique aerodynamic advantages but was mechanically extremely complex. The wing sweep mechanism, titanium wing box and movable wing vanes alone accounted for a maintenance workload of approximately 60 man-hours per flight hour.

Furthermore, the Pratt & Whitney TF30 engines used on the F-14A variant were incompatible with the aircraft’s fuselage and were highly prone to compressor stall at high angles of attack and during sudden throttle movements. This led to frequent engine damage, turbine blade fractures and unscheduled engine replacements. The F-14’s hydraulic leaks were so chronic that a joke circulated among technical personnel: “If the Tomcat isn’t leaking hydraulics, there’s no hydraulics left in it.” The difficulty in accessing maintenance panels and the lack of modular systems meant that fixing a single fault required dismantling half the aircraft, creating a significant risk of the aircraft becoming a ‘Hangar Queen’ on the hangar deck.

F/A-18 Hornet and Super Hornet: Easy Maintenance and the LRU Concept

The F/A-18 Hornet represents a paradigm shift in naval aviation maintenance engineering. Taking into account the lack of maintenance space on the aircraft carrier and the difficulty of towing the aircraft into the hangar, all of the F/A-18’s avionics and critical subsystems were designed as “Line-Replaceable Units” (LRUs) that could be quickly removed and fitted on the flight deck. Whilst classic F/A-18C/D models required approximately 16 to 20 MMH/FH per flight hour, this figure has been reduced to 10 to 15 (or approximately 12) MMH/FH in the more modern F/A-18E/F Super Hornet models, which are 25% larger in fuselage size.

- Line-Replaceable Units (LRU): In the event of a fault on the aircraft, rather than dismantling the entire system or spending hours repairing it in the hangar, these are modular components that can be replaced with a new one in a matter of minutes on the flight line (on the runway or deck) simply by unscrewing the bolts and sockets, following a ‘plug-and-play’ (plug-and-play) principle, the faulty unit can be replaced with a new one in a matter of minutes (for example, a faulty radio unit, radar module or flight computer).

-MMH/FH (Maintenance Man-Hours per Flight Hour): A performance ratio indicating the number of man-hours of maintenance required on the ground for every 1 hour of flight time an aircraft spends in the air. For example, a value of 12 MMH/FH means that after the aircraft has flown for 1 hour, the technical team must carry out maintenance and checks for 12 hours (as the sum of total working hours). The lower this figure, the less maintenance the aircraft requires and the quicker it is ready to fly again.

The greatest challenge arising from the long-term use of the F/A-18 series is the metal fatigue caused on the airframe by catapult launches and arrested landings. To extend the service life of these aircraft, which originally had a fuselage life of 6,000 flight hours, to 8,000 and even 10,000 flight hours, the Service Life Assessment Programme (SLAP) and the Service Life Extension Programme (SLEP) have been implemented. The High Flight Hour (HFH) inspections carried out as part of this programme increased the number of critical ‘hot spots’ examined from 83 to 128 and doubled the inspection duration (from 1,200 to 2,400 man-hours). Nevertheless, the Super Hornet has formed the backbone of aircraft carriers for many years thanks to its high reliability and low maintenance requirements.

F-35C Lightning II: 5th Generation Complexity and Stealth Maintenance

The F-35C is a 5th generation low-observable (stealth) fighter aircraft, specifically designed for the US Navy, featuring folding wings and reinforced landing gear. The most notable difference in the F-35C’s maintenance engineering lies in the protection of the special radar-absorbing coatings (Radar Absorbent Material – RAM) and composite surfaces used to keep the aircraft’s radar cross-section (RCS) low. Whenever a panel is removed or a microscopic scratch forms on the fuselage, the coating must be renewed and cured using specialised processes.

According to official Joint Programme Office (JPO) data, the F-35C’s actual maintenance workload stands at 7.55 man-hours per flight hour (MMH/FH) (4.79 for the F-35A; 7.48 for the F-35B). Although some independent analyses and budget reports [particularly data from the Congressional Budget Office (CBO)] estimate this figure to be around 13 hours due to the aircraft’s complexity, the maintenance times for a fifth-generation aircraft are, in any case, significantly lower than those of older systems such as the F-14 and F-4. However, the F-35C’s flight-hour costs (approximately $34,000 to $42,000) and spare parts bottlenecks in the global supply chain continue to pose the greatest logistical challenges.

28 January 2007 An F/A-18 Super Hornet is seen in the hangar of the Nimitz-class aircraft carrier USS Ronald Reagan (CVN-76). Photo: US Navy, John P Curtis

Table 1: Maintenance Man-Hours (MMH/FH), Spotting Factors and Chronic Structural Issues of US Navy Aircraft Over Time

Platform Generation Spotting Factor (Spotting Factor) Maintenance Man-Hours (MMH/FH) Fundamental Structural and Mechanical Limitations Degree of Corrosion Sensitivity

F-4 Phantom II 3rd Generation ~1.2 – 1.4 ~20 – 90 (187 towards the end of its service life) Leaks in three independent hydraulic systems, asbestos-containing insulation materials High (Old alloys, inadequate sealing)

F-14 Tomcat 4th Generation ~1.8 – 2.0 ~40 – 60 Variable-geometry wing mechanism, TF30 engine compressor finish Very High (Complex hinges, titanium-steel joints)

F/A-18C/D Hornet 4th Generation 1.0 ~16–20 Catapult and arresting gear fatigue, vertical tail corrosion Medium (Advanced alloys, drainage holes)

F/A-18E/F Super Hornet 4.5th Generation 1.0 ~10–15 (Actual ~12) Airframe life extension (SLM) fatigue cracks, high landing impact loads 1 Medium–Low (Structure with increased composite density)

F-35C Lightning II 5th Generation ~1.1–1.2 ~7.55 (Theoretical/Target: 9.0) RAM coating protection, high thermal loads from tightly integrated avionics Low–Medium (High composite content but RAM degradation in salt water)

F Detailed operating and support costs derived from the F-35A variant serve as a key reference for understanding the logistics budget of a 5th-generation fighter aircraft. Whilst maintenance activities account for the largest share of total costs at 40–45 per cent, contractor logistics support (CLS) -CLS) and personnel costs are also significant items.

Table 2: Actual Operating Cost Components and Budget Breakdown per Flight Hour for F-35A Aircraft

Cost Component Approximate Hourly Cost ($) Share of Total Cost (%)

Scheduled and Unscheduled Maintenance ~15,000 – 18,000 ~(40 – 45)

Contractor Logistics Support (CLS) ~5,000 – 7,000 ~% (13 – 17)

Fuel (JP-8 / JP-5 Equivalent) ~4,480 ~% (11 – 13)

Personnel (Pilot, Technician, Support) ~4,000 – 6,000 ~% (10 – 14)

Spare Parts and Consumables ~3,000 – 5,000 ~% (8 – 12)

Depreciation and Programme Expenses ~2,000 – 3,000 ~% (5 – 7)

TOTAL (Estimated) ~34,000 – 42,000 % 100

Corrosion Dynamics and Material Protection in the Marine Environment

The open sea environment is one of the most aggressive environments, triggering electrochemical corrosion reactions on metal surfaces due to its high relative humidity, chloride ions (salt) and temperature fluctuations. This situation, which threatens the structural integrity of aircraft, is one of the main causes of unplanned maintenance and consequently (TAT).

Structural Areas Susceptible to Corrosion

In maritime aviation aircraft, the areas most affected by corrosion are classified as follows based on microscopic examinations and field experience:

-Outer Fuselage and Joints: Rivet joints on the wings, tail and fuselage, panel joints and galvanic corrosion zones where different metals come into contact. Moisture and contaminants seep through these hairline cracks, damaging the protective coatings. Antenna mounting points and wheel wells are particularly susceptible to such ingress. In aluminium alloys, corrosion manifests as a greyish-white powdering and blistering, whilst in iron-containing metals, reddish rust deposits are observed.

-Exposed Fasteners: The hydraulic brackets of landing gear under dynamic load, engine mounting components, vertical tail connections and horizontal stabiliser hinges are the points where protective primers and mastic coatings wear away most rapidly.

-Areas Prone to Friction Corrosion: The corrosion process accelerates in areas subjected to high pressure, inertial forces and mechanical friction, such as wing spars, wing access panels, flap rails and lap joints.

-Discharge and Exhaust Areas: In areas where corrosive vapours and gases are emitted—such as the APU exhaust outlet, air conditioning unit discharges and battery ventilation holes—vapour flow accelerates the corrosion process.

-Internal Fuselage Surfaces: Connection points, drainage holes, and the areas surrounding lavatories and battery compartments within the aircraft are susceptible to corrosion due to accumulated moisture.

Corrosion Prevention and Surface Treatment Technologies

Preventing and addressing corrosion involves multi-step technical processes to be carried out on the flight deck or in the hangar:

-Washing Regulations: Aircraft must be washed regularly using aviation-approved cleaning chemicals and demineralised water to remove salt deposits. Additionally, regular compressor and turbine washing procedures are carried out to prevent high-temperature corrosion (sulfidation) caused by salt ingestion in the engines.

-Surface Cleaning and Chemical Stripping: In areas where corrosion is detected, the dirt and grease layer is first removed. A chemical stripper is applied to remove the paint layer, and the surface is cleaned with brushes. Stubborn residues must be removed using non-metallic scrapers, and the surface must be washed with fresh water at a pressure of 3,000 to 5,000 PSI.

-Corrosion-Inhibiting Coatings: Once the abrasion and cleaning processes are complete, corrosion inhibitors such as ACF-50, which remove moisture and form a protective barrier, are sprayed onto the surface, followed by the application of primer and topcoat.

-Blasting and Sandblasting Restrictions: When performing steel media blasting on tanks or voids beneath the flight deck or hangar, leak-proof barriers and protective enclosures must be used to prevent these hard abrasives from escaping onto the flight deck, lifts or hangar and damaging the aircraft’s sensitive surfaces.

Physical and Digital Logistical Bottlenecks

Optimising turnaround times (TAT) within the limited spaces on an aircraft carrier is not limited to physical work on the aircraft alone. Resolving the bottlenecks created by both physical and digital processes within the ship’s own logistical architecture is of critical importance.

Physical Logistics Bottlenecks and Ammunition Flow

One of the major physical logistics bottlenecks on an aircraft carrier is the transport and loading of ammunition from the magazines to the flight deck. In traditional systems, this process is described using the Hybrid Flow Shop (HFS) model and consists of the following stages:

T(Total) = T(Stage I) + T(Stage II) + T(Stage III) + T(Stage IV)

- Stage I (Weapons Retrieval): This is the process of retrieving munitions from the armoury on the lower deck using bomb chutes and transporting them to the lower-level lifts. Here, there are constraints regarding setup time (T0) and the minimum transport interval (tint) are present.

-Stage II (Weapons Buildup): This is the process of transporting materials vertically at a constant speed from the lower-deck lifts to the hangar deck (TL).

-Stage III (Weapons Assembling): This is the process of assembling munitions in the preparation area on the hangar deck and transporting them to the upper-deck lifts (TKass). In this phase, fluctuations in the assembly team’s performance are simulated using a sigma error margin.

-Phase IV (Weapons Striking Up): The process of raising the prepared munitions to the flight deck via upper-deck lifts (TL).

On Nimitz-class aircraft carriers, the opening of the munitions transport lifts directly onto the centre of the flight deck required flight operations to be suspended during munitions deployment. On the Gerald R. Ford-class carriers, this bottleneck has been overcome with Advanced Weapons Elevators (AWE) featuring Linear Synchronous Motor (LSM) technology. These cable-free elevators offer a 24,000-pound load capacity and a vertical speed of 150 feet per minute, providing a 200% increase in capacity and a 150 per cent in speed compared to older systems, whilst being positioned at the edges of the flight deck to eliminate operational downtime. Furthermore, automated transport prototypes such as the High Rate Vertical to Horizontal Material Movement (HRVHMM) system can transfer loads of up to 6,000 pounds along both horizontal and vertical axes without the need for manual labour. I would like to address this topic in detail by writing an article on munitions transport and aircraft transport lifts. At this point in the article, I can only provide this much information.

Unplanned Maintenance, Cannibalisation and In-Hangar Tests

Severe faults occurring unexpectedly on an aircraft carrier lead to a major logistical crisis due to limited resources. Twists in the aircraft fuselage resulting from hard landings (hard landings) can cause twisting of the aircraft fuselage or hairline cracks in the titanium wing roots; as these require laser alignment tools and factory engineers not available on board, these aircraft are generally beyond repair and are towed to the far corners of the hangar.

This situation triggers a ‘cannibalisation’ (part-stripping) spiral. As it can take weeks for spare parts to reach the ship, generators, avionics, actuators and even engine parts are stripped from inactive aircraft in the hangar and fitted to other aircraft to keep those on the flight line operational. By the end of a six-month deployment, this donor aircraft is virtually a wreck, and getting it back on its feet requires hundreds of extra man-hours.

Another bottleneck within the hangar is engine changes. As performing an engine change on the flight deck paralyses operations, the aircraft is brought into the hangar. Once the new engine is fitted, the engine test (jet run-up) cannot be carried out on the flight deck; instead, the engine is suspended from an external test stand at the stern of the ship and run in and calibrated at midnight (for example, at 02:30). In avionics repairs, the AN/USM-63 Consolidated Automated Support System (CASS) test benches play a critical role. This system, comprising Hybrid (HYB), Radio Frequency (RF), Communication/Navigation (CM) and Electro-Optical (EO) modules, and with 90% hardware commonality, it saves space in the ship’s limited maintenance area. The F/A-18’s targeting pods are tested on this system’s EO3 calibration bench to verify their accuracy.

Digital Logistics Bottlenecks: The ALIS and ODIN Transformation

The greatest bottleneck in the maintenance processes of 5th-generation aircraft such as the F-35C stems not from physical constraints but from the software infrastructure. The Autonomic Logistics Information System (ALIS) was designed as a monolithic software system to manage all aircraft maintenance, supply chain and mission planning processes. However, over time, the system led to major logistical problems. Maintenance personnel were wasting time entering data into the system rather than attending to the aircraft, and due to the numerous false positive error codes generated by the system, aircraft that were actually airworthy were grounded. More importantly, for ALIS to function, a constant, high-bandwidth internet connection to central servers in Texas was required; when the satellite connection was lost over the open sea, the system ceased to work, and even clearing a simple error code became impossible.

Developed to overcome these issues, the Operational Data Integrated Network (ODIN —ODIN) was developed to overcome these challenges and features a cloud-based, modular architecture. The ODIN Base Kit (OBK), which forms the hardware foundation of the ODIN transition, is 75% smaller and lighter (two modules, each weighing under 100 pounds) than the old ALIS SOU-U servers, 30% cheaper, and has 50% faster data processing capacity. Most importantly, the OBK operates with local ‘Edge Computing’ capability in intermittent connectivity environments such as aircraft carriers, enabling all maintenance codes to be resolved locally even without an internet connection and significantly reducing TAT times on the flight line.

TAT Optimisation Using Operations Research and Lean Maintenance Methods

To minimise turnaround times (TAT) in the limited spaces on aircraft carriers, industrial engineering methods, the Theory of Constraints (TOC), Critical Chain Project Management - CCPM) and advanced computer-based operations research simulations are used effectively.

Lean Maintenance and TAT Time Windows

The lean maintenance philosophy treats turnaround times on the aircraft carrier as four overlapping time windows and aims to eliminate waste (non-value-added waiting, transport, and over-processing) in each:

1. Line Maintenance (Line Maintenance / Gate Turnaround TAT): This is the critical period of 45 to 90 minutes from the aircraft landing and being chocked in (block-on) until the engines are started for the next flight (block-off). Any unplanned parts requirement or delay during this phase causes a cumulative delay to the entire flight schedule.
2. Heavy Maintenance and Overhaul (Heavy MRO / Bay TAT): Covers C and D level inspections (C inspection 7–14 days, D inspection 28–60 days). Every additional day the aircraft spends in the hangar, whether on board or at the shipyard, incurs extra logistical costs of between $8,000 and $14,000 per day in operational planning.
3. Defect Management TAT: The time elapsed from the detection of a fault to the approval of a Minimum Equipment List (MEL) deferral (industry average 90 minutes). Paper-based approval mechanisms account for 18–22% of delays; digital workflows can reduce this time to under 25 minutes.
4. Unscheduled Maintenance TAT: 60% of delays stem from unscheduled maintenance. Proactive and predictive maintenance techniques can reduce groundings (AOG) by 45%.

Within the Theory of Constraints (TOC) framework, the system’s bottleneck—such as a shortage of qualified personnel (e.g., a shortage of B1 technicians) or a lack of critical parts—is identified to optimise workforce allocation. The Critical Chain Project Management (CCPM) approach, however, prevents maintenance from starting prematurely before materials reach the aircraft; as keeping an aircraft with missing parts operational leads to an increase in the system’s work-in-progress (WIP) in the system, leading to the fragmentation of resources and cumulative delays.

Algorithmic Modelling and Simulation Studies

Advanced operations research methods utilise mathematical models and computer simulations to optimise flight deck layout and take-off operations.

-Spotting Allocation using Genetic Algorithms: The allocation of parking spots on the flight deck to minimise the taxiing distance and time of landing aircraft to the catapults is carried out using Genetic Algorithm (GA)-based models to minimise the taxi distance and time for landing aircraft to reach the catapults. Using pseudospectral methods, aircraft taxi routes and access times to the catapults are calculated, and an optimal flight deck layout plan that minimises the risk of collision is dynamically generated. These processes, which traditionally rely on human experience and manual template boards known as ‘Ouija Boards’, are being digitised using computer-aided systems such as the Aviation Data Management and Control System (ADMACS).

-LTA-HPSO + AAE-SAC Two-Stage Optimisation Framework: Aircraft take-off scheduling on the flight deck is subject to numerous spatial and temporal constraints due to limited space. The two-stage model developed to optimise this complex process is as follows:

-Stage 1 (AAE-SAC): A Deep Reinforcement Learning (DRL)-based algorithm is used to solve collision-free path planning for aircraft on the deck under dynamic constraints.

-Stage 2 (LTA-HPSO): A Particle Swarm Optimisation algorithm, developed to optimise the take-off sequence and catapult pairings of the aircraft, is applied. According to simulation results, in a highly congested take-off scenario involving 24 aircraft, this integrated model reached a solution in an average of just 185.19 seconds, reducing the total operation time by 26.18% compared to traditional PSO+Heuristic models and by 49.54% compared to PSO+SAC models.

-Agent-Based Modelling and Optimal Manning Levels: The OMS (Optimal Manning Simulation) and PMASCS (Personnel Multi-Agent Safety and Control Simulation) software, developed to determine the optimal number of personnel to work on the flight deck, model the ammunition handlers, chockers, fuelers and maintenance crews on the deck as independent agents. Simulation studies have shown that three is the optimal number of maintenance crew members to be deployed on the flight deck; exceeding this number does not reduce take-off times due to other bottlenecks, such as the installation of the holdback bar on the catapult, but merely increases congestion on the deck and the risk of personnel collisions.

Furthermore, research has shown that human decisions and experience-based heuristics often produce safer and more protective plans than pure optimisation algorithms, although the algorithms do yield more aggressive time savings.

The Impact of Dock Maintenance Cycles on Operational Readiness

The duration of aircraft carriers’ dock maintenance (depot maintenance) and deployment cycles directly affect the ship’s duration of presence in open waters and its capacity to be deployed in emergencies (surge). Research conducted by the RAND Corporation has highlighted the effects of different maintenance and deployment cycles on operational readiness.

Table 3: The Effects of Different Operational Cycle Models on Fleet Deployment Timing and Readiness Rates

Cycle Type (Months) Deployment Duration (%) Readiness for Deployment Within 30 Days (Surge) (%) Readiness for Deployment Within 30–90 Days (%) Time Spent in Depot Maintenance (%)

32-Month Standard Cycle 19% 46% 11% 24%

18-Month Short Cycle 31% 15% 18% 36%

42-Month Long Cycle 29% 44% 9% 18%

In the current 32-month standard cycle, ships are deployed once, whilst the 42-month cycle encompasses two six-month deployments and best contributes to the US Navy’s objective of maintaining at least six ships ready at any given time (‘6+1 fleet’). However, whether the necessary shipyard maintenance can be completed on time in this long cycle remains a technical question mark. Whilst shipyards have a monthly workforce capacity of approximately 30,000 man-days, the shorter 18-month cycles help balance the shipyard workload by reducing the size of work packages.

The most important parameter for measuring the overall readiness level of an aircraft carrier is the Fully Mission Capable (FMC) rate. The primary factors reducing the FMC rates of deployed air fleets are: parts requests taking longer than two days to fulfil, high cannibalisation rates, and unplanned flight hours.

The mission capability rates for selected military air platforms for the 2024 financial year and historical data provide an overview of the challenges in maintenance engineering:

Table 4: Combat Readiness Levels by Air Platform Type and Supply Chain/Maintenance-Related Bottlenecks

Platform Type Role Mission Capability Rate (MCR - % / Period) Key Logistical Constraints

F-22 Raptor Air Superiority 40.19% (FY24) Spare parts shortage, high airframe complexity

F-35A Lightning II Multi-Role Combat 51.50% (FY24) Parts supply issues, global CLS bottlenecks

F-35A (Historical) Multi-Role Fighter 55.00% (2017) ALIS software bugs and early production blocks

C-5M Galaxy Strategic Transport 48.60% (FY24) Vanishing vendor syndrome

CV-22 Osprey Tiltrotor Transport 30.45% (FY24) Flight suspension decisions due to safety concerns

E-8C JSTARS ISR / Command 64.00% (2017) Ageing airframe and obsolescence of avionics

T-1A Jayhawk Training 56.00% (2017) Bureaucratic delays in the supply of civilian-derived parts

FY24 is an abbreviation for the English financial term ‘Fiscal Year 2024’ and translates to ‘2024 Financial Year’ in Turkish.

Results and Strategic Maintenance Engineering Roadmap

Optimising turnaround times (TAT) in naval aviation within highly constrained and corrosive environments, such as on aircraft carriers, requires the integration of multidisciplinary engineering solutions. The strategic roadmap developed in light of analyses and mathematical modelling should be built upon the following key pillars:

Firstly, the architecture of avionics maintenance and logistics management systems must be freed from monolithic structures. The ALIS experience on the F-35C platform has demonstrated that internet-dependent centralised systems pose a significant risk factor in open-sea operations. Modular systems with ‘Edge Computing’ capabilities—such as the ODIN Base Kit (OBK) hardware deployed under the ODIN project—which are independent of central servers and capable of operating offline, should be widely adopted. This will ensure that fault codes can be processed locally even in the absence of an internet connection on the flight deck or in the hangar, thereby reducing TAT times.

Secondly, the physical flow of materials on the flight deck must be supported by electromagnetic and automated systems. Advanced Weapon Elevators (AWE) and automated horizontal-vertical material handling systems (HRVHMM), successfully implemented on the Gerald R. Ford class, completely eliminate bottlenecks in the ammunition supply chain. These layouts, which do not block the centre of the flight deck, allow for the safe transport of ammunition whilst flight operations continue and dramatically reduce the time aircraft spend waiting on the deck.

Thirdly, artificial intelligence and operational models that go beyond human intuition should be utilised in aircraft positioning and take-off planning on the deck. Models combining deep reinforcement learning and particle swarm optimisation, such as the two-stage LTA-HPSO + AAE-SAC algorithm framework, should be integrated into decision support systems (ADMACS, etc.). This would enable jet blast, taxiway conflicts and take-off sequencing on the deck to be resolved within seconds, thereby halving total take-off operation times. Furthermore, as demonstrated by PMASCS factor-based modelling, optimal manning levels (OMS) that limit human density on the deck must be rigorously applied.

Finally, corrosion damage caused by the aggressive marine environment must be prevented using proactive and predictive methods. Non-destructive testing methods such as Eddy Current should be applied regularly to sensitive areas such as vertical tail hinges, wing spars and landing gear bays; environmental safety (e.g. steel scraping barriers) must be ensured during chemical stripping processes, and post-cleaning corrosion-inhibiting misting technologies such as ACF-50 should be made a standard maintenance step. Conducting processes in parallel (parallel maintenance, fuel and ammunition loading), preparing ready-to-use material kits in advance, and utilising digital work cards will minimise delays caused by unscheduled maintenance, thereby maximising the sortie production rate.

Our Naval Aviation series will continue.

Reading the first four articles that form the foundation of our Naval Aviation series will enable you to understand the technical details and doctrinal background in this article much more clearly. I have provided the link to the relevant publications below for your reference.

Take-off and Landing Configurations on Naval Aviation Platforms: CATOBAR, STOBAR and STOVL

https://strasam.org/savunma/deniz-silah-ve-sistemleri/deniz-havaciligi-platformlarinda-inis-kalkis-konfigurasyonlari-catobar-stobar-ve-stovl-4160

The Evolution of US Navy Jets from an Engine Architecture Perspective

https://strasam.org/savunma/deniz-silah-ve-sistemleri/motor-mimarisi-perspektifinden-abd-donanma-jetlerinin-evrimi-4166

Structural and Technical Evolution of US Navy Aircraft Carrier Aircraft: 1945–1965

https://strasam.org/savunma/deniz-silah-ve-sistemleri/abd-donanmasi-ucak-gemisi-ucaklarinda-yapisal-ve-teknik-evrim-19451965-4168

Structural and Technical Evolution of US Navy Aircraft Carrier Aircraft: 1965–2025

https://strasam.org/savunma/deniz-silah-ve-sistemleri/abd-donanmasi-ucak-gemisi-ucaklarinda-yapisal-ve-teknik-evrim-19652025-4172

References

1. Flight Deck Safety and Operations Guide - Scribd, , https://www.scribd.com/document/706609890/Flight-Deck-Awareness-V2
2. A Naval Safety Center Publication, , https://www.airpac.navy.mil/Portals/53/Flight%20Deck%20Awareness%20V2.pdf?ver=8Q-OX6US7j7RRdAPMUMySg%3D%3D
3. Modelling efficiency and safety on an aircraft carrier flight deck - IDEAS/RePEc, , https://ideas.repec.org/a/sae/joudef/v21y2024i4p441-452.html
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50. Here’s a handy inventory list of USAF aircraft and their mission capability rates, , https://www.twz.com/19119/heres-a-handy-inventory-list-of-usaf-aircraft-and-their-mission-capable-rates
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