Overview
The definition of a fifth-generation fighter includes more than stealth; sensor fusion and data sharing are central features. Stealth is achieved by reducing radar detectability, masking infrared and visual signatures, and minimizing radio emissions.
EOTS, TFLIR and DAS
The first system demonstrated by test pilots is the electro-optical targeting system (EOTS), one of the most important sensors alongside the AN/APG-81 active electronically scanned array (AESA) radar. EOTS comprises two subsystems: targeting forward-looking infrared (TFLIR) and the distributed aperture system (DAS). On official sources from Lockheed Martin, Northrop Grumman and F-35 documentation, EOTS and DAS are described as separate systems; TFLIR is one of the cameras used by EOTS (others include CCD-TV cameras and a laser). The systems are designated AAQ-40 for EOTS and AAQ-37 for DAS. Together with the APG-81 radar, they enable the pilot to locate, track and designate airborne, ground vehicles or other targets day or night and in all weather conditions.
EOTS, or the TFLIR mentioned in video demonstrations, is functionally equivalent to the external targeting pods carried on legacy fighters. In the F-35, the system was developed from the Sniper XR targeting pod and integrated into the fuselage by Lockheed Martin. The compact installation under the nose reduces radar cross section (RCS) and drag. The pilot can use it for visual target acquisition and autonomous weapon employment in laser designation mode, and it can also detect other aircraft or units on the ground by tracking laser spots. Lockheed Martin has stated that an advanced EOTS variant is planned for Block 4 development, with enhancements including shortwave infrared, high-definition television, infrared markers and improved detector resolution to extend pilot detection and identification ranges and overall targeting performance.
Threats from Low-Observable Adversaries
Although the F-35 and other stealth aircraft have low or minimal radar cross section, they still emit infrared signatures. This makes them vulnerable to small, fast non-stealthy aircraft that employ low-observable coatings, refrain from radio communications and radar emissions (minimizing electromagnetic radiation), and use their ISR sensors, high-speed computation and interferometry to geolocate adversary radar and evade detection.
Distributed Aperture System (DAS)
The distributed aperture system is an innovative subsystem consisting of six sensors arrayed around the aircraft to provide 360-degree coverage. Images from DAS are projected onto the helmet visor, enabling the pilot to effectively see through portions of the airframe. Designed and manufactured by Northrop Grumman, DAS performs missile approach warning, infrared search and track (IRST) and navigation forward-looking infrared (NAV-FLIR) functions. In practical terms, the system alerts the pilot to approaching aircraft and missile threats, provides day/night imagery and adds target designation and fire-control capabilities. During testing, DAS demonstrated the ability to detect, track and designate rapidly successive ballistic missile launches and to detect and geo-locate tank firing during live-fire exercises. DAS is also undergoing upgrades to further extend its capabilities.
Helmet-Mounted Display
The current-generation helmet is integrated with the aircraft and functions as an additional sensor for the pilot. Two projectors generate images shown on the inner visor, which can include DAS imagery, flight-critical information (speed, heading, altitude), tactical data (targets, friendly aircraft, navigation waypoints) and night-vision imagery. One of the major innovations of this helmet is the ability to use night vision without losing the overlaid symbols and image system. Previously, pilots had to choose between NVGs (night vision goggles) and helmet-mounted cueing systems because NVGs sit close to the eyes and interfere with visor projection. Only a few helmet systems support both night vision and full HMD symbology concurrently, such as the Eurofighter Typhoon’s helmet-mounted symbology system (HMSS) and some Scorpion HMCS variants. These helmet systems have been used by selected A-3 and ANG F-10 pilots and are planned for F-16 integration to exploit off-boresight launch capabilities with advanced missiles.
Multifunction Advanced Data Link (MADL) and Link-16
The Multifunction Advanced Data Link (MADL) is a secure datalink that allows F-35s to exchange information with each other and with other platforms that support the technology, such as the B-2 bomber and ships equipped with the AEGIS combat system. MADL enhances formation-level capability by sharing each aircraft’s sensor data to create a broader common operational picture. The F-35 also carries Link-16 for communication with legacy platforms lacking MADL, allowing the F-35 to act as a sensor and data amplifier for older assets.
Helmet Systems on Other Fighters
According to Eurofighter documentation, the Typhoon’s HMSS offers lower latency, higher clarity, improved symbology and night-vision compatibility compared with the most common legacy helmet systems, such as the U.S. JHMCS (Joint Helmet Mounted Cueing System), which entered service in the late 1990s and equips many U.S. F-16, F-18 and F-15 aircraft. HMSS and similar systems provide critical flight and weapons cueing symbology overlaid on the pilot’s line of sight, enhancing performance in air-to-air engagements.
In a recent Alaska Red Flag exercise, an American F-22 pilot who engaged in mixed-aircraft dogfights with German Typhoons was reportedly not equipped with a helmet display, underscoring differences in helmet integration across platforms.
JHMCS is a multi-role system that enhances situational awareness and enables head-controlled cueing of aircraft sensors and weapons. In air-to-air missions, JHMCS combined with the AIM-9X enables high off-boresight missile engagements by allowing the pilot to cue the weapon simply by looking at the target. In air-to-ground missions, JHMCS can be used with targeting sensors and precision-guided munitions for accurate strikes.
Scorpion Helmet Cueing System
The Scorpion helmet cueing system, developed by GenTexVisionix, is a single-lens, full-color HMD designed to be adaptable to various helmet shells. It requires a small interface control unit and a cockpit-mounted magnetic sensor. The system projects full-color, dynamic flight and mission data through a large-field, transparent waveguide directly into the crew’s line of sight, allowing the pilot to keep head-up and significantly improving real-time situational awareness.
Scorpion provides a 26° x 20° field of view and fully integrates with aircraft avionics without requiring extensive avionics bay integration. It can provide GPS coordinates for designated points for aiming or handover to other platforms. The system is installed via an interface control unit mounted in the cockpit and supports:
- System control over an Ethernet data bus (or via a control panel)
- A line-replaceable unit mountable in a side-console DZUS rail
- An inertial-optical hybrid tracker that requires no mapping
- System interfaces over Ethernet or MIL-STD-1553B
- Data transfer boxes up to 128 GB
Scorpion is an open system allowing pilots to customize their cockpit by selecting Scorpion features and prioritizing displayed data. Pilots no longer need to continuously scan cockpit instruments and displays; necessary data are available in a virtual HUD with a 3600 x 3600 conformal color symbology system overlaid on the real world. Symbology is programmed by the integrator and downloaded by the mission system at startup. Both video and symbols are scalable, and placement can be defined in any of four coordinate frames: Earth (latitude, longitude, altitude), aircraft (azimuth, elevation, roll), cockpit (X, Y, Z relative to the design eye) and helmet (azimuth, elevation, roll relative to the helmet sight).
The Scorpion display module is compact and does not impose a significant weight penalty on the pilot’s head; it can be flipped and swung out when not in use. The helmet supports full day-night transition missions; video demonstrated takeoff at dusk without NVGs, followed by flight phases using NVGs. The system continues to provide HUD-like symbols and video feeds during NVG connect/disconnect events.
Weapons Stations and Internal Gun
The F-35A carries an internal four-barrel 25 mm GAU-22/A cannon and two internal weapon bays. Each weapon bay can carry a mix of one air-to-air weapon and one air-to-ground weapon, up to a 2,000-pound warhead, or two air-to-air weapons. In a so-called "beast mode" where stealth is not required, the F-35 can use three external pylons per wing: the inboard station for loads up to 5,000 pounds, the mid-station for loads up to 2,000 pounds and the outboard station reserved for air-to-air missiles.
The last major avionics system to note is the GAU-22/A internal cannon. Hidden behind a closed door to preserve stealth, the GAU-22/A is based on the proven GAU-12/U 25 mm cannon used on the AV-8B Harrier II, LAV-AD amphibious vehicles and AC-130U gunships, but with one fewer barrel. It is lighter and mounted above the left intake on the F-35A. The weapon fires at approximately 3,300 rounds per minute. Given the A model’s internal capacity of 181 rounds, that corresponds to roughly 4 seconds of continuous fire, or more practically, multiple short bursts.
The GAU-22/A has been a subject of debate: critics note the limited ammunition load compared with the A-10’s GAU-8/A Avenger, which carries about 1,174 rounds of 30 mm, and concerns raised in a 2017 DOT&E report about long and right aiming bias. It is not clear whether all accuracy issues have been fully resolved.
Training footage showed the cannon being fired while the aircraft carried two external pylons with an inert AIM-9X Sidewinder on each pylon.
Although the F-35A carries the internal GAU-22/A, the B (STOVL) and C (carrier) variants use an external gun pod that holds 220 rounds.
