Italian F-35s intercept a Russian An-124 over the Baltic Sea. Technical focus on the use of EOTS and DAS for identification.
Two F-35As from the Aeronautica Militare, deployed to Ämari (Estonia) for NATO air policing, intercepted an Antonov An-124 “Ruslan” flying in international airspace near the Kaliningrad region. The QRA alert led to a takeoff in less than 15 minutes, followed by controlled visual identification. The pilots combined passive detection from the Distributed Aperture System (DAS) — 360° infrared imaging — with the high resolution of the Electro-Optical Targeting System (EOTS) to confirm the type of aircraft, its behavior, and its compliance with aviation rules. The AN/APG-81 AESA radar remained in support, with sensor fusion and data link ensuring real-time sharing with NATO’s CAOC. The An-124 is a strategic transport aircraft 69 m long with a wingspan of 73.3 m, cruising at around 800 km/h at an altitude of 10–11 km. The combined use of DAS + EOTS allows for remote identification, limiting risky approaches while remaining neutral and proportionate in Baltic airspace.
Operational context and NATO posture
The interception of a Russian An-124 by Italian F-35s is part of the Baltic Air Policing mission. Two aircraft based in Ämari were scrambled at the request of the Combined Air Operations Center (CAOC) after detecting Russian military traffic near NATO airspace. The flight took place outside the borders, in international airspace over the Baltic Sea. The crews applied the QRA rules of engagement: immediate takeoff, rapid climb to 10–12 km, stabilized interception, radio contact on 121.5 MHz, identification and tracking at a safe distance. The 24/7 QRA requires permanent availability; the objective is twofold: deterrence and air safety in Europe, without causing any incidents. In 2024, NATO reported more than 400 alert takeoffs in Europe; in the Baltic region, interceptions related to Russian flights without flight plans or with irregular transponders are frequent and documented by national authorities.
Profile of the An-124 “Ruslan” and identification clues
The Antonov An-124 is a heavy four-engine transport aircraft. Approximately 69 m long, with a wingspan of approximately 73.3 m and a height of approximately 21 m, it can carry up to 150 t of payload and has a maximum takeoff weight of 405 t. Its cruising speed is around 800 km/h with an operational ceiling of around 11–12 km. It has a distinctive silhouette: high wings, four Lotarev D-18 turbojet engines of ≈230–250 kN each, an articulated nose for front loading, a 24-wheel main landing gear, and a classic tail. For F-35 crews, these attributes provide points of identification from a distance: intense heat signature from the four engines, IR signature from the leading edge and areas of aerodynamic friction, length/wingspan ratio, and heat halo from the braking areas after descent. An-124 interceptions are less common than those of Su-27 fighters or Su-24 attack aircraft, which reinforces the value of electro-optical identification for documenting the type, trajectory, and conduct of the flight.
The F-35’s DAS system and 360° infrared detection
The DAS (AN/AAQ-37) equips each F-35 with six infrared sensors distributed across the airframe. It provides continuous spherical coverage (4π steradians) without manual pointing. In an air policing mission, pilots often favor a passive approach: the DAS detects and tracks the aircraft of interest using its infrared energy (exhaust, skin heating), then displays the imagery directly on the Helmet Mounted Display. The system’s sensitivity has been demonstrated in tests showing the detection and tracking of energetic objects at very long ranges (up to more than 1,200 km for rocket launches during demonstrations). In practical terms, on an An-124 in cruise mode, the DAS produces a passive track that can be used at long range, cues the AN/APG-81 radar if necessary, and feeds the sensor fusion to stabilize the interception without prolonged active emission. This 360° infrared surveillance also detects anomalies (asymmetric heating, unusual drag), which are useful for assessing a possible technical condition or non-compliant flight profile.
The EOTS system and positive remote identification
The EOTS (AN/AAQ-40), integrated under the nose of the F-35, combines high-resolution FLIR, IRST capability, automatic tracking, laser rangefinding, and designation. Its main infrared spectrum (3–5 µm mid-band) optimizes the reading of thermal contrasts. In a heavy transport interception, the typical tactic is as follows: the EOTS is slaved to a DAS or radar track; the pilot switches to a narrow field of view with digital zoom to refine the aircraft’s silhouette; he compares the apparent length, width-to-length ratio, engine position, nose shape, and landing gear configuration. At the regulatory short range, EOTS imaging can be used to identify markings or confirm a version (e.g., An-124-100). In adverse weather conditions, thermal imaging offers a clear advantage over simple TV optics. EOTS therefore acts as a remote identification sensor, complementing DAS. The Advanced EOTS currently being deployed further improves definition and extends spectral bands, but the basic sensor is already suitable for aerial electro-optical reconnaissance.
Sensor fusion and interception guidance
The F-35 capitalizes on advanced sensor fusion: DAS and EOTS (infrared), AN/APG-81 (AESA radar), AN/ASQ-239 (electronic warfare), and CNI (MADL/Link 16). In air policing, passive flow takes precedence to minimize emissions; radar takes over in long-range air-to-air mode to refine speed and altitude and ensure avoidance. Correlated data is shared with the CAOC and the patrol’s No. 2. The approach remains measured: vertical or lateral echelon, regulatory separation, communication on 121.5 MHz, then escort if required. With an An-124 cruising at ≈ 800 km/h at 10–11 km, an F-35A can stabilize the junction in a few minutes thanks to its speed (≈ Mach 1.6 at peak) and high climb rate, while maintaining sensor initiative. This method avoids sudden approaches, limits wear and tear, and preserves the air safety of third parties.
Practical uses of EOTS and DAS against an An-124
On a strategic transport aircraft, the infrared footprint is massive: four D-18 engines each deliver ≈230–250 kN; EOTS isolates hot spots (nozzles, leading edges, ventured areas) and reconstructs an accurate silhouette. At the same time, DAS keeps track of the aircraft’s maneuvers: climbing turns, level flight, or descent. In a narrow field, EOTS helps distinguish an An-124 from an Il-76 by the shape of the nose, the distribution of the landing gear, the geometry of the tailplane, and the distance between the nacelles. At medium range, thermal vibrations from flaps and trailing edges provide additional clues. If the aircraft is flying without a transponder or outside the ATC slot, the CAOC may request extended tracking, still outside sovereign airspace. The expected result: type identification, time-stamped thermal photos/videos, reporting to NATO authorities, and removal of doubt about the nature of the flight. This method favors objective evidence from sensors rather than assumptions and enhances the traceability of interactions.
Operational and strategic challenges
Air safety in Europe relies on a credible and predictable posture. In the Baltic, Italian F-35s demonstrate the ability to monitor military flights to and from Kaliningrad. Interceptions of large aircraft are rare but sensitive: they test radio discipline, cooperation with civil controls, and remote identification capabilities. The DAS + EOTS duo reduces the need for close approaches and lowers the risk for crews. On a macro level, NATO observed a 20-25% increase in scrambles in the Baltic in the first quarter of 2024, reflecting increased activities and exercises. Baltic Air Policing rotations are celebrating their 20th anniversary; the arrival of 5th generation aircraft standardizes procedures where passive detection, fusion, and sharing prevail over the race for force. For the Aeronautica Militare, this is valuable experience: NATO integration, mastery of QRA in the Baltic climate, and validation of measured interception against strategic platforms.
The technical and operational scope for European forces
Beyond the event itself, the rigorous use of EOTS and DAS imposes certain requirements: line-level sensor maintenance, regular calibrations, training in IR interpretation, and EMCON (emissions management) discipline. The unit cost of a modern air-to-air missile runs into hundreds of thousands of euros; each interception avoided thanks to long-range identification saves resources and reduces attrition. In terms of coordination, Link 16 connects aircraft, ships, and radars; MADL connects F-35s to each other without compromising discretion. The objective is clear: detect early, classify accurately, identify cleanly, then document and share. This factual and sober approach is well suited to the densely populated skies of Northern Europe. It also responds to a reality: interception is not a duel, but a safety procedure, where the sensor preserves as much as it monitors. As such, EOTS and DAS constitute a concrete European advantage when operated methodically and without overconfidence.
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